The active ingredient in Bromocriptine, bromocriptine mesylate, acts by stimulating dopamine D2 receptors, which has multiple physiological effects. For patients with Parkinson’s disease, this stimulation helps counter the dopamine deficiency typically seen in the disease, leading to improvement in symptoms such as rigidity, tremors, and bradykinesia. In conditions related to high levels of prolactin (like prolactinomas and certain fertility issues), Bromocriptine’s effect on dopamine receptors leads to decreased secretion of prolactin from the pituitary gland, often resulting in normalization of prolactin levels, shrinkage of prolactinoma tumors, and restoration of fertility in some cases.