When you hear the word prolactin, you might immediately think of pregnancy and breastfeeding. And you would be partially correct. But prolactin—a hormone produced by the pituitary gland—does far more than most people realize. It influences fertility, bone health, metabolism, immune function, and even behavior.
Understanding what is prolactin is essential for anyone experiencing unexplained infertility, irregular periods, breast discharge, or low libido. When prolactin levels become abnormal—specifically when there is a high level of prolactin hormone—the effects can ripple throughout the entire body.
This article explains everything you need to know: what are prolactin (yes, there are multiple forms), how the prolactin hormone works, what causes elevated prolactin, how to interpret a prolactin blood test, and what treatments are available for high prolactin levels.
Part 1: What Is Prolactin? Defining the Hormone
To answer what is prolactin, we must start with the basics. Prolactin (abbreviated PRL) is a peptide hormone produced primarily by the anterior pituitary gland—a pea-sized organ at the base of the brain. Small amounts are also produced by the uterus, breast tissue, immune cells, and even the brain itself.
The name prolactin comes from “pro-” (promoting) and “lactin” (milk). Its most famous job is stimulating lactation—milk production—after childbirth. But prolactin is present in both women and men, and it serves many other functions.
What Are Prolactin? The Different Forms
When scientists ask what are prolactin, they are often referring to the different molecular forms of the hormone circulating in the blood:
| Form | Description | Clinical Significance |
|---|---|---|
| Monomeric prolactin (little prolactin) | The biologically active form; molecular weight ~23 kDa | This is what most prolactin blood tests measure. Elevated levels cause symptoms. |
| Big prolactin | A dimer (two molecules bound together); weight ~50 kDa | Less biologically active; may be elevated without causing symptoms. |
| Big-big prolactin (macroprolactin) | A large complex of prolactin bound to an antibody; weight ~150 kDa | Biologically inactive. Macroprolactinemia is a benign condition where prolactin levels appear high on standard tests but cause no symptoms. |
Important clinical pearl: Up to 15-20% of people with high prolactin levels on routine testing actually have macroprolactinemia—a harmless laboratory artifact. A specialized test (polyethylene glycol precipitation) can distinguish true elevated prolactin from macroprolactin.
Part 2: The Prolactin Hormone – Normal Functions in the Body
The prolactin hormone is remarkably versatile. Here is what it does in both women and men.
In Women
| Function | Mechanism |
|---|---|
| Breast development | Works with estrogen and progesterone to develop breast tissue during puberty |
| Lactation | Stimulates milk production after childbirth. Prolactin levels rise dramatically during pregnancy and remain elevated while breastfeeding. |
| Suppression of ovulation | High prolactin inhibits gonadotropin-releasing hormone (GnRH), which suppresses estrogen and progesterone. This is why many breastfeeding women do not menstruate (lactational amenorrhea). |
| Immune modulation | Prolactin influences immune cell activity; links to autoimmune diseases are being studied. |
| Bone health | May affect bone density, though the mechanism is not fully understood. |
In Men
| Function | Mechanism |
|---|---|
| Testosterone regulation | Prolactin modulates luteinizing hormone (LH), which stimulates testosterone production. |
| Sperm production | Normal prolactin levels are required for spermatogenesis. |
| Sexual function | High prolactin levels are a common cause of low libido and erectile dysfunction. |
| Immune function | Similar immunomodulatory roles as in women. |
In Both Sexes
- Stress response: Prolactin rises with physical and psychological stress.
- Metabolism: May influence insulin sensitivity and fat storage.
- Osmoregulation: Plays a role in fluid and electrolyte balance.
Part 3: Normal Prolactin Levels – What Is Healthy?
Prolactin levels vary by sex, age, and time of day. Prolactin follows a circadian rhythm, peaking during sleep (around 2-5 AM) and reaching its lowest point in the late morning.
