Prolactin and Low Testosterone: Why the Connection Matters
Testosterone is the primary male sex hormone, crucial for sexual development, muscle mass, bone density, mood, and overall vitality. Prolactin, on the other hand, is a hormone best known for stimulating breast milk production in women. At first glance, these two hormones seem unrelated. However, prolactin and testosterone have an important inverse relationship in men’s health. High levels of prolactin can actually cause low testosterone, leading to symptoms like low sex drive and fatigue[1][2]. Conversely, changes in testosterone levels (for example, through testosterone therapy) can influence prolactin production. This interplay is why healthcare providers often evaluate both hormones together when assessing hormonal health in men.
Why is prolactin important in men? The pituitary gland – a pea-sized organ at the base of the brain (highlighted in the image below) – produces prolactin along with other critical hormones. In men, prolactin isn’t for milk production; instead, excess prolactin can disrupt the reproductive hormone axis. Prolactin acts as a brake on the hypothalamic-pituitary-gonadal (HPG) axis: high prolactin inhibits the secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus, which in turn lowers luteinizing hormone (LH) from the pituitary[1]. LH is the hormone that tells the testes to produce testosterone. Thus, an excess of prolactin effectively puts the brakes on testosterone production[3][1]. Men with elevated prolactin (a condition called hyperprolactinemia) often develop hypogonadism (testosterone deficiency) with symptoms such as decreased libido, erectile dysfunction, infertility, fatigue, and even bone density loss[1][2]. High prolactin can also cause galactorrhea (milk discharge from the breast) and, in some cases, breast enlargement (gynecomastia) in men[4][2] – although these symptoms are less common in men than in women.
Because prolactin has such a suppressive effect on male hormone balance, it is standard medical practice to measure prolactin levels whenever a man is found to have low testosterone (especially with low or normal gonadotropins). In other words, if lab tests confirm a low testosterone level, doctors will typically check serum prolactin as part of the work-up[5]. This helps determine if a treatable cause like a prolactin-secreting pituitary tumor could be responsible for the testosterone deficiency. Guidelines from urology and endocrinology organizations emphasize this step: low testosterone + inappropriately low/normal LH = check prolactin[5][3]. The reason is that hyperprolactinemia is a well-known reversible cause of male hypogonadism. Although prolactinomas (pituitary tumors that secrete prolactin) are a relatively uncommon cause of low testosterone, it’s critical not to miss them because they are treatable and can have other serious effects (tumor growth causing headaches or vision problems)[6][7]. In one review, researchers noted that hyperprolactinemia from a pituitary adenoma is a rare cause of erectile dysfunction, but whenever a man has erectile dysfunction plus low testosterone, a prolactin level should be measured to rule this out[6]. In clinical practice, a significant proportion of men with prolactinomas present with sexual symptoms: men with prolactin-secreting tumors often report low libido, impotence, and sometimes infertility due to the associated testosterone deficiency[2][8].
Key point: A high prolactin level in a man can explain why his testosterone is low. As we know, “a high prolactin causes LH to be suppressed which leads to low testosterone”[3]. Therefore, checking prolactin is essential in the evaluation of male hypogonadism (particularly secondary hypogonadism, where the problem lies in the pituitary or hypothalamus). If prolactin comes back elevated, it often changes the management plan: the focus may shift to treating the high prolactin (and its cause) rather than jumping straight to testosterone replacement.
Causes of High Prolactin in Men and Health Implications
When a man is found to have high prolactin, the next step is figuring out why. There are several potential causes of hyperprolactinemia in men:
- Pituitary Tumors (Prolactinomas): The most common pathological cause is a benign tumor of the pituitary gland that secretes prolactin. Prolactinomas can be tiny (microadenomas <10 mm) or large (macroadenomas ≥10 mm). Men tend to have larger tumors by the time of diagnosis (often macroadenomas) than women[9]. These tumors can drive prolactin levels very high (often hundreds or thousands of ng/mL) and cause symptoms of low testosterone and sometimes headaches or vision changes if the tumor presses on nearby structures[7][10].
- Medications: A variety of drugs can raise prolactin as a side effect. Notably, certain antipsychotics (e.g. risperidone, haloperidol), some antidepressants, anti-nausea medications (metoclopramide, domperidone), high-dose estrogen (including some prostate cancer treatments or exposure to phytoestrogens), and opioid pain medications can increase prolactin by interfering with dopamine or stimulating prolactin release[11][12]. Typically, medication-induced prolactin elevations are more modest (often 25–100 ng/mL, rarely above ~200)[13]. If a man with low T is on one of these medications, the drug could be the culprit.
- Hypothyroidism: An underactive thyroid gland (high TSH) can cause elevated prolactin. This is because thyrotropin-releasing hormone (TRH), which is elevated in primary hypothyroidism, can stimulate prolactin release[14][15]. Thus, part of the evaluation of high prolactin is checking thyroid function; treating hypothyroidism can often normalize mildly elevated prolactin.
- Other Causes: Chronic kidney disease and liver disease can lead to reduced clearance of prolactin, causing higher levels[14]. Chest wall injuries or even frequent chest wall stimulation can raise prolactin (the body interprets it as nipple stimulation, which in breastfeeding would raise prolactin)[16]. And of course, stress alone can transiently raise prolactin (even a stressful blood draw can make prolactin spike slightly)[17][18]. For this reason, if a prolactin level comes back only mildly elevated, doctors will often recheck it on a different day after the patient is well-rested and fasting, to ensure it wasn’t just a stress response.
