What causes hyperprolactinemia?

Hyperprolactinemia is not always abnormal. High prolactin levels are expected during pregnancy and breastfeeding.

Certain medications, especially those used in psychiatric disorders, are expected to raise prolactin levels, although in some cases they may not cause symptoms of hyperprolactinemia. In those people who do experience symptoms, the treating doctor may decide to change the type of medication. Aripiprazole, a medication that is used to treat schizophrenia and bipolar mood disorder, is the best option in these cases.^[1] Additional medications may also be added to reduce the prolactin levels.

Hypothyroidism can also cause hyperprolactinemia, and a thyroid function test should be included as part of the work up when assessing a high prolactin level. Other disorders of the pituitary gland, such as Cushing’s disease, might raise prolactin, as might chronic kidney and liver disorders.^[2]

In some cases, the cause is never found. This is referred to as idiopathic hyperprolactinemia.^[3] Sometimes this diagnosis can be explained by macroprolactin, a type of prolactin molecule that is larger and bound to immunoglobulins. It does not bind as easily to prolactin receptors in the body as prolactin does, so it usually will not cause the common symptoms of hyperprolactinemia, but testing will still show a high prolactin level when macroprolactin is elevated. Asymptomatic hyperprolactinemia caused by macroprolactin does not require treatment. Testing for this molecule is possible but it is difficult and expensive and so is not always an option.^[4][5]