Reference Ranges (Typical, Lab-dependent)
| Population | Normal Prolactin Levels (ng/mL) |
|---|---|
| Non-pregnant women | 4 – 23 ng/mL |
| Pregnant women | 30 – 400 ng/mL (rises progressively) |
| Men | 3 – 15 ng/mL |
| Children | 3 – 20 ng/mL |
Important notes:
- Levels above 25 ng/mL in women or 15 ng/mL in men are generally considered high prolactin levels (hyperprolactinemia).
- Mild elevation (25-50 ng/mL) may be caused by medications, stress, or benign conditions.
- Moderate elevation (50-100 ng/mL) suggests a pituitary tumor (prolactinoma) or other organic cause.
- Marked elevation (> 200 ng/mL) is almost always due to a prolactin-secreting macroadenoma.
Part 4: High Prolactin Levels – Causes of Elevated Prolactin
Elevated prolactin (hyperprolactinemia) is surprisingly common. Causes fall into several categories.
1. Physiological (Normal, Temporary)
These causes of high level of prolactin hormone are not diseases and resolve on their own:
| Cause | Mechanism |
|---|---|
| Pregnancy | Prolactin levels rise progressively to prepare the breasts for lactation. |
| Breastfeeding | Nipple stimulation triggers prolactin release. Levels remain high as long as breastfeeding continues frequently. |
| Sleep | Prolactin peaks during deep sleep (REM sleep). |
| Stress (physical or emotional) | Stress hormones (cortisol, TRH) stimulate prolactin release. |
| Exercise | Intense physical activity can transiently raise prolactin. |
| Sexual intercourse | Orgasm is associated with a temporary prolactin surge (more pronounced in women). |
| Nipple stimulation | Even without breastfeeding, nipple manipulation can raise prolactin. |
2. Medication-Induced (Very Common)
Dozens of medications cause high prolactin levels by blocking dopamine (the natural inhibitor of prolactin). This is the most common cause of elevated prolactin in clinical practice.
| Drug Class | Examples | Mechanism |
|---|---|---|
| Antipsychotics (typical and atypical) | Risperidone, haloperidol, paliperidone (highest risk); olanzapine, quetiapine (lower risk) | Dopamine D2 receptor blockade |
| Antidepressants (some) | SSRIs (especially paroxetine, sertraline); tricyclics (amitriptyline); MAOIs | Mild dopamine antagonism |
| Antiemetics | Metoclopramide (Reglan), domperidone (Motilium) | Potent D2 antagonists |
| Antihypertensives | Verapamil, methyldopa, reserpine | Unknown; possibly central dopamine depletion |
| Opiates | Morphine, heroin, methadone, oxycodone | Suppress dopamine release |
| Hormones | Estrogen (oral contraceptives, HRT), antiandrogens | Estrogen stimulates lactotroph cells |
| Proton pump inhibitors (rare) | Omeprazole, esomeprazole | Mechanism unclear |
| H2 blockers (rare) | Cimetidine | Weak dopamine antagonism |
3. Pituitary and Hypothalamic Disorders
| Condition | Mechanism | Typical Prolactin Level |
|---|---|---|
| Prolactinoma (prolactin-secreting pituitary adenoma) | Benign tumor of lactotroph cells; most common pituitary tumor | Microprolactinoma (<1 cm): 50-200 ng/mL; Macroprolactinoma (>1 cm): >200 ng/mL |
| Hypothalamic disease (tumor, sarcoidosis, radiation) | Disruption of dopamine delivery from hypothalamus to pituitary | Mild to moderate elevation |
| Empty sella syndrome | Pituitary gland is flattened; stalk compression reduces dopamine | Mild elevation |
| Pituitary stalk compression (any mass) | Blocks dopamine transport | Mild to moderate elevation |
| Lymphocytic hypophysitis | Autoimmune inflammation of pituitary | Variable |
4. Other Medical Conditions
| Condition | Mechanism |
|---|---|
| Hypothyroidism (underactive thyroid) | High TRH (thyrotropin-releasing hormone) stimulates both TSH and prolactin. Treating hypothyroidism often normalizes prolactin levels. |
| Chronic kidney disease (CKD) | Reduced clearance of prolactin; also altered dopamine metabolism |
| Liver disease (cirrhosis) | Impaired prolactin metabolism; increased estrogen |
| PCOS (Polycystic Ovary Syndrome) | Mild elevated prolactin in some women; mechanism unclear |
| Chest wall trauma or surgery | Irritation of intercostal nerves stimulates prolactin release |
| Spinal cord injury | Disrupted hypothalamic-pituitary regulation |
| Herpes zoster (shingles) of chest wall | Neural irritation |
| Idiopathic hyperprolactinemia | No identifiable cause; likely microadenomas too small to image or functional dysregulation |
Part 5: Symptoms of High Prolactin Levels
The symptoms of high prolactin levels depend on sex, degree of elevation, and duration.