From a health perspective, untreated hyperprolactinemia in men can have several consequences. In addition to causing hypogonadism and sexual dysfunction, chronically low testosterone from high prolactin can contribute to infertility, depression, fatigue, and bone loss (osteoporosis)[1]. Men with long-standing low testosterone may develop decreases in muscle mass and increases in body fat. High prolactin itself can sometimes cause fatigue, mood changes, and even mild breast tissue growth. If a prolactinoma tumor is large, it can cause headaches or vision changes (classically loss of peripheral vision) due to pressure on the optic chiasm. These potential effects make it important to both identify and treat significant hyperprolactinemia.
The good news is that in many cases, treating the high prolactin can reverse these problems. We’ll discuss treatment shortly – including medications like bromocriptine and cabergoline that can lower prolactin levels and often restore normal testosterone production.
Testosterone Therapy and Prolactin: Understanding the Paradox
It’s intuitive that high prolactin can cause low testosterone, but the relationship can also work in the other direction: changing a man’s testosterone levels (for example, by giving testosterone therapy) can influence prolactin. Some men and clinicians have observed that when starting testosterone replacement therapy (TRT), prolactin levels might rise. Why would that happen?
Hormonal feedback loops: The endocrine system is full of feedback mechanisms. In the case of prolactin, its main regulators are dopamine (which inhibits prolactin secretion) and estrogen (which stimulates prolactin secretion)[19][20]. Normally, in males, testosterone is converted into a small amount of estrogen (estradiol) by the enzyme aromatase. This estradiol is actually important for male health (needed for bone maintenance, libido, etc.), but if estradiol levels become elevated, they can promote prolactin release. Exogenous testosterone (i.e., testosterone medication) can raise estradiol levels because some of the injected or applied testosterone will aromatize into estradiol. The higher the dose of testosterone, or the more body fat a man has (fat contains aromatase), the more estradiol may be produced from that testosterone. In essence, giving a man extra testosterone can indirectly increase the hormone (estrogen) that tells the pituitary to make more prolactin[21]. This is the primary mechanism behind reports of rising prolactin in some men on TRT: testosterone itself usually isn’t the direct stimulator – its conversion to estradiol is[21].
Interestingly, androgens and estrogens have opposite direct effects on prolactin regulation. Classic research has shown that androgens tend to suppress prolactin secretion, whereas estrogens increase prolactin secretion[22][23]. For example, a study in healthy men found that when they were given dihydrotestosterone (DHT, a non-aromatizable androgen), their prolactin levels decreased, and when normal men were given an androgen-blocker (spironolactone), their prolactin levels increased[24]. In the same study, giving an aromatase inhibitor (which lowered estradiol production) led to a drop in prolactin, supporting the idea that each man’s own endogenous estrogen levels drive prolactin[25][23]. So under usual circumstances, testosterone has a mild prolactin-lowering influence (via androgenic effect), while estradiol has a pro-prolactin influence. This dynamic creates a bit of a paradox when we introduce external testosterone: we raise androgens (which would lower prolactin) but also raise estrogens (which raise prolactin). The net effect can vary by individual. In most men, standard TRT doesn’t cause prolactin to skyrocket – prolactin usually remains in the normal range. However, some men do experience a rise in prolactin on testosterone therapy, especially if high doses are used or if they aromatize a lot of estrogen.
Clinical experience and case studies bear this out. For instance, it is not uncommon to find in men with hypogonadism and a known prolactin-secreting pituitary adenoma: that when they are started on testosterone replacement, their prolactin levels would rise significantly and even the tumor enlarged, and when testosterone was stopped, the prolactin level would fall again[26][27]. In these patients, the testosterone essentially “fed” the prolactinoma via conversion to estradiol, which stimulated the prolactin-secreting cells. Such dramatic cases are uncommon, but they highlight the potential interaction. An older study in the 1980s observed that giving a 100 mg depot testosterone injection to a group of older men caused a significant increase in prolactin by day 4 after the injection[28]. Notably, that study also found that men who had low baseline testosterone tended to have higher baseline prolactin (possibly because their lack of androgens left prolactin unopposed)[29]. These findings suggest that rapid changes in hormone levels – like the spike from a large testosterone dose – can temporarily disturb the prolactin balance.
It’s important to stress that most men on testosterone therapy will not develop clinically significant hyperprolactinemia. In general, TRT is considered to have a neutral or only minimal effect on prolactin in the average patient. Routine monitoring of prolactin during testosterone therapy isn’t usually recommended unless symptoms arise[30]. In fact, standard TRT monitoring protocols typically focus on testosterone levels, prostate-specific antigen (PSA), blood counts, and liver function, rather than prolactin[30]. However, being aware of the potential for prolactin changes is useful. If a man on testosterone begins to develop symptoms suggestive of high prolactin – for example, new breast tenderness/swelling, lactation (galactorrhea), persistent sexual dysfunction, or headaches or an elevation in estradiol. Then checking a prolactin level is warranted[31][32].
