What Are They, How Do They Work, What Are They Used For, and More

Author: Lahav Constantini

Editors: Antonella Melani, MD, Nimmit Vyas, PharmD

Illustrator: Jillian Dunbar

What are antiemetic drugs?

Antiemetic drugs are medications used to treat nausea and vomiting. These two symptoms are very common and can be caused by many different conditions, therapies, procedures, and medications (such as opioids). Though vomiting is considered to be a protective reflex of the body to expel toxic substances in the stomach and gut, antiemetic drugs are often necessary to suppress vomiting, especially if there’s severe dehydration.

What does antiemetic mean?

Antiemetic literally means ‘against emesis’, otherwise known as against vomiting.

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How do antiemetics work?

Antiemetics work on the neural pathways involved with vomiting by blocking specific receptors that respond to neurotransmitter molecules, such as serotonin, dopamine, and histamine. Most of these are central receptors found in the vomiting center of the brainstem, while peripheral receptors are found in the vagus nerve. When the gastrointestinal tract senses a threat, it sends information to the peripheral receptors, which in turn convey the information to the central receptors in the vomiting center. In response, the vomiting center triggers nausea and vomiting by stimulating the gastrointestinal tract, abdominal muscles, and the diaphragm.

What are the side effects of antiemetic drugs?

Antiemetics are generally well-tolerated, but can have potential side effects, such as constipation or diarrhea, headache, fatigue, malaise, dizziness, light-headedness, blurred vision, dry mouth, or photosensitivity. Consulting the family physician before taking over the counter antiemetics or prescription drugs is vital, especially if taking any other medications at the same time due to potential additive effects. 

What are antiemetic drugs used for?

Antiemetic drugs are taken to treat nausea and vomiting, and can be administered as tablets, sublinguals, oral solutions, suppositories, transdermal patches or intravenous injections. Nausea and vomiting can be symptoms of various conditions, such as motion sickness, upper abdominal irritation, food poisoning, and gastroenteritis. Nausea and vomiting are also common side effects of many drugs including opioid analgesics, anaesthetics (postoperative nausea), and chemotherapy directed against cancer. Finally, nausea and vomiting are often experienced in pregnancy-related morning sickness or hyperemesis gravidarum, which is extreme morning sickness including severe vomiting, during pregnancy. However, antiemetic medications should not be taken during pregnancy without first consulting with your family physician, who might prescribe them only after weighing the risks and benefits. 

What are some examples of antiemetics?

There are a few classes of antiemetic medications, which are categorized based on the predominant receptor they act on. Choosing the most appropriate one is key in order to optimize effectiveness and minimize side effects. 

5-HT3 receptor antagonists, such as ondansetron (Zofran), granisetron, and palonosetron (2nd generation) are medications that work on central serotonin receptors in the vomiting center, as well as the peripheral serotonin receptors in the vagus nerve. 5-HT3 receptor antagonists are indicated for use against vomiting caused by acute gastroenteritis or postoperative nausea. It’s also the first go-to antiemetic class for radiotherapy- and chemotherapy-induced nausea and vomiting, which are common side effects. 

Dopamine antagonists, such as metoclopramide (Reglan), domperidone (Motilium), and chlorpromazine, are amongst the most commonly used antiemetics, and they’re also indicated for postoperative nausea and motion sickness. 

H1 antihistamines, such as cyclizine, promethazine, and diphenhydramine, or antimuscarinics (anticholinergics) like scopolamine (Hyoscine) are often used to treat and prevent nausea and vomiting induced by vestibular disturbances like vertigo or motion. Scopolamine is predominantly used to prevent motion sickness, and can come in a transdermal patch, making it easier to administer, especially for people with swallowing problems. The transdermal patch is also useful for maintaining a steady release of the medication and lowering the risk of side effects. As a downside, antihistamines generally lead to drowsiness.

Glucocorticoids are also indicated as antiemetics against chemotherapy-induced emesis. They are effective and generally well-tolerated, but insomnia, increased energy, and mood changes are common side effects.

Neurokinin 1 (NK-1) receptor antagonists, like aprepitant (Emend) and rolapitant (Varubi), are a relatively new medication class that can be used as antiemetics, especially for suppressing radiotherapy- and chemotherapy-induced nausea and vomiting, as well as to prevent nausea and vomiting after surgery. NK-1 receptor antagonists should not be taken while pregnant or breastfeeding.

What is the most effective antiemetic?

Out of all medications indicated for vomiting, it’s difficult to choose the most effective one. The medication should be appropriately chosen by a healthcare professional according to the situation and the person in need of it, as well as taking into consideration the underlying cause, the severity of the case, and the possible side effects.

Which antiemetic is indicated for use with vertigo?

Vertigo is an illusion of motion often accompanied by headaches, nausea, and vomiting. Most often, H1 receptor antagonists from the antihistamines class, like loratadine, can be prescribed. In any case, the appropriate medication for each person is chosen after careful assessment by a healthcare professional.

What are the most important facts to know about antiemetics?

Antiemetics are medications aimed at preventing or treating nausea and vomiting, which are common symptoms that may be tied to numerous different causes. For instance, motion sickness, gastroenteritis, and as a side effect of other treatments can all commonly lead to nausea. There are many classes of antiemetic medications, so they should be appropriately prescribed or recommended by a healthcare professional, taking into consideration the person in need of it, the underlying cause, the severity of the case, and the possible side effects. Possible side effects of antiemetic medications include headache, fatigue, dizziness, dry mouth, and abnormal defecation. Choosing the appropriate antiemetic medication should be carefully done by the family physician, taking into consideration the severity and cause of the symptoms, as well as any underlying diseases or medications taken by the person.

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Related links

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Clinical Reasoning: Pediatric vomiting
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Clinical Reasoning: Dizziness and vertigo

Resources for research and reference

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