The mesylate salt of bromocriptine, a semisynthetic ergot alkaloid with dopaminergic, antidyskinetic, and antiprolactinemic activities. Bromocriptine selectively binds to and activates postsynaptic dopamine D2 receptors in the corpus striatum of the central nervous system (CNS). Activation of these D2 receptors activate inhibitory G-proteins, which inhibit adenylyl cyclase, preventing signal transduction mediated via cAMP and resulting in the inhibition of neurotransmission and an antidyskinetic effect. Ths agent also stimulates dopamine D2 receptors in the anterior pituitary gland, which results in the inhibition of prolactin secretion and lactation and may inhibit the proliferation of prolactin-dependent breast cancer cells.