Why would testosterone therapy cause prolactin to increase? In summary: the aromatization to estradiol is the key mechanism[21]. Estradiol acts on the lactotroph cells of the pituitary to promote prolactin secretion. Additionally, big swings in hormone levels might play a role. Injectable testosterone, especially in longer-interval doses, causes peaks and troughs in hormone levels. A high peak (a few days after an injection) could overstimulate pituitary cells transiently. Some clinicians have theorized that using transdermal testosterone (daily gels or creams), which produce more stable testosterone levels, might reduce this risk compared to injections that spike higher[33]. Indeed, if a patient on injections is found to have rising prolactin and associated symptoms, one management strategy is to switch to a daily transdermal formulation to avoid the peaks[33].
Another factor to consider is that improved sexual function from TRT could lead to more frequent orgasm and ejaculation, and interestingly, orgasm itself causes a temporary increase in prolactin as part of the neuroendocrine refractory period. This post-orgasm prolactin surge is normal and short-lived, but theoretically, if someone’s sexual activity greatly increased on TRT, their average prolactin might run a tad higher (this is more speculative and typically wouldn’t cause out-of-range levels unless there’s another issue).
Take-home message: When we supplement testosterone, prolactin can sometimes increase as an indirect effect of higher estradiol levels. This isn’t a common side effect in most TRT patients, but it does occur. One medical review phrased it as: “Exogenous testosterone can paradoxically increase prolactin levels through aromatization to estradiol, though this is not a typical or common effect.”[34]. So physicians should be aware of it, particularly in men who have known pituitary disorders or who develop suggestive symptoms on therapy.
What if a man already has a prolactin-secreting pituitary adenoma (prolactinoma) and also has low testosterone? Doctors face a careful balance in such cases. The primary treatment would be to lower prolactin (with medication, as we’ll discuss next) to shrink the tumor and potentially let testosterone recover naturally. Testosterone replacement might still be given if needed for symptomatic relief, but it can complicate management. Some research indicates that introducing testosterone therapy in a man with a prolactinoma can reduce the effectiveness of prolactin-lowering medications – likely because the extra estradiol stimulation from testosterone makes the tumor less responsive to dopamine agonist drugs[35]. In dopamine-resistant prolactinomas, adding an aromatase inhibitor (to block testosterone’s conversion to estradiol) has shown benefit in bringing prolactin levels under control[36][35]. In other words, if testosterone is deemed necessary in a man with a prolactinoma, combining it with an aromatase inhibitor or using a non-aromatizable androgen (like DHT) could prevent fueling the prolactin issue[37][38]. This is a specialized scenario, but it highlights how closely linked these hormones are and the importance of individualized therapy.
Treating Elevated Prolactin: Bromocriptine and Cabergoline
When prolactin levels are high and causing problems, treating the underlying hyperprolactinemia is a priority. The first-line treatment for most cases of significant hyperprolactinemia (especially from a prolactinoma) is medication with a dopamine agonist. Dopamine is the body’s natural inhibitor of prolactin, so dopamine agonist drugs mimic the action of dopamine on the pituitary’s lactotroph cells, thereby shutting down prolactin release[19][39]. The two main dopamine agonists used are bromocriptine and cabergoline (they are available as Parlodel® and Dostinex® respectively, including in generic forms). A third agent, quinagolide, is used in some countries outside the US (e.g. Europe and Canada) but not available in the United States[40][41].
Cabergoline vs. Bromocriptine: Cabergoline is a newer agent and has largely superseded bromocriptine as the preferred therapy due to its greater efficacy and better tolerability. Cabergoline is long-acting, so it’s typically taken just once or twice per week (e.g. 0.25 mg twice weekly to start). Bromocriptine usually must be taken daily (often 2–3 times per day) to adequately control prolactin, and it tends to cause more side effects (notably nausea, lightheadedness, and dizziness due to blood pressure lowering)[42]. Both drugs are quite effective at reducing prolactin levels, but studies show cabergoline can normalize prolactin in a higher percentage of patients and is better at shrinking pituitary tumors[43][44]. For example, clinical guidelines note that over 90% of patients with a prolactinoma will have their prolactin levels drop into the normal range with dopamine agonist therapy, and significant tumor size reduction occurs in the majority as well[45]. Cabergoline can achieve normal prolactin in about 70–85% of patients, including many with larger tumors, whereas bromocriptine’s success rate is somewhat lower (around 70% in some series)[46][47]. In practice, if cabergoline is available and not contraindicated, it is usually the first choice. Bromocriptine is still used in some cases: for instance, if a patient cannot tolerate cabergoline or if a woman with a microprolactinoma is trying to conceive (bromocriptine has a longer track record in pregnancy). But for most men, cabergoline’s ease of use and potency make it preferable. As a Pituitary Society resource succinctly states: “While both bromocriptine and cabergoline are effective, cabergoline works better to lower prolactin levels and reduce tumor size with fewer side effects.”[42]
How these medications help: By lowering prolactin levels, dopamine agonists remove the hormonal suppression on the gonadal axis. In many cases, this allows the body to resume normal testosterone production. Men with hyperprolactinemia often see their testosterone climb back up as prolactin falls. In fact, the primary goals of treating a prolactinoma are to normalize prolactin and restore gonadal function, as well as to reduce tumor size and relieve any mass effects[48]. Studies have documented improvements in testosterone levels and symptoms after prolactin-lowering therapy. For example, one study found that after six months of cabergoline treatment, men with high prolactin had normalization of testosterone levels and improved erectile function in most cases[49]. Another review noted that cabergoline therapy for 16 weeks significantly improved libido and sexual function in hyperprolactinemic patients, whereas bromocriptine did not show as much improvement in sexual side effects in that short timeframe[50][51]. These medications not only help regain sexual health but can also improve fertility if it was impaired by prolactin (since sperm production should resume when testosterone and gonadotropins normalize).
