Nipple discharge, known as galactorrhea, is the production of milk-like fluid from the breast that is not associated with pregnancy or breastfeeding. This side effect can occur in both women and men and is a relatively common occurrence following the initiation of certain prescription drugs. While the discharge is usually benign and not a sign of a serious underlying condition, it is understandably a source of concern for patients. Numerous medications can inadvertently disrupt the body’s hormonal balance, leading to this fluid production.
Understanding the Prolactin Connection
The production of breast milk is regulated by the pituitary hormone prolactin, and medications that cause discharge primarily do so by elevating this hormone’s level. The pituitary gland is constantly under the inhibitory influence of the neurotransmitter dopamine, which acts as the main prolactin-inhibiting factor. Dopamine released from the hypothalamus binds to D2 receptors on the pituitary cells, effectively suppressing prolactin secretion.
When a medication blocks these D2 receptors or interferes with dopamine signaling, the inhibitory brake on the pituitary is released. This results in hyperprolactinemia, an excess of prolactin in the bloodstream, subsequently triggering milk production. Drug-induced galactorrhea is typically milky in appearance and often affects both nipples (bilateral discharge). This presentation is often reassuring, as unilateral, bloody, or clear discharge suggests a different, more localized cause that requires immediate investigation.
Drug Classes That Elevate Prolactin
The largest category of medications known to induce galactorrhea includes those that act directly on dopamine receptors. Antipsychotic drugs are the most frequent culprits, particularly conventional or first-generation agents, as well as some second-generation antipsychotics like risperidone and amisulpride. These drugs block dopamine receptors to treat conditions like psychosis, which inadvertently blocks D2 receptors in the prolactin-regulating pathway. Prolactin levels can rise significantly, sometimes exceeding ten times the normal pre-treatment values.
Certain antidepressants also carry a risk, though the mechanism is less direct than with antipsychotics. Selective Serotonin Reuptake Inhibitors (SSRIs) and Tricyclic Antidepressants (TCAs) can cause hyperprolactinemia by increasing serotonin activity. Serotonin stimulates prolactin release and can indirectly reduce dopamine activity, disinhibiting prolactin secretion. Opioid medications, often used for chronic pain management, can also elevate prolactin levels by decreasing dopamine release from the hypothalamus.
Other medication classes affect prolactin through different pathways, including agents used for gastrointestinal and cardiovascular conditions. Drugs that enhance gut motility, such as metoclopramide and domperidone, are potent D2 receptor blockers known to cause hyperprolactinemia. Certain antihypertensive drugs, like the calcium channel blocker verapamil and older agents such as methyldopa, can also increase prolactin by interfering with hypothalamic dopamine production. High-dose estrogen therapies, including some hormonal birth control methods, can stimulate the pituitary cells to produce more prolactin, leading to discharge.
When to Consult a Healthcare Provider
Experiencing unexpected nipple discharge should prompt a discussion with a healthcare provider to determine the precise cause. A prescribed medication must never be stopped abruptly without first consulting the physician who prescribed it. Discontinuing treatment suddenly can lead to a return of the underlying medical condition or cause severe withdrawal symptoms.
The provider will begin with a physical examination, noting the color and nature of the discharge, and will likely order a series of tests. Blood work is standard and includes checking serum prolactin levels to confirm hyperprolactinemia, and a pregnancy test to rule out the most common physiological cause. Thyroid-stimulating hormone (TSH) levels may also be checked, as an underactive thyroid can indirectly lead to elevated prolactin.
If the prolactin levels are significantly elevated, or if the discharge is unilateral or bloody, imaging tests may be necessary. A mammogram or breast ultrasound can rule out localized breast pathology, while an MRI of the brain may be performed to exclude a pituitary tumor, which is another cause of high prolactin. Management options depend on the severity of the symptoms and the specific medication involved, and may include adjusting the dose, switching to an alternative drug with a lower risk of prolactin elevation, or adding a short course of a dopamine agonist medication.