Prolactin is a hormone primarily recognized for its role in enabling milk production in females. It is present in both men and women, though typically at lower levels in non-pregnant individuals. When prolactin levels become abnormally high, a condition known as hyperprolactinemia occurs. While various physiological and pathological factors can lead to this elevation, medications are a common and sometimes overlooked cause.
Mechanisms of Prolactin Elevation
The body tightly regulates prolactin secretion from the pituitary gland, a small gland located at the base of the brain. A key regulator is dopamine, a neurotransmitter that acts as a continuous inhibitory signal, essentially a “brake,” on prolactin release from specialized cells called lactotrophs in the pituitary. This inhibitory control is a unique aspect of prolactin regulation compared to other pituitary hormones.
Medications can disrupt this delicate balance primarily by interfering with dopamine’s action. Many drugs increase prolactin by blocking dopamine D2 receptors, particularly those located on the pituitary lactotrophs. When these receptors are blocked, dopamine cannot exert its inhibitory effect, leading to an uncontrolled increase in prolactin secretion. Other medications may deplete dopamine levels or enhance other pathways that stimulate prolactin release, thereby removing the “brake” and allowing prolactin levels to rise.
Common Medication Classes
Numerous medication classes can cause elevated prolactin levels, primarily by affecting dopamine pathways. The degree of elevation and the likelihood of this side effect vary significantly between different drugs and patient populations.
Antipsychotics are a major group of medications known to increase prolactin. First-generation antipsychotics like haloperidol and chlorpromazine, and some second-generation ones such as risperidone and paliperidone, are particularly prone to causing significant and sustained elevations due to their strong dopamine D2 receptor blockade. Other atypical antipsychotics, including olanzapine, quetiapine, and clozapine, generally have a lower or transient impact on prolactin levels.
Antidepressants can also contribute to increased prolactin, though typically to a lesser extent than many antipsychotics. Selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs) have been implicated, potentially through their effects on serotonergic pathways that can indirectly influence dopamine.
Antiemetics, commonly used to treat nausea and vomiting, often elevate prolactin due to their potent dopamine D2 receptor blocking action. Metoclopramide and domperidone are prominent examples in this category. These drugs block dopamine receptors in the chemoreceptor trigger zone, which also affects the pituitary’s prolactin regulation.
Certain antihypertensives, such as methyldopa and verapamil, can also lead to higher prolactin levels. Methyldopa can deplete dopamine, while verapamil may reduce central dopamine production by affecting calcium channels.
Opioids have been shown to stimulate prolactin secretion, primarily by inhibiting dopamine release in the hypothalamus. This effect is mediated through various opioid receptors. Histamine H2-receptor antagonists like cimetidine and ranitidine, used for acid reduction, have also been reported to increase prolactin, although ranitidine’s effect appears less consistent than cimetidine’s. Proton pump inhibitors (PPIs) such as omeprazole and lansoprazole have also been linked to potential prolactin elevation, though the exact mechanisms are still being explored.
Managing Medication-Induced High Prolactin
If there is a suspicion that a medication is causing elevated prolactin levels, it is important to consult a healthcare provider. Symptoms of high prolactin can include irregular or absent menstrual periods, unexpected breast milk production (galactorrhea), infertility, decreased libido, and in men, erectile dysfunction or breast enlargement.
A doctor can confirm elevated prolactin through a simple blood test. It is crucial for individuals to never stop or alter their prescribed medication without medical guidance. Healthcare providers will assess the risk-benefit profile of the medication causing the elevation. Management strategies may involve adjusting the dose of the current medication, switching to an alternative drug with a lower propensity to increase prolactin, or, in some cases, adding another medication to counteract the prolactin-raising effect. The goal is to manage symptoms and restore prolactin levels to a healthy range while maintaining the effectiveness of the necessary treatment.