It’s worth noting that recovery of full gonadal function isn’t guaranteed in every single case – if a prolactin-secreting tumor was very large and long-standing, sometimes the pituitary’s gonadotroph cells (which produce LH and FSH) can be permanently damaged. In many men, however, the hypogonadism is functional and reversible with prolactin reduction. One study reported that about 80% of men with prolactinomas achieved a return to normal testosterone levels (eugonadism) after several years of dopamine agonist treatment and tumor control[52][53]. In cases where testosterone remains low despite normal prolactin (perhaps due to irreversible pituitary damage), testosterone replacement can be added – but only after prolactin is controlled and under careful monitoring (as discussed, adding TRT in prolactinoma patients requires caution).
Dosing and duration: A typical starting dose for cabergoline is 0.25 mg twice a week. It can be gradually increased (e.g. 0.5 mg twice weekly, etc.) until prolactin levels normalize or the maximum tolerated dose is reached. Most patients respond to relatively low doses, but a few may require higher doses (there are case reports of very high-dose cabergoline in resistant cases). Bromocriptine might be started at 1.25 mg (half a 2.5 mg tablet) at night to minimize side effects, then built up to 2.5 mg twice daily or more as needed. These medications are usually continued for a long duration. If the prolactin source is a microadenoma, after 1–2 years of normal prolactin and tumor shrinkage, a trial off medication may be considered to see if the tumor has resolved. For macroadenomas, treatment is often ongoing for many years, and occasionally indefinitely, to keep the tumor in check. Prolactin levels guide the dosing – doctors aim to keep prolactin in the normal range, and periodic MRI scans are done to monitor tumor size (e.g. at 6 months, 1 year, then yearly or every couple of years).
Effects on symptoms: Lowering prolactin often leads to noticeable symptom relief within weeks to months. Libido and energy can improve as testosterone rises. Erectile dysfunction related to hyperprolactinemia can resolve. Many men also report improved mood and well-being. If there was breast enlargement or lactation, these usually subside. Any visual symptoms from a large tumor may improve as the tumor shrinks off the optic nerves. It’s truly rewarding that a vast majority of patients can be treated effectively with just these pills, avoiding the need for pituitary surgery in most cases. Surgery (transsphenoidal pituitary surgery) is generally reserved for those who cannot tolerate the medications or whose tumors do not respond (e.g. very rare medication-resistant cases, or if the tumor is causing acute vision threat and needs debulking). Radiation is an even more distant second-line for aggressive cases. But for over 90% of prolactinoma patients, dopamine agonists do the job[45].
Safety and side effects: Bromocriptine and cabergoline are generally safe but not free of side effects. The most common side effect is nausea – many patients initially feel queasy or even vomit, because these drugs stimulate dopamine receptors in the brain’s vomiting center. This is why we start at a low dose and often advise taking the pill with food or at night. Cabergoline’s weekly dosing tends to cause less nausea than bromocriptine’s daily dosing in practice[44]. Other side effects can include headaches, fatigue, dizziness (especially orthostatic hypotension – feeling lightheaded upon standing due to lowered blood pressure), nasal stuffiness, and, in high doses, mood changes. At the doses used for prolactinomas, serious side effects are rare. High-dose cabergoline (much higher than used in prolactinoma, such as in Parkinson’s disease patients) has been linked to heart valve issues; fortunately, the low doses for endocrine use have not shown a significant increase in valvular heart disease in most studies[54]. Nonetheless, if someone is on cabergoline long-term, a periodic cardiac ultrasound might be considered by some doctors as a precaution. Another unusual side effect of dopamine agonists, especially noted in Parkinson’s patients on higher doses, is impulse control disorders (e.g. pathological gambling, hypersexuality)[55]. This is thought to be due to stimulation of certain dopamine pathways in the brain’s reward center. It’s quite uncommon at the doses for prolactinomas, but patients should be made aware to report any odd changes in behavior or impulse control. Generally, cabergoline is very well-tolerated for most men; bromocriptine can be a bit tougher due to the GI side effects, but many tolerate it if they titrate slowly.
Impact on testosterone levels: As mentioned, successfully treating hyperprolactinemia often allows a man’s own testosterone production to rebound. For example, a 2003 clinical trial demonstrated that men with prolactin-induced hypogonadism who took cabergoline for 6 months had their total testosterone levels rise from hypogonadal range back to normal, along with improvement in sexual function[49]. Another report found that even after just 8 weeks on cabergoline, men noted increases in libido and potency corresponding with hormonal normalization[50][56]. Thus, dopamine agonists not only solve the lab value (high prolactin) but also address the downstream consequences (low testosterone and sexual symptoms). In a sense, they can “cure” a case of low testosterone that was secondary to high prolactin. Of course, if a man’s testes were not producing testosterone for a long period, it might take a few months for full function to come back, and as noted earlier, some men may still need supplemental testosterone if the gonadotropin cells were permanently injured. But the first approach in a low-T patient with high prolactin is to fix the prolactin.
