Phenothiazine antiemetics 

Phenothiazine antiemetics are a type of medicine that may be used to relieve nausea and vomiting. They work by inhibiting dopamine, muscarinic and histamine (H1) receptors generally in the vomiting center and chemoreceptor trigger zone.

Phenothiazine antiemetics are usually reserved for severe cases of nausea and vomiting that occur as a result of chemotherapy or radiotherapy. Drowsiness and extrapyramidal side effects (unusual movement disorders) are common side effects. Some phenothiazine antiemetics are also used in the treatment of psychosis and schizophrenia.

Phenothiazines, including prochlorperazine, chlorpromazine, and promethazine, are commonly employed in the emergency department to treat severe nausea and vomiting accompanying migraine.

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.

Ondansetron and promethazine belong to different drug classes. Ondansetron is an anti-nausea medication and promethazine is a phenothiazine.