Pituitary adenomas are most commonest cause of pituitary hormone hypersecretion and hyposecretion syndromes, common in adults. Hyperprolactinemia is the most common pituitary hormone hypersecretion syndrome in both men and women. PRL-secreting pituitary adenomas (prolactinomas) are the most common cause of PRL levels >200microgram/L. Pituitary adenomas are a result of excessive secretion of prolactin, inhibiting hypothalamic release of LHRH resulting in defective LH and FSH secretion. This defective LH and FSH secretion results in decreased levels of estrogen in females and testosterone in males. This is a reason how excessive prolactin can cause hypogonadism. In men with hyperprolactinemia, diminished libido, infeility, and visual loss (from optic nerve compression) are the usual presenting symptoms. Amenorrhea, galactorrhea, and infeility are the hallmarks of hyperprolactinemia in women. If hyperprolactinemia develops before menarche, primary amenorrhea results. Basal, fasting morning PRL levels (normally <20micrograms/L) should be measured to assess hypersecretion.the diagnosis of prolactinoma is likely with a PRL level >200 micrograms/L. PRL levels <100micrograms/L may be caused by microadenomas. MRI should be performed in all patients with hyperprolactinemia. Dopamine agonists are effective for most causes of hyperprolactinemia. An ergoline derivative, cabergoline is a long-acting dopamine agonist with high D2 receptor affinity. The drug effectively suppresses PRL for >14 days after a single oral dose and induces prolactinoma shrinkage in most patients. The ergot alkaloid bromocriptine mesylate is a dopamine receptor agonist that suppresses prolactin secretion. Indications for surgical adenoma debulking include dopamine resistance or intolerance and the presence of an invasive macroadenoma with compromised vision that fails to improve after drug treatment. Ref: Harrison's Internal Medicine, 18th Edition, Pages 2880, 2887-2890, 3051, 3389, 2897-2899