What about situations where testosterone therapy itself might have caused an elevation in prolactin? In such cases, one might consider using a dopamine agonist to bring prolactin down. Indeed, bromocriptine or cabergoline can be used to treat any symptomatic hyperprolactinemia, regardless of cause. If a man on TRT has an out-of-range prolactin and is experiencing issues like breast symptoms or sexual dysfunction, a dopamine agonist could be prescribed. However, an interesting observation from some case reports is that dopamine agonists may not always fully counteract testosterone-induced prolactin elevation if the mechanism is via increased estradiol. One case of testosterone-induced macroprolactinoma growth found that even increasing cabergoline doses didn’t completely suppress prolactin until an aromatase inhibitor was added[35][57]. The takeaway is that if high prolactin occurs on testosterone therapy, addressing the root cause (excess aromatization) is important – that might mean lowering the testosterone dose, switching the delivery method, or adding a low-dose aromatase inhibitor, rather than relying solely on a dopamine agonist. For most typical TRT patients, though, this scenario is unlikely.
In summary, bromocriptine and cabergoline are effective tools to treat high prolactin. They often eliminate the need for testosterone therapy by naturally boosting the body’s testosterone (by removing prolactin’s inhibition). They also treat the source of the problem (like shrinking a prolactinoma). These medications have transformed what used to sometimes require neurosurgery into a medical treatment. Both patients and providers should understand that if a man’s low testosterone is found to be due to high prolactin, the priority is to treat the prolactin issue first. Testosterone supplementation may be a secondary consideration and, if needed, is usually introduced after prolactin levels are controlled (or in parallel with careful observation).
Other Hormonal Considerations When Supplementing Testosterone
Managing low testosterone isn’t just about raising testosterone levels. Because of the complex feedback loops in the endocrine system, introducing testosterone therapy can affect several other hormones and health parameters. Both healthcare providers and patients should be aware of these effects so they can be monitored and managed. Here are some key considerations:
1. Estradiol (Estrogen): As discussed earlier, some of the testosterone in a man’s body is naturally converted to estradiol, a form of estrogen. On TRT, especially at higher doses or with injectable forms, estradiol levels often increase. Estradiol is not an “enemy” – men need some estrogen for bone health, brain function, and even sexual function (estrogen contributes to libido and erectile function too). However, if estradiol rises too high, men can experience side effects such as fluid retention, increased blood pressure, gynecomastia (swelling/tenderness of breast tissue), or emotional lability. There’s individual variability: some men are very sensitive to estrogen levels and may get symptoms at moderately elevated levels, while others feel fine. Many specialists do measure estradiol levels in men receiving testosterone to ensure they’re not excessively high[58][59]. For instance, a men’s health clinic might check a baseline estradiol before starting TRT and then periodically during treatment[58]. If a man on TRT develops high estradiol with symptoms, doctors can prescribe an aromatase inhibitor (AI) such as anastrozole to bring estradiol down a bit[58]. The goal is to keep estradiol in an optimal range – not too high, but also not too low (since too little estrogen can cause joint pain, poor libido, and bone loss). It’s a delicate balance. Current guidelines do not recommend routine use of AIs for every man on TRT; they are used selectively if needed. Lifestyle factors can also help – losing excess body fat (which harbors aromatase enzyme) can naturally reduce estradiol production. In summary, monitoring estradiol is often part of managing testosterone therapy, and addressing it is important for comfort and safety. If you notice symptoms like nipple soreness or swelling while on TRT, bring it up to your provider – an estradiol check may be done and appropriate therapy started.
2. Gonadotropins (LH and FSH) and Fertility: One predictable effect of taking testosterone is that it will suppress your pituitary gland’s production of LH and FSH (through negative feedback on the hypothalamus and pituitary)[60]. This means that while you’re on TRT, your testes get the signal to essentially go “offline” – they won’t produce much, if any, testosterone on their own, and importantly, they also won’t produce sperm. In fact, exogenous testosterone has been studied as a form of male birth control, because high testosterone in the bloodstream suppresses LH/FSH so much that sperm production falls dramatically, often to zero[60][61]. For a hypogonadal man who is done having children or doesn’t desire fertility, this isn’t a big issue day-to-day (aside from testicular shrinkage that can occur from disuse). But for a man who may want to father children, TRT can cause temporary infertility. It’s crucial that patients and providers discuss this upfront. The infertility caused by TRT is usually reversible after stopping therapy, but the recovery can take months (typically 3-6 months to recover sperm counts, sometimes up to a year)[62][63]. In some cases, a man might not fully recover his baseline sperm count, though the majority do return to the fertile range[62][63]. If maintaining fertility is a priority, there are alternative treatments for low testosterone. For example, clomiphene citrate (Clomid) or enclomiphene can be used; these drugs stimulate the body’s own LH/FSH production and thereby increase testosterone and preserve (or even boost) sperm production[64][65]. Another option is using hCG (human chorionic gonadotropin) injections, which act like LH to stimulate the testes – sometimes hCG is used alone or alongside low-dose testosterone to maintain fertility. The bottom line is: exogenous testosterone should be avoided or used with caution in men who wish to remain fertile[66]. If TRT is absolutely necessary in a young man, adding hCG can be considered to support sperm production, but it’s best to consult a fertility specialist or endocrinologist in such cases. For older men or those for whom fertility is not a concern, this issue is less relevant, but they should still know that their LH and FSH will be near zero on TRT – that is expected and not in itself harmful, but simply a reflection of the hormone replacement.
