What are the functions of prolactin? Prolactin is a hormone that is well known for its role in breast milk production. Women experience large spikes in prolactin levels during pregnancy, especially in the third trimester, which stimulates the growth and development of mammary tissue in preparation for milk production. Although this is the primary function of this hormone, it also contributes to hundreds of other physiological processes. Men generally have lower serum prolactin concentrations than women. As a result, the number of other roles that this hormone plays, especially in men, are usually overlooked. In fact, as well as milk production, prolactin is responsible for regulating the immune system, metabolism and reproductive systems in both sexes. Therefore, when the hormone levels in the blood begin to fluctuate, it causes some disorders in the body. There are many potential causes of elevated blood prolactin levels (hyperprolactinemia) in men, such as medications, an underactive thyroid gland, or a prolactinoma, a benign tumor of the pituitary gland. What are the effects of high prolactin in men? Complaints vary from case to case, and there are not always signs when elevated prolactin levels are caused by a prolactinoma. However, if the tumor puts pressure on surrounding tissue, it can cause problems. Because of the important role prolactin plays in the reproductive system, symptoms in men usually include: Erectile dysfunction; Reduced body and facial hair; Low bone density; Decreased libido; Decreased testosterone production; Infertility. The most reliable way to check prolactin levels is through a blood test. What causes high serum prolactin levels in men? Prolactinoma is the most common tumor of the pituitary gland, accounting for about 40% of all pituitary tumors. This benign tumor can cause the pituitary gland to produce too much of the hormone prolactin (hyperprolactinemia), leading to low testosterone levels in men. Unfortunately, the cause of these tumors is not fully understood and they are less common in men. Hyperprolactinemia induces hypogonadism by inhibiting (suppressing) the pulsatile secretion (secretion in a correct time pattern) of gonadotropin-releasing hormone, and therefore follicle-stimulating hormone, luteinizing hormone, and testosterone. This leads to cessation of spermatogenesis, impaired sperm motility and quality, and results in testicular morphological changes similar to those seen in prepubertal testes. According to their size, tumors (pituitary adenomas) are divided into microadenomas (under 10 mm) and macroadenomas (over 10 mm). Men with hyperprolactinaemia present more often with macroadenoma than with microadenoma. Symptoms directly related to hypogonadism predominate.In men, hypogonadism leads to impaired libido, erectile dysfunction, reduced ejaculate volume and oligospermia. Other potential causes of elevated prolactin levels include: Medications Taking a medication that affects dopamine production may also have an effect on prolactin production. This means that medications used to treat mental illness, high blood pressure (hypertension) and pain relievers may affect prolactin levels. Other conditions In addition to reduced thyroid function (hypothyroidism), kidney disorders and herpes zoster can affect prolactin levels. References: 1. Mayo Clinic. Prolactinoma 2. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Prolactinoma 3. PubMed. Hyperprolactinemia in men: clinical and biochemical features and response to treatment