Breastfeeding requires stimulation from high prolactin levels, which also stops menstrual cycles and eliminates the possibility of getting pregnant while focusing the mother’s energy on milk production for the baby. Prolactin affects both sexes and normal levels are:

• Below 500 mIU/l for women
• Below 450 mIU/l for men

Men with hyperprolactinaemia get changes to their breast tissue and express milk, and the elevated hormone levels also cause erectile dysfunction and low libido, which can make them infertile. For women, the signs of hyperprolactinaemia are:

• Breast tenderness and a spontaneous flow of milk outside pregnancy
• Abnormal menstrual cycles (with low estrogen levels)
• Infertility

How it works

• The anterior pituitary makes prolactin, and it also produces FSH and LH, which stimulate the ovaries to start new cycles and trigger ovulation.
• Prolactin levels are high in late pregnancy, and while breastfeeding to focus the mother’s energy on milk production for her baby.
• The high prolactin level prevents GnRH from being released from the hypothalamus, which will start new menstrual cycles.
• Hyperprolactinaemia involves inappropriately high prolactin levels outside pregnancy, which blocks GnRH release and causes infertility.

5 Organic causes of hyperprolactinaemia

1. During pregnancy and breastfeeding (normal).
2. Some hypothalamic or pituitary gland diseases, which are usually small benign growths (under 10mm) on the pituitary gland called “microadenomas”.
3. Some drugs, medicinal herbs and heavy metals can disrupt prolactin and dopamine levels. Dopamine is a "feel good" brain chemical that also controls prolactin levels. Low dopamine levels cause prolactin levels to rise.
4. Mental stress can bring on hyperprolactinaemia by disrupting the hypothalamus-pituitary-gonad (HPG) axis, as the hypothalamus is the link between the autonomic nervous and hormonal systems.
5. Diseases of other organs (the liver, kidneys, ovaries and thyroid) are less common, but they can also cause hyperprolactinaemia. ⁱ

Drug causes of hyperprolactinaemia

Hyperprolactinaemia can be triggered by drugs that alter dopamine levels (it's a neurotransmitter). Dopamine is essential for memory, movement, pleasure, thinking, and sleep, and it’s a significant issue in Parkinson’s disease. Dopamine controls prolactin production, and there are two types of drugs that can cause problems:

1. Drugs that block the effect of dopamine in the pituitary
2. Drugs that deplete dopamine stores in the brain
   • These include the major tranquillizers such as phenothiazines, haloperidol and trifluoperazine (generally antipsychotic drugs).
   • The "dopamine-antagonists"; metoclopramide and domperidone cause high prolactin levels and have been used to stimulate lactation for decades.
   • Anti-reflux medicines such as cisapride and metoclopramide and the sleep agent ramelteon also cause hyperprolactinaemia.

Since prolactin is controlled by dopamine, and the body depends on the two being in balance, the risk of hyperprolactinaemia is present with all drugs that deplete dopamine, either directly or as a rebound effect.

Diagnosis

• A serum prolactin concentration over 1000 mIU/l is diagnostic, and a second test should be done to confirm the diagnosis.
• Luteinizing hormone (LH) and stimulating follicle hormone (FSH) are usually at the lower end of the normal range (along with a low estradiol concentration).
• An MRI scan is needed to confirm if a microadenoma is on the pituitary.
• Patients with a microadenoma should have their vision checked thoroughly because the enlarged pituitary may be pressing on the optic chiasm (where the optic nerves cross in the brain).