3. Thyroid Function: Thyroid hormones and testosterone intersect in subtle ways. Severe hypothyroidism can cause a drop in total testosterone (by increasing prolactin and decreasing sex hormone binding globulin), while hyperthyroidism can increase SHBG and alter testosterone levels as well. In evaluating a man for low testosterone, doctors often check thyroid function tests, because fatigue, low mood, and sexual dysfunction can also stem from thyroid imbalances. Additionally, as noted, untreated hypothyroidism can elevate prolactin, compounding a hypogonadism scenario[14][15]. Treating a thyroid disorder may, in turn, improve testosterone levels slightly or at least improve symptoms. When supplementing testosterone, there isn’t usually a need to modify thyroid hormone doses in those with thyroid disease, but it’s just good practice to ensure thyroid levels are optimized as part of overall endocrine health. In short, thyroid hormone is another piece of the puzzle – comprehensive care means not overlooking a thyroid problem that could be contributing to the patient’s symptoms or even to the prolactin elevation.
4. Adrenal and Pituitary Hormones: If a secondary hypogonadism (low LH/FSH) is identified, sometimes clinicians will do a broader pituitary evaluation. This might include checking morning cortisol levels (to screen for adrenal insufficiency), growth hormone status (IGF-1 level), and so on, especially if a pituitary tumor is known or suspected. For example, large prolactinomas can sometimes co-secrete other hormones or cause partial pituitary failure affecting thyroid or adrenal function[67]. Prior to starting testosterone in a man with possible pituitary disease, it’s important to ensure he isn’t cortisol-deficient – because giving testosterone (an anabolic hormone) in an untreated cortisol-deficient state could worsen adrenal insufficiency. Thus, in relevant cases (e.g. a man has very low LH, high prolactin, and symptoms of adrenal insufficiency), an endocrinologist might test adrenal function and other pituitary hormones. This is part of the “full picture” approach. For the average hypogonadal man without red flags for other issues, extensive pituitary testing isn’t necessary, but it’s something to keep in mind if symptoms don’t fully resolve or if other signs point to multi-hormonal problems.
5. DHT (Dihydrotestosterone) and Androgenic Effects: Testosterone in the body is also converted to dihydrotestosterone (DHT) by the 5-alpha reductase enzyme (especially in the skin, prostate, and liver). DHT is a more potent androgen than testosterone itself. It’s responsible for certain androgenic effects like facial/body hair, acne, prostate enlargement, and male-pattern baldness. Different forms of TRT affect DHT levels differently: transdermal gels tend to raise DHT more than injections, because skin has lots of 5-alpha reductase. Oral testosterone derivatives (like old formulations of testosterone undecanoate) can also produce more DHT. Why does this matter? Elevated DHT can contribute to side effects such as acne breakouts or acceleration of hair loss in those genetically predisposed. It also acts on the prostate gland – though current evidence does not show that TRT increases prostate cancer risk, it can increase prostate volume somewhat and worsen symptoms of benign prostatic hyperplasia (BPH) in some men (like urinary difficulty). We usually don’t measure DHT levels routinely during therapy, but being aware of DHT-related effects is important. If a man on TRT develops significant acne or alopecia (hair thinning), sometimes doctors add a 5-alpha reductase inhibitor (like finasteride) to mitigate those symptoms by reducing DHT. This is done cautiously, as finasteride itself can have sexual side effects in some men. An alternative strategy is lowering the testosterone dose if possible. Overall, DHT is part of the testosterone ecosystem, and its effects are mostly “side effects” we monitor (skin and prostate changes).
6. Prostate Health (PSA levels): Before starting TRT, guidelines recommend checking a PSA (prostate-specific antigen) blood test and performing a prostate exam, especially in men over 40-45 or those at risk for prostate cancer[68]. This is to screen for any occult prostate cancer, since adding testosterone could theoretically stimulate an existing cancer. Men with active prostate cancer are generally contraindicated from TRT until treated. During testosterone therapy, PSA is typically monitored periodically (e.g. every 6-12 months) to watch for any concerning rises. Testosterone can convert to DHT which can make the prostate gland more metabolically active – potentially increasing PSA slightly and enlarging the gland. Most studies have not shown TRT to significantly increase prostate cancer incidence, but vigilance is maintained. If a man’s PSA rises rapidly or above the normal range while on TRT, the therapy might be paused and a urological evaluation (possibly a biopsy) done to exclude cancer[68]. Also, if severe urinary symptoms develop (difficulty urinating, etc.), the dose might need reduction or a BPH medication added. The key point is that prostate health must be tracked during TRT. This is why in the U.S., testosterone prescriptions often come with the plan for regular PSA tests. It’s a safety net.
