An anti-emetic is a drug that is effective against vomiting and nausea. Anti-emetics are typically used to treat motion sickness and the side effects of opioid analgesics, general anaesthetics and chemotherapy directed against cancer.
Types of Anti-emetics
- 5-HT3 receptor antagonists - these block serotonin receptors in the central nervous system and gastrointestinal tract. As such, they can be used to treat post-operative and cytotoxic drug nausea & vomiting.
- Dopamine antagonists act in the brain and are used to treat nausea and vomiting associated with neoplastic disease, radiation sickness, opioids, cytotoxic drugs and general anaesthetics.
- Droperidol, Haloperidol, Chlorpromazine, Promethazine, Prochlorperazine. Some of these drugs are limited in their usefullness by their extra-pyramidal and sedative side-effects.
- Metoclopramide also acts on the GI tract as a pro-kinetic, and is thus useful in gastrointestinal disease; however, it is poor in cytotoxic or post-op vomiting.
- Antihistamines (H1 histamine receptor antagonists), effective in many conditions, including motion sickness and severe morning sickness in pregnancy.
- Cannabinoids are used in patients with cachexia, cytotoxic nausea & vomiting or are unresponsive to other agents.
- Cannabis (Marijuana). Most patients prefer smoked or vaporized cannabis over pharmaceutical versions because they do not contain all 66 cannabinoids that are in cannabis, many of which have medicinal applications. CBD is a main cannabinoid not in Marinol or Cesamet.
- Dronabinol (Marinol). Ninety percent of sales are for cancer and AIDS patients. The other 10% of its sales thought to be for pain, Multiple Sclerosis and also for Alzheimer's disease.
- Nabilone (Cesamet). Put back on the market in late 2006. A Schedule II substance unlike Marinol which is Schedule III and cannabis which is Schedule I.
- Sativex is an oral spray containing THC and CBD. It is currently legal in Canada and a few countries in Europe but not in the U.S. yet.
- Midazolam given at the onset of anaesthesia has been shown in recent trials to be as effective as ondansetron, a 5HT3 antagonist in the prevention of post-operative nausea and vomiting. Further studies need to be undertaken.
- Lorazepam said to be very good as an adjunct treatment for nausea along with first line medications such as Compazine or Zofran.
- Dexamethasone given in low dose at the onset of a general anaesthetic for surgery is an effective anti-emetic. The specific mechanism of action is not fully understood.
- Trimethobenzamide; thought to work on the CTZ
- Emetrol also claimed to be an effective anti-emetic.
- Propofol given intravenously. It has been used in an acute care setting in hospital as a rescue therapy for emesis.
- Peppermint claimed to help nausea or stomach pain when added into a tea or peppermint candies.
- Muscimol purported as such 
- Non-pharmaceutical therapies with some evidence of efficacy include acupuncture and hypnosis. All drugs have potential side effects. It is important to try to reduce the baseline risk of nausea and vomiting, particularly with respect to surgery.