context: The pituitary gland is a pea-sized gland at the base of your brain. It makes several different hormones, including one called prolactin. Prolactin affects the mammary glands and helps women make breast milk. Sometimes, a tumor grows on the pituitary gland and makes too much prolactin. This kind of tumor is called a prolactinoma. It's the most common type of pituitary tumor and is most often benign, which means it's not cancer. A new mom's prolactin levels go up every time her baby nurses. But for men or women who aren't nursing, high prolactin in the blood can be a sign of a prolactinoma. Doctors don't know what causes it, but it's fairly common. It happens more often in women than men, and it's rare in kids. The signs of a prolactinoma are different in men and women. For women, typical symptoms of a small tumor include: Irregular menstrual periods Lack of menstrual periods Low sex drive Painful intercourse (caused by vaginal dryness) Problems with fertility Unusual production of breast milk Because changes in a woman's period are obvious, prolactinomas are more likely to be found early in premenopausal women. Postmenopausal women, who no longer get their periods, may not notice symptoms when the tumor is small. When a prolactinoma becomes large, it may press up against other nearby tissues. Symptoms then can include vision loss, vision changes, and headaches. When a man is diagnosed with a prolactinoma, it tends to be large. Men often aren't diagnosed when they have early signs, which include: Problems getting or maintaining an erection Decreased interest in sex Breast milk production in rare cases Headaches or vision problems are usually the symptoms that bring men to the doctor. You can expect a physical exam, a medical history questionnaire, and a blood test. If the test shows a high prolactin level, your blood also may be tested to find out how well your thyroid is working. If your doctor thinks you might have a pituitary tumor, he may order an MRI (magnetic resonance imaging). This uses powerful magnets and radio waves to get a clear picture of your pituitary gland. If a prolactinoma is found, you may need more blood tests to see if your pituitary gland is making other hormones like it should. You may also need more MRIs to see if the tumor grows and if it responds to treatment. Certain drugs can shrink it, especially when it's small. This works well for about 80% of people who have the tumor. The two approved medications for prolactinoma are bromocriptine ( Parlodel) and cabergoline ( Dostinex). They are dopamine agonists. These drugs act like the brain chemical dopamine, which normally keeps the pituitary gland from making too much prolactin. When medical treatment works, most premenopausal women get their periods again and regain their fertility. If medication doesn't shrink the tumor, or you can't take it because of side effects (like nausea or dizziness), your doctor may recommend surgery to take the tumor out through your nasal cavity. This returns prolactin levels to normal for about 80% of people with small tumors. But it's successful for only 30% to 40% of people with larger tumors. In rare cases, radiation therapy is used if medicine and surgery don't bring down prolactin levels. This works for about 1 in 3 people.