Symptoms in Women
| Symptom | Why It Happens |
|---|---|
| Galactorrhea (milky nipple discharge, not associated with breastfeeding) | Direct stimulation of breast tissue by prolactin |
| Irregular or absent periods (oligomenorrhea or amenorrhea) | High prolactin suppresses GnRH → low estrogen → anovulation |
| Infertility | Lack of ovulation |
| Decreased libido | Low estrogen; direct CNS effects |
| Vaginal dryness | Low estrogen |
| Acne and hirsutism (mild, in some women) | Prolactin may increase adrenal androgens |
| Headaches and visual disturbances (if macroprolactinoma) | Tumor compresses optic chiasm or surrounding structures |
| Osteoporosis (long-standing) | Chronic low estrogen leads to bone loss |
Symptoms in Men
| Symptom | Why It Happens |
|---|---|
| Erectile dysfunction | High prolactin suppresses testosterone |
| Decreased libido | Low testosterone |
| Infertility (low sperm count, poor motility) | Prolactin impairs spermatogenesis |
| Galactorrhea (rare in men, but possible) | Direct breast stimulation |
| Gynecomastia (breast enlargement) | Low testosterone relative to estrogen |
| Headaches and visual disturbances (if macroprolactinoma) | Tumor mass effect |
| Osteoporosis | Chronic low testosterone leads to bone loss |
| Delayed puberty (in adolescent males) | Elevated prolactin inhibits pubertal development |
Symptoms in Both Sexes
| Symptom | Notes |
|---|---|
| Headaches | Common with pituitary tumors |
| Visual field defects (bitemporal hemianopsia) | Optic chiasm compression from macroadenoma |
| Fatigue | Non-specific but common |
| Weight gain | Possible metabolic effects |
| Mood changes (depression, anxiety) | Prolactin and mood regulation are linked |
Part 6: The Prolactin Blood Test – What to Expect
If you have symptoms of high prolactin levels, your doctor will order a prolactin blood test. This is a simple blood draw, but proper preparation is essential to avoid false positives.
How to Prepare for a Prolactin Blood Test
| Recommendation | Why |
|---|---|
| Draw blood in the morning (8-10 AM) | Prolactin is lowest in late morning; avoids the natural sleep peak. |
| Do not breastfeed for 12 hours before | Nipple stimulation raises prolactin. |
| Avoid breast or nipple stimulation for 24 hours | Includes sexual activity, self-exam, or clothing friction. |
| Avoid vigorous exercise the morning of the test | Exercise transiently increases prolactin. |
| Fast overnight (optional but recommended) | Reduces meal-related variations. |
| Rest quietly for 20-30 minutes before the draw | Stress of venipuncture itself can raise prolactin. Having blood drawn after a stressful walk to the lab can falsely elevate results. |
| List all medications (including over-the-counter and supplements) | Many drugs cause high prolactin levels. |
| Avoid breast examination on the same day | Physical stimulation of breasts releases prolactin. |
Interpreting the Prolactin Blood Test
| Result (ng/mL) | Interpretation | Next Steps |
|---|---|---|
| < 25 (women) or < 15 (men) | Normal | No further action unless strong clinical suspicion |
| 25 – 50 | Mild elevated prolactin | Repeat test with careful preparation; check medications, thyroid function (TSH), pregnancy test |
| 50 – 100 | Moderate high prolactin levels | MRI pituitary; check for macroprolactin |
| 100 – 200 | Marked elevation | Almost always prolactinoma; MRI required |
| > 200 | Severe high level of prolactin hormone | Almost diagnostic of macroprolactinoma (>1 cm) |
| > 500 | Very severe | Giant prolactinoma (rare) |
Confirmatory Tests
If initial prolactin levels are elevated, your doctor may order:
| Test | Purpose |
|---|---|
| Macroprolactin screen (PEG precipitation) | Distinguishes true elevated prolactin from benign macroprolactinemia |
| TSH (thyroid function) | Rules out hypothyroidism (reversible cause) |
| Pregnancy test (in women of childbearing age) | Pregnancy is a common physiological cause |
| Basic metabolic panel (BMP) | Screens for kidney and liver disease |
| MRI brain (pituitary protocol) | Detects prolactinoma or other pituitary masses |
| Visual field testing | If macroadenoma is found, assesses optic chiasm compression |
Part 7: Conditions Associated with Prolactin and Other Hormones
The relationship between prolactin and other hormones is complex. Here are key interactions.
