MSH: A dopamine D2 antagonist that is used as an antiemetic.,NCI: A drug that increases the motility (movements and contractions) of the stomach and upper intestine. It is used to treat certain stomach problems and nausea and vomiting caused by chemotherapy. It is a type of antiemetic and a type of motility agent.,NCI: A substituted benzamide and a derivative of para-aminobenzoic acid (PABA) that is structurally related to procainamide, with gastroprokinetic and antiemetic effects. Metoclopramide exerts its prokinetic effect by antagonizing dopamine mediated relaxation effect on gastrointestinal smooth muscle. This enhances the response of the gastrointestinal smooth muscle to cholinergic stimulation, thereby leading to an increase of gastric emptying into the intestines. Metoclopramide may also strengthen the lower esophagus sphincter, thereby preventing acid reflux. This agent antagonizes D2 dopamine receptors in chemoreceptive trigger zone (CTZ) of the medulla, thereby preventing nausea and vomiting.