Monomeric prolactin is the small (~23 kDa) biologically active form of prolactin produced by pituitary lactotrophs. It drives lactation and influences reproductive and metabolic functions. In blood testing, monomeric prolactin is the clinically relevant fraction—elevated levels cause true hyperprolactinemia with symptoms such as galactorrhea, amenorrhea, and infertility. Larger “macroprolactin” forms are often inactive and can give false-high results.

Doctors order a prolactin test to diagnose or monitor hyperprolactinemia, which can cause irregular menstrual cycles, infertility, unexplained breast milk (galactorrhea), low libido, erectile dysfunction, headaches, or visual changes. It helps detect prolactin-secreting pituitary tumors and assesses effects of medications (e.g., antipsychotics, domperidone). Tests also guide treatment response and further imaging decisions when levels are abnormal.

High monomeric (true) prolactin elevation is caused by prolactin-secreting pituitary adenomas (prolactinomas) or other sellar masses with stalk compression; primary hypothyroidism (via raised TRH); pregnancy and lactation; dopamine-blocking drugs (antipsychotics, metoclopramide, domperidone, some antidepressants, verapamil); chest-wall trauma/stimulation; chronic renal or liver disease; and acute stress or intense exercise.

A prolactin test measures the blood level of prolactin, a pituitary hormone. It’s used to detect high or low prolactin, helping evaluate causes of unexplained breast milk production (galactorrhea), irregular or absent menstrual cycles, infertility, decreased libido or erectile dysfunction, and symptoms suggesting a pituitary tumor. Results also guide treatment monitoring and prompt checks for thyroid disease or medication effects.

To lower monomeric prolactin, address underlying causes: treat hypothyroidism, stop or switch prolactin-raising medications with medical supervision, reduce stress and nipple stimulation, and treat prolactinomas with dopamine agonists (cabergoline or bromocriptine) as directed by a clinician. Confirm levels with repeat testing to exclude macroprolactin and follow specialist advice for imaging and treatment adjustments.

High prolactin in females (hyperprolactinemia) commonly causes irregular or absent periods, infertility, and unwanted milk production (galactorrhea). It lowers estrogen, causing vaginal dryness, decreased libido, and long-term bone loss. Large pituitary tumors may produce headaches and visual changes. Diagnosis uses blood tests and imaging; medical therapy often normalizes levels.