Low prolactin means your pituitary gland is producing less prolactin than your body needs. Normal prolactin levels range from 3 to 13 ng/mL in men and 3 to 27 ng/mL in women, though newer diagnostic research suggests levels below 5 ng/mL in men and below 7 ng/mL in women may signal a genuine deficiency. Low prolactin is uncommon compared to high prolactin, but it can affect breastfeeding, sexual function, and serve as an early warning sign of pituitary gland problems.
What Prolactin Does Beyond Breastfeeding
Most people associate prolactin with milk production, and that is its most well-known role. The pituitary gland, a pea-sized structure at the base of the brain, releases prolactin in increasing amounts during pregnancy to prepare the body for breastfeeding. After delivery, prolactin stays elevated to maintain milk supply as long as a mother continues nursing.
But prolactin also plays roles in sexual function, metabolic regulation, and reproductive health in both men and women. The hormone influences erection quality and ejaculatory function in men, and it contributes to normal ovarian cycling in women. This is why low prolactin can cause symptoms well beyond breastfeeding difficulty.
Symptoms in Women
For most women, the only noticeable symptom of low prolactin is an inability to produce enough breast milk after giving birth. This can range from a reduced supply to producing no milk at all, a condition called agalactia. Because breastfeeding problems are common and have many causes, low prolactin often goes unrecognized. Women who struggle to breastfeed are rarely tested for prolactin deficiency, which means the underlying problem can be missed for years.
In some cases, low prolactin may accompany broader hormonal imbalances that affect menstrual cycles or fertility, particularly when the pituitary gland itself is damaged. But isolated low prolactin in women tends to cause few symptoms outside of breastfeeding.
Symptoms in Men
In men, low prolactin appears to have a more noticeable impact on sexual health than previously recognized. Research on large cohorts of men seeking care for sexual dysfunction has found that those in the lowest prolactin range are more likely to experience erectile difficulties, particularly the type driven by psychological and neurological factors rather than blood flow problems alone. Men with moderate to severe erectile dysfunction tend to have lower prolactin levels than men with milder forms, even after accounting for age, weight, testosterone levels, and lifestyle factors like smoking and drinking.
Ejaculatory function is also affected. Men with very low prolactin report a reduced ability to control ejaculation and tend to have lower ejaculate volume. Studies using ultrasound imaging have found that these men have smaller seminal vesicles, the glands that produce much of the fluid in semen. The relationship between prolactin and ejaculate volume has been confirmed in studies of men being evaluated for couple infertility, though sperm quality itself doesn’t appear to be directly affected by prolactin levels.
What Causes Low Prolactin
The most common reason for low prolactin is medication. Drugs called dopamine agonists, specifically cabergoline and bromocriptine, are prescribed to treat prolactin-producing pituitary tumors. They work by binding to dopamine receptors on prolactin-producing cells in the pituitary, which shuts down prolactin release. Cabergoline is the stronger of the two and is used more frequently today. When these medications push prolactin levels too low, the symptoms described above can develop.
Physical damage to the pituitary gland is another cause. Head injuries, brain surgery, and radiation therapy to the head or neck can all impair the gland’s ability to produce prolactin along with other hormones. When the pituitary underperforms across the board, the condition is called hypopituitarism, and low prolactin is just one piece of a larger hormonal picture.
In women, one specific cause worth knowing about is Sheehan syndrome, which happens when severe bleeding during or after childbirth damages the pituitary gland. It accounts for 6 to 8% of all cases of hypopituitarism. The hallmark presentation is a woman who experiences heavy postpartum bleeding, then cannot breastfeed, and later notices her periods don’t return. A prolactin level checked in the postpartum period can be the first clue that something is wrong. Depending on the population studied, Sheehan syndrome has been found in up to 3.1% of women who have given birth, though in countries with better obstetric care the prevalence drops significantly.
How Low Prolactin Is Diagnosed
Diagnosis starts with a simple blood test. Because prolactin fluctuates throughout the day and can spike from stress, eating, or exercise, samples are typically drawn in the morning after fasting. A single low reading doesn’t always mean there’s a problem. Diagnostic research suggests that a baseline level at or below 5.7 ng/mL in men and 7.1 ng/mL in women predicts a genuine prolactin deficiency with high specificity.
If your baseline level is borderline, your doctor may order a stimulation test. This involves injecting a substance called TRH (thyrotropin-releasing hormone), which normally triggers the pituitary to release a burst of prolactin. A healthy response means prolactin rises to at least 18 ng/mL in men or 41 ng/mL in women. A blunted response confirms that the pituitary’s prolactin-producing cells aren’t working properly.
When low prolactin is confirmed, imaging of the pituitary with an MRI is often the next step, particularly if there’s suspicion of a tumor, prior head injury, or a condition like Sheehan syndrome where the pituitary may appear partially or completely empty on imaging.
Treatment Approaches
There is no prolactin replacement therapy the way there is for thyroid hormone or cortisol. Instead, treatment focuses on identifying and addressing whatever is causing the deficiency. If a dopamine agonist medication has suppressed prolactin too aggressively, your doctor may lower the dose or switch to a different drug. When a pituitary tumor or structural damage is involved, treating the underlying condition can sometimes restore normal hormone production.
For women trying to breastfeed, the practical reality is that if prolactin levels can’t be raised sufficiently, supplemental feeding may be necessary. For men experiencing sexual symptoms linked to low prolactin, the picture is still evolving clinically. Because low prolactin in men often coexists with other hormonal changes, treatment usually involves a broader evaluation of pituitary function rather than targeting prolactin alone.
Does Low Prolactin Weaken Your Immune System?
Early animal studies raised concerns that prolactin deficiency might impair immune function, since rats with their pituitary glands removed showed thymus shrinkage and lower white blood cell counts. But more rigorous research using mice specifically bred without prolactin receptors found no meaningful immune deficits. These mice had normal immune cell populations in their bone marrow, thymus, spleen, and lymph nodes. Their immune cells responded normally to stimulation, generated normal antibody levels after vaccination, rejected foreign tumor cells, and fought off bacterial infections just as effectively as normal mice. The current evidence suggests that prolactin is not essential for immune function, so low prolactin alone is unlikely to make you more vulnerable to infections.