7. Red Blood Cell Count (Hematocrit): Testosterone has a known effect of stimulating erythropoiesis (red blood cell production). Many men on TRT will experience an increase in their hemoglobin and hematocrit (the proportion of blood volume occupied by red cells). Sometimes this is beneficial – for example, if a man had anemia of testosterone deficiency, TRT can correct it. But it can overshoot. Polycythemia (excess red blood cells) can occur on TRT, especially with injectables at higher doses. A hematocrit above ~52-54% is concerning because it may thicken the blood and increase the risk of clotting problems (like stroke or thromboembolism). It’s one of the most common reasons a doctor might have to lower the testosterone dose or temporarily halt therapy. Guidelines advise checking blood count (hematocrit) at baseline and then during therapy (e.g. at 3-6 months, then annually)[30][69]. If hematocrit goes above 54%, the recommendation is to take action: either reduce the dose of testosterone, hold therapy until it comes down, or have the patient donate a unit of blood (therapeutic phlebotomy) to bring it down[70][33]. Patients should also stay well hydrated. Symptoms of very high hematocrit can include ruddy complexion, headaches, or blurred vision, but often it’s silent – hence lab monitoring is crucial. As an example of monitoring: one clinic notes they always get a baseline hematocrit before TRT and then watch for any “supraphysiologic” rise, intervening by phlebotomy or dose adjustment if needed[69]. Keeping the hematocrit in a safe range ensures we reap testosterone’s benefits without undue risk.
8. Liver and Metabolic Parameters: Unlike the old oral anabolic steroids (which could harm the liver), modern testosterone therapies (injections, transdermals) are not particularly liver-toxic. Routine liver function tests are not mandatory but are often included in periodic bloodwork just to be thorough. Testosterone can have favorable effects on metabolism – for instance, improving muscle-to-fat ratio, insulin sensitivity, and cholesterol profile in men with deficiency[71][72]. However, in some cases, changes in estradiol and hematocrit might modestly impact blood pressure or lipids. It’s wise to keep an eye on the whole metabolic picture – many doctors will check lipid panels and blood glucose or A1c periodically in men on long-term TRT to ensure overall health is on track. Weight management and exercise synergize with TRT to improve these parameters.
In summary, testosterone therapy touches many aspects of physiology. A comprehensive treatment and monitoring plan addresses not just testosterone level itself but also related hormones and health markers. For patients: it’s important to follow through with scheduled lab tests and report any new symptoms (be it breast tenderness, changes in mood, urinary symptoms, etc.) to your provider. For providers: the art of TRT is in optimizing the benefits (improved energy, strength, libido, mood) while minimizing side effects – which means paying attention to estradiol, prolactin, hematocrit, PSA, and so on. The relationship between testosterone and prolactin exemplifies this interconnectedness: each hormone influences others. By understanding this relationship, we can tailor treatments to each individual’s needs.
Conclusion
Testosterone and prolactin have a dynamic, inverse relationship that is crucial in men’s health. High prolactin levels can suppress the production of testosterone, leading to significant symptoms and health consequences. This is why evaluating a man with low testosterone isn’t complete without checking prolactin – it could reveal an underlying, treatable cause like a prolactinoma or medication effect. On the flip side, altering a man’s testosterone levels (for example, via testosterone replacement therapy) can impact prolactin, sometimes causing it to rise due to increased estradiol. Both patients and healthcare providers should be aware of these interactions to avoid surprises during treatment.
The approach to low testosterone should always be comprehensive: find the cause, rather than just treating the number. If prolactin is the culprit, therapy directed at lowering prolactin (with medications like cabergoline or bromocriptine) can not only normalize hormone levels but often restore sexual function and fertility. These medications are effective in the vast majority of cases, essentially offering a medical cure for many prolactin-related hormone problems. When testosterone replacement is used, it should be done judiciously – with attention to other hormones and risk factors. Balancing testosterone, estradiol, and prolactin is a part of that puzzle, as is monitoring things like PSA and hematocrit for safety.
For patients, it’s empowering to understand why certain tests are ordered and how different hormones connect. If you’re a man undergoing evaluation for fatigue, erectile dysfunction, or other low-T symptoms, don’t be surprised when your doctor orders a prolactin level (among other labs). It’s not that they suspect you’re pregnant! – it’s that this lactation hormone can play a sneaky role in male hormonal health. And if you’re starting testosterone therapy, know that it’s not a set-and-forget treatment; it requires partnership with your provider to monitor your body’s response and adjust as needed.
For healthcare providers, a balanced tone with patients is key: we want to neither over-alarm (most cases of low T are not serious tumors) nor overlook important secondary causes. Educating patients that “we need to check your prolactin because sometimes a small benign growth in the pituitary could be affecting your testosterone” strikes the right balance. And if prolactin comes back high, providers should proceed with appropriate confirmatory tests (repeat measurement, check for macroprolactin, thyroid function, medication review, and likely pituitary MRI)[73][17]. Then treat based on findings.
In essence, hormones never act in isolation. Testosterone and prolactin are a prime example of this interconnectedness in the endocrine orchestra. By listening to all the players – checking the relevant labs and understanding their interplay – we can orchestrate the right treatment plan, improving health outcomes for men both in terms of endocrine function and overall quality of life.
Medical Disclaimer
This article is intended for general educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. The information presented is based on current scientific literature and clinical understanding at the time of publication, but medical knowledge and guidelines continue to evolve.
Testosterone levels, prolactin disorders, pituitary conditions, and hormone therapies vary significantly between individuals and require personalized evaluation, laboratory testing, and clinical judgment by a qualified healthcare professional. Decisions regarding hormone testing, testosterone therapy, treatment of elevated prolactin, or use of medications such as cabergoline or bromocriptine should always be made in consultation with a licensed physician or other qualified healthcare provider who is familiar with your medical history and individual risk factors.
