Aprepitant is a medication used to prevent nausea and vomiting caused by chemotherapy or surgery. It belongs to a class of drugs known as neurokinin-1 (NK-1) receptor antagonists.

Chemotherapy and certain surgical procedures can trigger the release of a substance called substance P, which stimulates the vomiting center in the brain, leading to nausea and vomiting. Aprepitant works by blocking the action of substance P at NK-1 receptors in the brain, thereby reducing the likelihood of nausea and vomiting.