Prolactin

Prolactin is a hormone produced by the pituitary gland, best known for stimulating breast milk production after childbirth. But prolactin does much more — and when elevated outside of pregnancy and breastfeeding, it can disrupt reproductive function in both women and men. High prolactin suppresses the hormones needed for ovulation and testosterone production, making it a common and treatable cause of infertility.

Why does this matter? Elevated prolactin (hyperprolactinemia) is one of the most common hormonal disorders affecting reproduction. It can cause irregular or absent periods, infertility, unwanted breast milk production (galactorrhea), and sexual dysfunction. In men, it causes low testosterone, erectile dysfunction, and sometimes breast enlargement. The good news: once identified, hyperprolactinemia is usually very treatable with medication. Prolactin testing uncovers this hidden cause of reproductive problems.

Order Your Prolactin Test

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Key Benefits of Testing

Prolactin testing identifies hyperprolactinemia — a common, treatable cause of menstrual irregularities, infertility, and sexual dysfunction. Because elevated prolactin suppresses reproductive hormones, it can mimic other conditions and is easily missed without specific testing.

Testing also screens for pituitary tumors. Prolactinomas (prolactin-secreting pituitary tumors) are the most common type of pituitary tumor and are usually benign. They’re often discovered through prolactin testing prompted by symptoms. Early detection allows treatment before tumors grow large enough to cause headaches or vision problems.

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What Does This Test Measure?

The prolactin test measures the concentration of prolactin hormone in your blood. Prolactin is produced primarily by lactotroph cells in the anterior pituitary gland. Unlike most pituitary hormones, prolactin secretion is tonically inhibited by dopamine from the hypothalamus — meaning dopamine normally keeps prolactin levels low. Anything that reduces dopamine’s inhibitory effect can raise prolactin.

What Prolactin Does

Prolactin’s primary role is stimulating breast milk production (lactation). During pregnancy, prolactin levels rise dramatically, preparing the breasts for milk production. After delivery, suckling stimulates prolactin release, maintaining milk supply. High prolactin during breastfeeding also suppresses ovulation, providing natural (though imperfect) contraception.

Beyond lactation, prolactin has effects throughout the body. It influences immune function, metabolism, and behavior. In the reproductive system, elevated prolactin suppresses gonadotropin-releasing hormone (GnRH), which in turn reduces FSH and LH, leading to decreased estrogen in women and decreased testosterone in men.

Prolactin Regulation

Dopamine from the hypothalamus continuously inhibits prolactin secretion. This is unique — most pituitary hormones are stimulated by hypothalamic releasing hormones, but prolactin is held in check by an inhibiting signal. When dopamine signaling is disrupted (by tumors, medications, or other factors), prolactin rises. This understanding is therapeutically important: dopamine-enhancing medications effectively lower prolactin.

Normal Variations

Prolactin levels fluctuate throughout the day, with highest levels during sleep and lowest in mid-morning. Stress, exercise, nipple stimulation, and meals can temporarily raise prolactin. For accurate testing, blood should be drawn in a non-stressed state, ideally mid-morning, and not immediately after breast examination.

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Why This Test Matters

For Women

Evaluates menstrual irregularities. Elevated prolactin is a common cause of irregular or absent periods. By suppressing GnRH, high prolactin reduces FSH and LH, disrupting normal ovulation. Prolactin testing is standard in the evaluation of amenorrhea or oligomenorrhea.

Investigates infertility. Even mildly elevated prolactin can interfere with ovulation. Hyperprolactinemia is one of the most treatable causes of infertility — medication normalizes prolactin in most cases, restoring ovulation and fertility.

Explains galactorrhea. Inappropriate breast milk production (outside of pregnancy and breastfeeding) is often caused by elevated prolactin. Testing confirms the diagnosis and prompts evaluation for underlying causes.

For Men

Evaluates low testosterone symptoms. Elevated prolactin suppresses testosterone production, causing fatigue, decreased libido, erectile dysfunction, and sometimes infertility. Men with these symptoms and low testosterone should have prolactin checked to identify this treatable cause.

Investigates gynecomastia and galactorrhea. While less common than in women, men with elevated prolactin can develop breast enlargement or even milk production. Prolactin testing is part of the evaluation.

