According to the National GI Survey published in 2018, which polled over 71,000 Americans, nausea is a highly prevalent gastrointestinal symptom, affecting nearly 10% of individuals. However, various medications are available that may help manage these symptoms effectively.
Over-the-counter and prescription antiemetics are medications designed to prevent or alleviate nausea and vomiting, which can significantly impact the quality of life regardless of the underlying cause.
This guide explores the various types of antiemetics, their potential uses, and associated side effects, providing a clear understanding of how these medications can help manage these bothersome symptoms in different scenarios.
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What Are Antiemetics?
Antiemetics is a class of medications used to prevent and treat nausea and vomiting.
Nausea and vomiting can result from various causes, such as:
- Gastroparesis (the slowed movement of food from the stomach into the small intestine)
- Gastroenteritis (gastrointestinal infection)
- Pregnancy
- Motion sickness
- Vertigo
- Migraine headaches
- Medication side effects
How Antiemetics Work
The nausea and vomiting reflex is a protective mechanism triggered by the brain's vomiting center, located in the medulla oblongata. This center integrates signals from several pathways that detect harmful or disruptive stimuli, initiating a coordinated physiological response to expel potentially harmful substances from the stomach.
Three primary pathways can activate the vomiting center:
- Vestibular Fibers: Associated with the inner ear and balance
- Afferent Visceral Fibers: Nerves that carry signals from the stomach, intestines, and other abdominal organs to the brain
- Chemoreceptor Trigger Zone: This area of the brain is highly sensitive to circulating toxins, drugs, and metabolic changes
Chemical messengers called neurotransmitters, including histamine, dopamine, serotonin, acetylcholine, and neurokinin, facilitate the activation of the vomiting reflex through these various pathways. Antiemetic therapies aim to modulate these neurotransmitters, potentially reducing signals to the vomiting center.
Types of Antiemetics
Antiemetics can fit into various classes based on the vomiting pathways they target. Some medications target more than one pathway.
Antihistamines
Antihistamines block histamine (H1) receptors in the vestibular system and vomiting center, reducing signals related to motion sickness and inner ear disturbances.
Examples of antihistamine antiemetics include:
- Diphenhydramine
- Dimenhydrinate
- Meclizine
- Promethazine
Anticholinergics
Anticholinergics work by blocking muscarinic acetylcholine receptors, which are part of the communication system between the inner ear (the vestibular system) and the brain's vomiting center. The vestibular system helps with balance and spatial orientation, but when disturbed, it sends signals to the vomiting center that can cause nausea and vomiting.
Many H1 blockers, such as diphenhydramine and meclizine, also have anticholinergic properties that contribute to their antiemetic effects.
Examples of anticholinergic antiemetics include:
- Diphenhydramine
- Meclizine
- Scopolamine
- Dimenhydrinate
Dopamine Antagonists
Dopamine antagonists block dopamine (D2) receptors in the chemoreceptor trigger zone and intestines to suppress nausea and vomiting. These medications also block serotonin, histamine, and muscarinic receptors at higher doses.
Examples of dopamine antagonist antiemetics include:
- Metoclopramide
- Promethazine
- Prochlorperazine
Serotonin Antagonists
Serotonin antagonists block serotonin (5-HT3) receptors in the chemoreceptor trigger zone and the gut. They have largely replaced dopamine antagonists in treating nausea and vomiting.
The U.S. Food and Drug Administration (FDA) approves the use of serotonin antagonists in children and adults to prevent nausea and vomiting related to chemotherapy, radiation therapy, and anesthesia.
Examples of serotonin antagonist antiemetics include:
- Ondansetron
- Granisetron
- Palonosetron
Neurokinin Antagonists
Neurokinin-1 (NK1) receptor antagonists are a class of medication that is FDA-approved for treating postsurgical and chemotherapy-induced nausea and vomiting (CINV). These medications block NK1 receptors, which are activated by a natural chemical called substance P. Substance P induces vomiting when it binds to these receptors.
