PRL and Increased circulating prolactin concentration: Unlike patients with prolactinomas (with levels of serum prolactin typically between 2000 and 5000 mIU/L for microprolactinoma, and >10,000 mIU/L for macroprolactinoma) [53], patients with hyperprolactinaemia secondary to drug therapy typically only have mild elevations of serum prolactin (usually, but not invariably, <2000 mIU/L).