Screens for pituitary tumors. Prolactinomas can occur in men, often presenting later with larger tumors because early symptoms (low libido, erectile dysfunction) may be attributed to other causes. Very high prolactin levels strongly suggest prolactinoma.

Screens for Pituitary Tumors

Prolactinomas are the most common functioning pituitary tumor. They range from tiny microadenomas (under 10mm) to large macroadenomas. Very high prolactin levels generally correlate with tumor size — moderately elevated prolactin might indicate a small tumor or other causes, while very high levels strongly suggest a larger prolactinoma. Identifying these tumors matters because they’re highly treatable with medication and rarely require surgery.

Value of Early Testing

Prolactin elevation can develop silently, with subtle symptoms easily attributed to stress or aging. Women with gradually lengthening cycles or difficulty conceiving benefit from early prolactin testing before months of frustration. Men with declining libido or energy often don’t think to mention these symptoms — but when they do, prolactin testing can uncover a readily treatable cause. Because treatment is so effective, identifying hyperprolactinemia early can quickly restore quality of life and fertility.

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What Can Affect Prolactin Levels?

Causes of Elevated Prolactin

Physiological causes (normal elevations):

• Pregnancy — prolactin rises significantly
• Breastfeeding — suckling stimulates prolactin
• Stress — acute stress temporarily raises prolactin
• Sleep — prolactin peaks during sleep
• Nipple stimulation or breast examination
• Sexual activity

Medications (common cause):

• Antipsychotics — especially older typical antipsychotics, but also many atypicals
• Metoclopramide and domperidone (anti-nausea medications)
• Some antidepressants (SSRIs, tricyclics)
• Opioids
• Estrogen-containing medications (high-dose)
• Some blood pressure medications (verapamil, methyldopa)

Pituitary causes:

• Prolactinoma — prolactin-secreting pituitary tumor
• Other pituitary tumors compressing the stalk (disrupting dopamine delivery)
• Empty sella syndrome
• Pituitary surgery or radiation effects

Other medical conditions:

• Hypothyroidism — elevated TRH stimulates prolactin
• Chronic kidney disease — reduced prolactin clearance
• Liver cirrhosis
• Chest wall irritation or injury (nerve pathways to hypothalamus)
• Polycystic ovary syndrome (mild elevation in some cases)

Causes of Low Prolactin

Low prolactin is uncommon and usually not clinically significant. It may occur with pituitary damage affecting lactotroph cells or with dopamine agonist medication use. The main consequence is inability to breastfeed after delivery.

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When Should You Get Tested?

For Women

Irregular or absent menstrual periods — prolactin is part of standard amenorrhea workup.

Infertility evaluation — especially with menstrual irregularities or unexplained infertility.

Galactorrhea — breast milk production outside of pregnancy and nursing.

Symptoms suggesting pituitary tumor — headaches, visual changes, combined with any of the above.

For Men

Low testosterone with unclear cause — especially if FSH and LH are also low (suggesting secondary hypogonadism).

Sexual dysfunction — decreased libido, erectile dysfunction, particularly if not responding to typical treatments.

Gynecomastia or galactorrhea — breast enlargement or milk production.

Infertility — as part of hormonal evaluation.

For Both Sexes

Symptoms suggesting pituitary mass — unexplained headaches, visual field changes.

Before and during treatment — monitoring response to prolactin-lowering medications.

Order Your Test

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Understanding Your Results

Prolactin interpretation considers the degree of elevation, symptoms, medication use, and clinical context.

Normal prolactin effectively rules out hyperprolactinemia as a cause of symptoms. If symptoms strongly suggest prolactin-related problems, consider whether stress or timing affected the result — repeat testing in optimal conditions may be warranted.

Mildly elevated prolactin has many potential causes including stress, medications, hypothyroidism, and small prolactinomas. Repeat testing to confirm (excluding stress effect), review medications, and check thyroid function. Mild elevation may or may not require treatment depending on symptoms.

Moderately elevated prolactin increases suspicion for prolactinoma or significant medication effect. After excluding medications and hypothyroidism, pituitary MRI is typically indicated to evaluate for tumor.