Prolactin and Thyroid Hormone
- Hypothyroidism causes elevated prolactin because high TRH stimulates both TSH and prolactin.
- Treating hypothyroidism with levothyroxine normalizes prolactin levels in most cases.
Prolactin and Estrogen
- Estrogen stimulates prolactin secretion and lactotroph cell growth.
- This is why prolactin levels are higher in women than men, and why oral contraceptives or pregnancy can cause mild elevated prolactin.
Prolactin and Dopamine
- Dopamine is the primary inhibitor of prolactin.
- Anything that blocks dopamine (medications, pituitary stalk compression) raises prolactin.
- Dopamine agonists (bromocriptine, cabergoline) are used to treat high prolactin levels.
Prolactin and Cortisol
- Stress raises both cortisol and prolactin.
- Some pituitary tumors co-secrete prolactin and ACTH (causing Cushing’s disease).
Prolactin and Growth Hormone
- Some pituitary tumors co-secrete prolactin and growth hormone, causing acromegaly plus hyperprolactinemia.
Part 8: Treatment of High Prolactin Levels
Treatment depends on the cause of elevated prolactin.
1. Treat the Underlying Cause (If Reversible)
| Cause | Treatment |
|---|---|
| Medication-induced | Switch to alternative drug (e.g., change risperidone to aripiprazole or quetiapine). Do NOT stop psychotropics without psychiatric supervision. |
| Hypothyroidism | Levothyroxine replacement (normalizes prolactin in 2-4 months) |
| Pregnancy | No treatment needed; resolves after delivery |
| Breastfeeding | No treatment; resolves with weaning |
| Chest wall irritation | Treat the underlying condition (shingles, trauma) |
| Kidney or liver disease | Manage the primary organ failure |
2. Dopamine Agonists (First-Line for Symptomatic Hyperprolactinemia)
Dopamine agonists mimic dopamine, suppressing prolactin secretion and shrinking prolactinomas.
| Drug | Starting Dose | Maintenance Dose | Advantages | Disadvantages |
|---|---|---|---|---|
| Cabergoline (Dostinex) | 0.25 mg twice weekly | 0.5 – 2 mg twice weekly | More effective, better tolerated, once/twice weekly dosing | More expensive; rare cardiac valve fibrosis (at high doses > 2 mg/week) |
| Bromocriptine (Parlodel) | 1.25 mg daily (with food) | 2.5 – 7.5 mg twice daily | Less expensive | Poorly tolerated (nausea, dizziness, orthostatic hypotension); requires daily dosing |
Success rates:
- Cabergoline normalizes prolactin levels in 80-90% of patients.
- Tumors shrink by >50% in 70-80% of macroprolactinomas.
- Treatment is typically lifelong, but some patients can discontinue after 2-3 years if prolactin remains normal.
