Prolactin is a hormone produced by the pituitary gland, a small structure at the base of the brain. It is best known for its role in stimulating breast milk production after childbirth, but it also influences reproductive function, immune regulation, and metabolism in both women and men.
Outside of pregnancy and breastfeeding, prolactin circulates at relatively low levels. When it becomes persistently elevated (a condition called hyperprolactinaemia), it can suppress the hormonal signals that trigger ovulation. In women, this often presents as irregular or absent periods, unexpected nipple discharge (galactorrhoea), and difficulty conceiving. In men, elevated prolactin can reduce testosterone levels, leading to decreased libido, erectile dysfunction, and in some cases gynaecomastia.
The most common cause of persistent hyperprolactinaemia is a prolactinoma, a small benign tumour of the pituitary gland. These are the most common type of pituitary tumour and generally respond well to medication. Other causes include certain medications (particularly antipsychotics, anti-nausea drugs, and some antidepressants), hypothyroidism, and kidney disease. Identifying the underlying cause is important because the treatment approach differs depending on what is driving the elevation.
One of the distinctive features of prolactin is how sensitive it is to stress and physical activity. Even mild anxiety, a brisk walk to the pathology centre, or nipple stimulation can temporarily spike prolactin levels. For this reason, a 30-minute rest in a calm environment before your blood draw is not optional for this test. Without it, a falsely elevated result may trigger unnecessary further investigation. If a first result comes back mildly elevated, practitioners will often repeat it under stricter resting conditions before pursuing imaging or other investigations.
Suited to women with irregular or absent menstrual cycles, unexplained fertility difficulties, or nipple discharge not related to pregnancy or breastfeeding. Also relevant for men with reduced libido, gynaecomastia, or unexplained infertility where a pituitary cause is being considered.