Very high prolactin strongly suggests prolactinoma. The higher the level, the larger the likely tumor. Pituitary MRI is essential. Very high levels with only a small tumor visible, or high levels with no tumor, should prompt evaluation for “hook effect” (a lab artifact with very high prolactin) by testing a diluted sample.

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What to Do About Abnormal Results

For Elevated Prolactin

Confirm the elevation. Repeat testing in non-stressed conditions if stress might have affected results.

Review medications. Many drugs raise prolactin. If a medication cause is identified, discuss alternatives with your prescriber when appropriate.

Check thyroid function. Hypothyroidism elevates prolactin and is easily treatable — correcting thyroid levels normalizes prolactin.

Consider pituitary imaging. If prolactin is significantly elevated without obvious medication or thyroid cause, MRI of the pituitary evaluates for prolactinoma or other pituitary lesions.

Treatment options depend on the cause:

• Prolactinoma: Dopamine agonist medications (cabergoline, bromocriptine) are first-line treatment and are highly effective at shrinking tumors and normalizing prolactin. Surgery is rarely needed.
• Medication-induced: Switch to alternatives that don’t raise prolactin when possible. If not possible, dopamine agonists may be considered.
• Hypothyroidism: Thyroid hormone replacement normalizes prolactin.
• Idiopathic: When no cause is found, treatment depends on symptoms and fertility goals.

For Normal Prolactin with Galactorrhea

Galactorrhea can occasionally occur with normal prolactin, particularly if caused by prior prolactin elevation that has normalized or breast hypersensitivity. Other causes should be considered.

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Related Health Conditions

Prolactinoma

Prolactinomas are benign pituitary tumors that secrete prolactin. They’re the most common type of pituitary tumor and cause hyperprolactinemia with its associated symptoms — menstrual disruption, infertility, galactorrhea, and in men, low testosterone. Treatment with dopamine agonists is highly effective, shrinking tumors and normalizing prolactin in most patients. Surgery is rarely required.

Hyperprolactinemia

Elevated prolactin from any cause — tumors, medications, hypothyroidism, or idiopathic — produces similar symptoms by suppressing reproductive hormones. In women: irregular periods, infertility, galactorrhea. In men: low testosterone, sexual dysfunction, infertility. Treatment targets the underlying cause when possible.

Secondary Amenorrhea

When periods stop in a woman who previously menstruated, hyperprolactinemia is one of the key causes to evaluate. Elevated prolactin suppresses GnRH, leading to low FSH and LH and consequently low estrogen and anovulation. Prolactin testing is standard in amenorrhea workup.

Infertility

Hyperprolactinemia is a common and highly treatable cause of infertility in both women and men. In women, it prevents ovulation. In men, it suppresses testosterone and may impair sperm production. Normalizing prolactin with medication often restores fertility without need for assisted reproduction.

Male Hypogonadism

Elevated prolactin suppresses LH, reducing testosterone production — a form of secondary hypogonadism. Men may present with fatigue, low libido, and erectile dysfunction. Checking prolactin is important because treating the hyperprolactinemia can restore testosterone naturally, unlike simply replacing testosterone.

Hypothyroidism

Hypothyroidism can cause elevated prolactin through increased TRH (thyrotropin-releasing hormone), which stimulates both TSH and prolactin. This is important to identify because treating hypothyroidism normalizes prolactin — no specific prolactin treatment is needed. Always check thyroid function when prolactin is elevated.

Galactorrhea

Inappropriate breast milk production outside of pregnancy and breastfeeding is often caused by elevated prolactin. It can occur in both women and (rarely) men. While sometimes distressing, galactorrhea itself is not dangerous — the concern is identifying the underlying cause of elevated prolactin.

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Related Biomarkers Often Tested Together

TSH — Hypothyroidism causes elevated prolactin; always check thyroid function.

FSH and LH — Often suppressed by elevated prolactin; help assess reproductive axis.

Estradiol — Low in women with hyperprolactinemia-induced amenorrhea.

Testosterone — Low in men with hyperprolactinemia.

IGF-1 — If pituitary tumor suspected, screens for growth hormone co-secretion.

Note: Information provided in this article is for educational purposes and doesn’t replace personalized medical advice.