Prolactin

Prolactin comes from the pituitary, the gland beneath your brain that also releases LH and FSH. Its best-known task is milk production after childbirth: during pregnancy it climbs, and as long as a baby feeds it stays high. At the same time it puts the cycle on hold, and that is not a side effect but the intention: a high prolactin suppresses the release of LH and FSH, so that the ovaries rest for as long as there is breastfeeding. That brake is also the reason prolactin is measured outside breastfeeding. A prolactin that sits too high without pregnancy or breastfeeding does the same: in women the cycle becomes irregular or stays away, sometimes with milk secretion, in men LH and testosterone fall, with less desire and sometimes breast tissue as the result. Prolactin is therefore one of the first values looked at with a missing cycle, an unexplained low testosterone or little desire. Your report shows prolactin in mIU/L, at some labs written as mE/l or, a thousand times smaller, in U/l; it is the same quantity. The range sits slightly higher in women than in men, because oestrogen drives production, and it falls in women after the menopause. Normal is 86 to 278 mIU/L in men and 105 to 496 mIU/L in women up to 50 years, where the labs overlap.

Prolactin is a hormone that moves within the day itself. It rises during sleep and is still high in the first hours after waking, it rises with stress, pain, exertion and sex, with a meal, and even with the draw itself. A slightly raised value is therefore usually a moment and not a level, and is first repeated at rest: in the morning, a few hours after getting up, rested, and not after exercise or sex. If it stays raised, there are three usual explanations. The first is medicines: anti-nausea drugs such as metoclopramide and domperidone, many antipsychotics and some antidepressants block dopamine, the brake on prolactin, and lift it sharply. The second is an underactive thyroid, because the hormone that drives the thyroid also drives prolactin; TSH shows it. The third is a prolactinoma, a benign nodule in the pituitary that makes prolactin. That sounds more serious than it is: it is the most common pituitary tumour, almost always benign, and usually treatable with tablets that shrink the prolactin and the nodule together. There is a fourth, harmless explanation: macroprolactin, a large form of the hormone that counts in the measurement but does nothing. It can be tested for, and with a raised prolactin without complaints that is the first question. Lifestyle is not a big lever for prolactin, apart from two things: sleep and stress. Anyone who structurally sleeps too little or lives under lasting stress measures higher values, and that carries through into the cycle and desire. Beyond that, prolactin is above all a value to measure well and read well.

A raised prolactin starts with the question of how the measurement went: shortly after waking, after exertion, sex, a meal or a stressful draw, then a repeat at rest is the first step. If it stays slightly to moderately raised, medicines that block dopamine, an underactive thyroid, pregnancy and macroprolactin are the usual explanations, in that order. A strongly raised value, a multiple of the range, fits a prolactinoma, and then an MRI of the pituitary belongs to it. In women a missing cycle or milk secretion comes with it, in men a low testosterone. A low prolactin almost never means anything. It occurs with medicines that mimic dopamine, such as drugs for Parkinson's disease and the tablets for a prolactinoma, and very rarely with a pituitary that makes too little as a whole; then other pituitary hormones are abnormal too. What you can do yourself is make the measurement clean and know the levers there are: enough sleep, less lasting stress, and with a raised value checking which medicines you take, because that is where the most common reversible cause sits. A prolactinoma or an underactive thyroid are very treatable, and the cycle and testosterone then return. Read prolactin beside LH and FSH, the hormones it suppresses, beside oestradiol or testosterone, the consequence of that, and beside TSH, because an underactive thyroid raises it. Compare over time in the same unit and at the same lab.