Prolactin

What it measures.

Prolactin is a pituitary hormone primarily responsible for breast milk production, but chronically elevated levels outside of pregnancy and lactation are one of the most common and treatable causes of anovulatory infertility — accounting for approximately 15-20% of female infertility cases. Hyperprolactinaemia suppresses GnRH pulsatility, reducing FSH and LH, which impairs ovulation and testosterone production.

Serum prolactin concentration reflecting pituitary lactotroph output. Prolactin is regulated by dopaminergic inhibition from the hypothalamus — dopamine tonically suppresses prolactin release. Any disruption of this pathway raises prolactin.

Why it matters.

Even mild elevation (25-50 ng/mL) causes luteal insufficiency and can contribute to recurrent miscarriage. Moderate elevation (50-200 ng/mL) typically causes amenorrhoea and anovulation. Severe elevation (>200 ng/mL) almost always indicates a pituitary prolactinoma requiring imaging. Critically, hyperprolactinaemia is highly treatable — dopamine agonists normalise prolactin and restore fertility in the majority of cases.

Physiology.

Prolactin is produced by lactotroph cells in the anterior pituitary. Unlike other pituitary hormones, it is under tonic inhibition (not stimulation). Hypothalamic dopamine continuously suppresses prolactin release. Anything that reduces dopamine delivery (pituitary tumours compressing the stalk, medications blocking dopamine receptors) raises prolactin. High prolactin suppresses GnRH neurons, reducing LH/FSH pulsatility.

Testing & preparation.

How to prepare

• Draw fasting, in a relaxed state
• Avoid breast stimulation for 24 hours before testing
• Avoid vigorous exercise for 24 hours before testing
• Morning draw preferred
• A single elevated value should ALWAYS be repeated before treatment

When to test

Irregular or absent periods, galactorrhoea (nipple discharge), unexplained infertility, low testosterone in men with low/normal LH, suspected pituitary disorder.

How often

Repeat if initially elevated (to confirm). Monitor every 3-6 months on dopamine agonist therapy.

Interpretation.

High prolactin

Common causes:

• Medications: antipsychotics, metoclopramide, SSRIs, opioids (most common cause)
• Prolactinoma (pituitary adenoma — micro or macro)
• Primary hypothyroidism (elevated TRH stimulates prolactin)
• Stress, food, or exercise artifact (physiological, transient)
• Pituitary stalk compression (any sellar/parasellar mass)
• Macroprolactinaemia (biologically inactive big-prolactin — false positive)

Implications:

• Mild (25-50 ng/mL): luteal insufficiency, subfertility, needs repeat confirmation
• Moderate (50-200 ng/mL): amenorrhoea, anovulation, rule out medications and hypothyroidism
• Severe (>200 ng/mL): almost always prolactinoma — pituitary MRI indicated
• Men: hypogonadism, reduced libido, erectile dysfunction, rarely galactorrhoea

Low prolactin

Common causes:

• Clinically rare and usually insignificant
• Sheehan syndrome (postpartum pituitary infarction)
• Dopamine agonist therapy (therapeutic goal)

Implications:

• Low prolactin is not a fertility concern
• May indicate broader pituitary insufficiency if other hormones are also low

Optimization.

Diet

• No specific dietary interventions for hyperprolactinaemia
• Adequate iodine and selenium for thyroid health (hypothyroidism raises prolactin)

Lifestyle

• Stress reduction — stress can transiently elevate prolactin
• Review medications with your provider (antipsychotics are the most common drug cause)
• Adequate sleep supports normal prolactin rhythm

Supplements

• Vitex agnus-castus (chasteberry) has dopaminergic activity — some evidence for mild hyperprolactinaemia
• Not a substitute for dopamine agonist therapy when clinically indicated

FAQs.