Examples of neurokinin antagonists include:
- Aprepitant
- Fosaprepitant
Corticosteroids
Corticosteroids have been used since the 1980s to prevent CINV. While the precise mechanism of action remains unclear, it is speculated that corticosteroids inhibit prostaglandin production in the brain and gut, thereby reducing inflammation and contributing to their antiemetic effects. They are often combined with other antiemetics to augment their effects.
Examples of corticosteroids used to treat nausea and vomiting include:
- Methylprednisolone
- Dexamethasone
Benzodiazepines
While primarily approved for treating anxiety, benzodiazepines are sometimes used off-label to prevent and treat nausea and vomiting associated with chemotherapy and surgery. They enhance the effect of gamma-aminobutyric acid (GABA) in the brain.
Examples of benzodiazepines that are prescribed for nausea and vomiting include:
- Lorazepam
- Alprazolam
Cannabinoids
Cannabinoids are chemical compounds that can be produced naturally by the body (endocannabinoids), found in plants like cannabis (phytocannabinoids), or created synthetically in labs. These compounds bind cannabinoid (CB1) receptors in the nervous system to suppress signals that trigger nausea and vomiting.
The FDA approved two cannabinoid derivatives in 1985 for treating CINV:
- Dronabinol
- Nabilone
Complementary and Alternative Therapies
For those who prefer natural approaches or seek complementary therapies, evidence suggests that several options can help alleviate nausea:
Ginger
Historically, this herb has been used for centuries for nausea and vomiting. Clinical studies suggest ginger may help ameliorate nausea and vomiting caused by pregnancy, motion sickness, and chemotherapy, potentially through its ability to inhibit 5-HT3 receptors.
Peppermint Oil
Aromatherapy with peppermint essential oil may also be a safe and effective intervention for CINV. Researchers conducting a 2013 study concluded that Mentha spicata and Mentha × piperita essential oils reduced the number and intensity of emetic events within 24 hours of chemotherapy.
Vitamin B6
The American College of Obstetricians and Gynecologists (ACOG) recommends taking vitamin B6 (pyridoxine) with or without doxylamine to manage nausea and vomiting during pregnancy. A typical dose recommendation is 10-25 mg three to four times daily. Little research supports that vitamin B6 can help alleviate other types of nausea and vomiting.
Acupressure
A randomized control trial published in 2022 demonstrated that women with hyperemesis gravidarum who applied acupressure at the P6 point (on the inner side of the wrist) for at least 30 minutes daily experienced less severe nausea and vomiting. Another positive clinical outcome observed in this study was less frequent administration of antiemetic medication.
Uses of Antiemetics in Medical Conditions
Understanding the mechanisms of action for different classes of antiemetics helps healthcare providers select the most effective treatment for various clinical scenarios.
Antiemetics should be used under the guidance of a healthcare provider to ensure appropriate treatment.
Post-Surgical Nausea
Postoperative nausea and vomiting (PONV) is one of the most common complications following surgery, on average affecting 20-30% of patients. In high-risk patient populations, this rate increases to up to 80%. PONV can delay recovery, extend hospital stays, increase healthcare costs, and decrease patient satisfaction.
To manage PONV, healthcare providers often prescribe:
- Ondansetron (5-HT3 antagonist)
- Metoclopramide (dopamine antagonist)
- Dexamethasone (corticosteroid)
Chemotherapy-Induced Nausea
Nausea and vomiting are two of the most feared and most common side effects of chemotherapy. CINV affects up to 40% of patients receiving chemotherapy.
Doctors will prescribe patients antiemetics to take before, during, and after chemotherapy to prevent CINV; unfortunately, research shows that many patients will still experience these side effects.
CINV prophylaxis typically relies on the following types of medications:
- 5-HT3 Antagonists: ondansetron, granisetron, dolasetron, and palonosetron
- NK1 Antagonists: aprepitant and fosaprepitant
- Corticosteroids: dexamethasone
Antiemetic medication recommendations may vary slightly depending on the administered chemotherapeutic agent and the CINV subtype.
Motion Sickness
Motion sickness occurs when the brain receives conflicting signals about movement and balance from the inner ear, eyes, and body. It often happens when traveling in a car or on a boat and triggers symptoms like dizziness, nausea, and vomiting.
