Causes of High Prolactin Levels
Other tumors arising in or near the pituitary -- such as those that cause acromegaly or Cushing's syndrome -- may block the flow of dopamine from the brain to the prolactin-secreting cells.
Another cause of high prolactin levels is hypothyroidism. Increased prolactin levels are often seen in people with hypothyroidism, and doctors routinely test people with hyperprolactinemia for hypothyroidism.
Breast stimulation also can cause a modest increase in the amount of prolactin in the blood.