Do not start, stop, or change any medication or hormone therapy based solely on information from this article. If you are experiencing symptoms such as low libido, erectile dysfunction, infertility, fatigue, breast changes, headaches, or vision problems, seek prompt medical evaluation.
If you have questions about testosterone therapy, prolactin levels, pituitary disorders, or other hormonal conditions, please consult a board-certified physician specializing in endocrinology, urology, or reproductive medicine.
In case of a medical emergency, contact your healthcare provider or emergency services immediately.
References:
- Zeitlin SI, Rajfer J. Hyperprolactinemia and Erectile Dysfunction. Rev Urol. 2000;2(1):39-42[6][74].
- Melmed S, Casanueva FF, Hoffman AR, et al. Diagnosis and Treatment of Hyperprolactinemia: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2011;96(2):273-288[45][42].
- Thrive Men’s Clinic. The 6 Most Important Lab Values to Check for the Diagnosis of Low Testosterone. Men’s Thrive Blog. 2020[3][58].
- Endocrine Society. Hyperprolactinemia – Patient Fact Sheet. January 24, 2022[20][1].
- Gooren LJ, van der Veen EA, et al. Prolactin secretion in the human male is increased by endogenous oestrogens and decreased by exogenous/endogenous androgens. Int J Androl. 1984;7(1):53-60[24][23].
- Ruiz E, et al. Effects of depot testosterone administration on serum levels of testosterone, FSH, LH and prolactin. J Endocrinol Invest. 1980;3(4):385-388[28].
- Dr.Oracle (Medical Q&A Platform). Exogenous Testosterone and Prolactin Levels. 2025[34][26].
- Colao A, et al. Medical therapy for prolactinomas: agents and outcomes. Nat Rev Endocrinol. 2009;5(10):513-520[46][47].
- Pituitary Society. Prolactinoma – Expert Guidance. 2021[39][45].
- Hims Health Blog. Cabergoline for Men: Is It Good for Sexual Health? 2022[50][49].
- Crawford M, Kennedy L. Testosterone replacement therapy: role of pituitary and thyroid in diagnosis and treatment. Transl Androl Urol. 2016;5(6):912-920[75][76].
- Crosnoe LE, et al. Exogenous testosterone: a preventable cause of male infertility. Transl Androl Urol. 2013;2(3):106-113[60][66].
[1] [14] [16] [19] [20] Hyperprolactinemia | Endocrine Society
https://www.endocrine.org/patient-engagement/endocrine-library/hyperprolactinemia
[2] [7] [9] [10] [11] [12] [13] [15] [17] [39] [41] [42] [43] [44] [45] Prolactinoma Treatment – Expert Guidance
https://pituitarysociety.org/prolactinoma
[3] [58] [68] [69] Low Testosterone: the 7 most important lab values to check prior to TRT
[4] [8] [49] [50] [51] [56] Cabergoline for Men: Is It Good for Sexual Health? | Good Health by Hims
https://www.hims.com/blog/cabergoline
[5] [6] [74] Hyperprolactinemia and Erectile Dysfunction – PMC
https://pmc.ncbi.nlm.nih.gov/articles/PMC1476085
[18] [21] [22] [26] [27] [31] [32] [34] [37] [38] [57] Can elevated levels of exogenous testosterone (testosterone replacement therapy) increase prolactin levels?
[23] [24] [25] Prolactin secretion in the human male is increased by endogenous oestrogens and decreased by exogenous/endogenous androgens – PubMed
https://pubmed.ncbi.nlm.nih.gov/6715064
[28] [29] Effects of depot testosterone administration on serum levels of testosterone, FSH, LH and prolactin – PubMed
https://pubmed.ncbi.nlm.nih.gov/6782152
[30] [33] [73] Can testosterone injections cause hyperprolactinemia?
https://www.droracle.ai/articles/429597/can-testosterone-injections-cause-hyperprolactinemia
[35] [36] [40] [46] [47] [48] [52] [53] [54] [55] [67] The Role of Aromatase Inhibitors in Male Prolactinoma – PMC
https://pmc.ncbi.nlm.nih.gov/articles/PMC9962537
[59] Estradiol Testing in Men | myadlm.org
[60] [61] [62] [63] [66] Exogenous testosterone: a preventable cause of male infertility – Crosnoe – Translational Andrology and Urology
https://tau.amegroups.org/article/view/2249/html
[64] Clomiphene Citrate Treatment as an Alternative Therapeutic …
https://pmc.ncbi.nlm.nih.gov/articles/PMC11435126
[65] Testosterone Replacement Therapy Versus Clomiphene Citrate in …
https://www.eu-focus.europeanurology.com/article/S2405-4569%2818%2930217-7/abstract
[70] [PDF] Table 8: Adjunctive Testing
https://www.auanet.org/documents/Guidelines/PDF/Table%20Eight%20-%20Adjunctive%20Testing.pdf
[71] [72] Effect of Chronic Cabergoline Treatment and Testosterone Replacement on Metabolism in Male Patients with Prolactinomas | Neuroendocrinology | Karger Publishers
https://karger.com/nen/article/101/1/66/220078/Effect-of-Chronic-Cabergoline-Treatment-and
[75] [76] Testosterone replacement therapy: role of pituitary and thyroid in diagnosis and treatment – Crawford – Translational Andrology and Urology