In some people, high blood levels of prolactin can be traced to causes other than a prolactinoma. Other causes include:
- Prescription drugs: Prolactin secretion in the pituitary is normally suppressed by the brain chemical dopamine. Drugs that block the effects of dopamine at the pituitary or deplete dopamine stores in the brain may cause the pituitary to secrete prolactin. These drugs include the major tranquilizers trifluoperazine (Stelazine) and haloperidol (Haldol); metoclopramide (Reglan) used to treat gastroesophageal reflux and the nausea caused by certain cancer drugs; and less often, alpha methyldopa and reserpine (Harmonyl) used to control hypertension.
- Other pituitary tumors: Other tumors may block the flow of dopamine from the brain, which normally inhibits its prolactin-secreting cells. Such so-called "mixed" tumors arise in or near the pituitary, and include those that release excessive growth hormone (acromegaly) or stimulate cortisol production (Cushing's syndrome). These can also cause the pituitary to secrete more prolactin.
- Some nonpituitary tumors: Prolactin secretion can also be caused by certain cancers, such as lung cancer.
- Hypothyroidism: Increased prolactin levels are often seen in people with hypothyroidism, and doctors routinely test people with hyperprolactinemia for hypothyroidism.
- Breast stimulation can modestly increase the amount of prolactin in the blood.
- Chest wall trauma (for example, an injury from a car steering wheel after an accident) can lead to increased levels of prolactin.
- Marijuana use is also a well documented cause of elevated levels of prolactin.
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