3. Surgery (Transsphenoidal Resection)
Indicated for:
- Prolactinomas resistant to dopamine agonists
- Patients intolerant of medication side effects
- Apoplexy (sudden hemorrhage into pituitary tumor)
- Optic chiasm compression not responding rapidly to medical therapy
Surgery cures 70-80% of microprolactinomas but only 30-50% of macroprolactinomas.
4. Radiation Therapy
Reserved for:
- Large, aggressive prolactinomas failing surgery and medication
- Malignant prolactinoma (extremely rare)
Part 9: Monitoring Prolactin Levels During Treatment
Once treatment begins, prolactin blood tests are repeated regularly:
| Time Point | Purpose |
|---|---|
| Baseline | Document high prolactin levels before treatment |
| 1 month | Assess initial response to dopamine agonist |
| 3 months | Adjust dose if needed |
| 6 months | Confirm normalization; repeat MRI if tumor present |
| Every 6-12 months (stable) | Long-term monitoring |
| Annually | For patients on high-dose cabergoline (>2 mg/week), echocardiogram to screen for valve disease |
Part 10: Prolactin and Fertility – A Special Focus
High prolactin levels are a common cause of infertility in both women and men. The good news: hyperprolactinemic infertility is highly treatable.
In Women
- Elevated prolactin suppresses GnRH → low LH/FSH → anovulation.
- Restoring normal prolactin levels with cabergoline or bromocriptine restores ovulation in 85-90% of women.
- If pregnancy occurs, dopamine agonists are typically stopped (they are pregnancy category B, but generally avoided unless necessary).
- Prolactin levels rise normally during pregnancy; the prolactinoma may enlarge slightly (risk < 2% for microprolactinomas, 20-30% for macroprolactinomas).
In Men
- High prolactin levels suppress GnRH → low LH → low testosterone → low sperm count.
- Restoring normal prolactin with dopamine agonists normalizes testosterone and sperm parameters in 70-80% of men.
- If hypogonadism persists, testosterone replacement may be added (but only after prolactin is normalized).
Summary Table: Key Facts About Prolactin
| Question | Answer |
|---|---|
| What is prolactin? | A peptide hormone produced by the pituitary gland; primary role is stimulating milk production. |
| What are prolactin? | Three forms: monomeric (active), big, and macroprolactin (inactive). |
| Normal prolactin levels | Women: 4-23 ng/mL; Men: 3-15 ng/mL. |
| High prolactin levels (hyperprolactinemia) | Women > 25 ng/mL; Men > 15 ng/mL. |
| Most common cause of elevated prolactin | Medications (antipsychotics, antiemetics, opiates). |
| Most common pathological cause | Prolactinoma (pituitary tumor). |
| Symptoms in women | Galactorrhea, irregular periods, infertility, low libido. |
| Symptoms in men | Erectile dysfunction, low libido, infertility, rare galactorrhea. |
| Prolactin blood test preparation | Morning draw, no breast stimulation, rest before draw, list medications. |
| First-line treatment for symptomatic hyperprolactinemia | Dopamine agonists (cabergoline or bromocriptine). |
| Can high prolactin be cured? | Yes, if caused by reversible factors (medication, hypothyroidism). Prolactinomas require long-term management. |
Conclusion: When to See a Doctor
If you experience any of the following, ask your doctor for a prolactin blood test:
- Unexplained milky nipple discharge (especially if not pregnant or breastfeeding)
- Irregular or absent menstrual periods
- Infertility (trying for 12+ months without success)
- Low libido or erectile dysfunction
- New-onset headaches with visual changes
- Delayed puberty in an adolescent
Understanding what is prolactin and recognizing the signs of high prolactin levels can lead to a simple diagnosis and highly effective treatment. Most causes of elevated prolactin are benign and reversible. Do not suffer in silence—a simple blood test and, if needed, a tiny pill once or twice weekly can restore your health, fertility, and quality of life.
Disclaimer: This article is for informational and educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider for interpretation of prolactin levels and personalized treatment recommendations.
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