An antiemetic is a drug that is effective against vomiting and nausea. Antiemetics are typically used to treat motion sickness and the side effects of opioid analgesics, general anaesthetics, and chemotherapy directed against cancer. They may be used for severe cases of gastroenteritis, especially if the patient is dehydrated.

Some antiemetics previously thought to cause birth defects appear safe for use by pregnant women in the treatment of morning sickness and the more serious hyperemesis gravidarum.