Most men I talk to have heard about testosterone. Some know about oestradiol, DHT, cortisol. Hardly any have heard about prolactin — and that's the problem.
Prolactin is a hormone made by your pituitary gland. Its primary job is to stimulate milk production in women. Men produce it too, in much smaller amounts. And when it gets too high, it quietly tanks your testosterone, your libido, and often your mood without you ever knowing why.
What Prolactin Actually Does
Prolactin is inhibited by dopamine. Your hypothalamus sends dopamine down a portal blood system to your pituitary, which keeps prolactin suppressed. When that dopamine signal weakens — from stress, drugs, or pituitary tumours — prolactin rises.
High prolactin does two things:
- It suppresses GnRH release from your hypothalamus, which shuts down LH and FSH production. Less LH means less testosterone synthesis in the testis.
- It increases dopamine reuptake, creating a negative feedback loop that makes things worse.
The result: low testosterone, often with perfectly normal testosterone that's simply undersaturating your androgen receptors because prolactin is in the way.
Symptoms of High Prolactin (Hyperprolactinaemia)
- Low libido and erectile dysfunction — often the first sign men notice
- Fatigue and low energy, even after sleep
- Mood issues — depression, apathy, low motivation
- Gynecomastia — breast tissue enlargement (usually painless)
- Difficulty with erections despite normal sexual desire
- Brain fog and poor concentration
The tricky part: these overlap completely with symptoms of low testosterone. That's why testing matters.
Common Causes
Pituitary microadenoma. A benign growth that secretes prolactin. More common than you'd think — autopsy studies suggest 10% of men have them. Most are asymptomatic, but some raise prolactin significantly.
Dopamine antagonist drugs. Antipsychotics (risperidone, haloperidol), some antidepressants, metoclopramide (for reflux), and domperidone all raise prolactin by blocking dopamine.
Stress and sleep deprivation. Chronic stress and poor sleep blunt dopamine signalling.
Hypothyroidism. Low thyroid function can raise prolactin slightly.
Idiopathic hyperprolactinaemia. High prolactin with no clear cause. Usually mild.
How to Test
Ask your GP or private provider for serum prolactin. Ideally fasting, and taken in the morning (prolactin is highest early morning, drops through the day).
UK reference ranges vary slightly by lab, but typically:
- Men: <20 mIU/L (some labs use <15 mIU/L)
- Values 20-50 mIU/L are often considered "borderline" and warrant rechecking and investigation
- Values >50 mIU/L are clearly elevated
If you're using Medichecks or a similar private service, order their hormone panel — it includes prolactin along with testosterone, LH, and FSH.
What to Do If It's Elevated
First: rule out medication. If you're on any dopamine antagonist, talk to your doctor about switching. This solves the problem in many cases.
If it's a microadenoma or idiopathic: Your doctor will usually start with a dopamine agonist.
- Cabergoline (Dostinex): 0.25–0.5 mg twice weekly. More potent and better tolerated than bromocriptine. Often normalises prolactin quickly. Side effects are rare but can include nausea, dizziness, and rarely valvular problems (with long-term high-dose use, which is uncommon).
- Bromocriptine: Older, more side effects (nausea, dizziness), but also effective. 1.25–2.5 mg daily to start.
Most men see improvements in libido, mood, and energy within 2–4 weeks once prolactin normalises.
If it's your thyroid: Fix the thyroid first — prolactin will often come down with it.
When to Refer
If your prolactin is consistently >100 mIU/L, or if you have symptoms and prolactin is >50 mIU/L, ask your GP for an MRI of your pituitary gland. This rules out adenoma and guides treatment.
Endocrinology referral is warranted if:
- Prolactin remains high despite dopamine agonist treatment
- You have headaches or vision problems (pituitary tumour symptoms)
- Prolactin is very high (>200 mIU/L)
The Bottom Line
High prolactin is an often-missed cause of low testosterone symptoms in men. It's easy to test for, and treatment is straightforward. If you're experiencing low libido, ED, fatigue, or mood issues alongside any reason to suspect low testosterone, ask for prolactin to be tested. It's a single blood test that could explain everything.
Use Medichecks to test it yourself if your GP won't. Most cases resolve quickly once prolactin is normalised.