Antihistamine and anticholinergic medications are recommended for treating motion sickness. They are most effective when used before or at the first onset of symptoms.
According to the American Academy of Family Physicians, scopolamine should be prescribed as a first-line medication for preventing motion sickness. First-generation antihistamines, such as dimenhydrinate, promethazine, and meclizine, can also be used but are more likely to cause drowsiness as a side effect.
Pregnancy
"Morning sickness" affects up to 80% of pregnant women. The American Academy of Family Physicians recommends using pharmacologic therapy for treating nausea and vomiting during pregnancy only if nonpharmacologic therapies are ineffective.
The ACOG recommends using pyridoxine with or without doxylamine as first-line pharmacotherapy for treating nausea and vomiting caused by pregnancy.
If this is ineffective, other antiemetics that have been used to control nausea and vomiting during pregnancy include:
- Prochlorperazine (dopamine antagonist)
- Ondansetron (5-H3T antagonist)
- Diphenhydramine (antihistamine and anticholinergic)
- Meclizine and dimenhydrinate (antihistamine)
Not all medications are safe during pregnancy. Always consult your doctor before taking over-the-counter or prescription antiemetics to ensure the safety of the developing fetus.
Side Effects and Risks
Side effects can vary depending on the type of antiemetic and range in frequency and severity. Doctors should always review all possible side effects before prescribing these medications.
- Antihistamines and Anticholinergics: drowsiness, constipation, dry mouth, urinary retention
- Dopamine Blockers: fatigue, heart rhythm changes, restlessness, abnormal muscle movements
- Serotonin Blockers: fatigue, headache, constipation, heart issues
- NK1 Blockers: fatigue, weakness, diarrhea, dizziness, hiccups
- Corticosteroids: indigestion, increased appetite, acne, bruising, mood swings, insomnia
- Cannabinoids: changes in mood, thoughts, and perception of reality
Prolonged use of some antiemetics increases the risk of more serious concerns, including:
- Extrapyramidal Symptoms: Dopamine antagonists can cause a variety of movement disorders, such as tardive dyskinesia (involuntary, repetitive movements), akathisia (restlessness), or bradykinesia (slowed movement).
- Cardiovascular Risks: Serotonin antagonists have been associated with QT interval prolongation (a problem with the heart's electrical system), which increases the risk of arrhythmias, fainting, seizures, and cardiac arrest.
When to Consult a Doctor
Contact a doctor if you experience any of the following symptoms when taking an antiemetic medication:
- Severe, persistent, or worsening nausea and vomiting
- Severe constipation
- Muscle weakness
- Abnormal muscle movements
- Irregular heartbeat
- Severe drowsiness
- Confusion
- Signs of an allergic reaction: rash, itching, swelling, severe dizziness, or difficulty breathing
This list is not exhaustive. If you experience any other unusual or severe symptoms, seek medical attention promptly.
Future Trends and Innovations in Antiemetics
The field of antiemetics is continually evolving, with ongoing research aimed at developing more effective and personalized treatments for nausea and vomiting.
One significant area of research is the development of new antiemetic agents targeting different receptors. For example, new drugs targeting opioid, cannabinoid, and peptide YY receptors are being explored.
Another trend is the investigation of novel formulations and delivery methods. For instance, granisetron extended-release subcutaneous injections are being studied for their ability to provide a prolonged therapeutic effect, which may enhance the management of delayed CINV.
Personalized medicine, which tailors treatment based on an individual's genetic makeup, holds promise for optimizing antiemetic therapy. Pharmacogenetics studies how genetic variations affect drug metabolism and response, potentially predicting which antiemetics will be most effective and have the fewest side effects for each patient.
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Key Takeaways
- Antiemetics may help manage nausea and vomiting across a wide range of medical conditions, from motion sickness to chemotherapy-induced symptoms.
- Understanding the different types of antiemetics, their specific uses, and potential side effects is essential for making informed decisions about nausea management.
- While prescription-based and over-the-counter options offer effective relief, natural remedies and complementary therapies provide additional avenues for those seeking alternative approaches.
- As research advances, the development of more targeted and personalized antiemetic treatments promises to further enhance the ability to control these distressing symptoms
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