Understanding Cyclizine: What It Is and How It Works
Cyclizine is a first-generation antihistamine medication primarily used to prevent and treat nausea, vomiting, and dizziness [1.2.6, 1.8.3]. Its applications are diverse, ranging from managing motion sickness and vertigo to alleviating symptoms after surgery or from other medications like opioids [1.2.6, 1.8.3]. It functions by blocking histamine H1 receptors in the brain's vomiting center, which helps to suppress the signals that cause feelings of sickness [1.8.4, 1.8.5]. Additionally, cyclizine has anticholinergic properties, meaning it blocks the neurotransmitter acetylcholine. This action further helps in reducing nausea by affecting the vestibular system (the body's balance center) and the chemoreceptor trigger zone (CTZ) in the brain [1.8.2, 1.8.5]. Its effects typically begin within 30 to 60 minutes of oral administration and last for about four to six hours [1.3.1, 1.8.4]. While effective, its anticholinergic and sedative properties are the reason for many of its contraindications and necessary precautions.
Absolute Contraindications: When Not to Take Cyclizine
There are several absolute contraindications for cyclizine, meaning it should not be used by individuals with these conditions due to the high risk of serious adverse effects. An absolute contraindication is an allergy or hypersensitivity to cyclizine or any of its components [1.2.3, 1.3.3]. It is also contraindicated for patients in a state of acute alcohol intoxication, as the anti-emetic properties can mask and potentially increase the toxicity of alcohol [1.3.3, 1.7.5]. Furthermore, cyclizine should not be given to children under the age of six unless specifically directed by a doctor [1.3.6, 1.5.1].
Medical Conditions Requiring Caution
Due to its anticholinergic effects, cyclizine must be used with caution in people with a range of pre-existing medical conditions. The medication can exacerbate these issues, leading to potentially dangerous complications. Consulting a doctor or pharmacist before taking cyclizine is essential if you have any of the following:
Eye and Urinary Conditions
- Angle-Closure Glaucoma: Cyclizine can increase pressure inside the eye, which is dangerous for individuals with this type of glaucoma [1.2.3, 1.6.4]. Symptoms of a problem can include sudden eye pain or blurred vision [1.6.3].
- Prostate Enlargement and Urinary Retention: The drug's anticholinergic effects can make it difficult to urinate, worsening problems for those with an enlarged prostate or existing urinary retention issues [1.2.1, 1.6.4].
Respiratory and Cardiovascular Issues
- Breathing Problems: Patients with conditions like asthma, emphysema, or chronic obstructive pulmonary disease (COPD) should use cyclizine cautiously. The medication can cause bronchial secretions to thicken, potentially obstructing the respiratory tract [1.2.1, 1.3.3].
- Heart Failure and High Blood Pressure: Cyclizine is contraindicated in patients with severe heart failure [1.6.5]. It may cause a drop in cardiac output and changes in heart rate and blood pressure, which can be risky for those with hypertension or after a recent heart attack [1.2.3, 1.6.5].
Other Significant Health Conditions
- Liver Disease: Since cyclizine is metabolized by the liver, individuals with liver problems may experience exaggerated sedative effects [1.2.6]. Severe liver disease is a contraindication as it can increase the risk of coma [1.6.5].
- Epilepsy: Cyclizine should be used with caution in people with epilepsy or other conditions that cause seizures, as it may lower the seizure threshold [1.2.3].
- Bowel Obstruction Risk: Conditions such as Crohn's disease, diverticulitis, or hernias can lead to bowel obstruction, and cyclizine may worsen this risk [1.2.3].
- Porphyria: This rare, inherited blood disorder is another condition where cyclizine should be avoided [1.2.3, 1.6.1].
- Phaeochromocytoma: This is a rare tumor of the adrenal gland, and caution is advised when prescribing cyclizine to patients with this condition [1.6.4, 1.6.5].
Significant Drug Interactions to Avoid
Cyclizine can interact with numerous other substances, leading to increased side effects or altered efficacy. It is crucial to inform your doctor of all medications you are taking.
CNS Depressants and Alcohol
Combining cyclizine with alcohol or other Central Nervous System (CNS) depressants significantly increases the risk of drowsiness, dizziness, and impaired coordination [1.7.1, 1.7.3]. This includes:
- Alcohol: Should be avoided as it potentiates the sedative effects [1.7.2, 1.8.4].
- Sedatives and Tranquilizers: Concurrent use is not recommended [1.2.1].
- Opioid Pain Medications: Additive CNS depressant effects can occur [1.4.5, 1.4.6].
- Sleeping Pills: Increases sedation [1.4.5].
Other Anticholinergic and Specific Medications
Taking cyclizine with other drugs that have anticholinergic properties can intensify side effects like dry mouth, blurred vision, and urinary retention [1.2.1].
- Monoamine Oxidase Inhibitors (MAOIs): This class of antidepressants can interact negatively with cyclizine [1.4.4].
- Other Antihistamines: Using multiple antihistamines (e.g., in cold and cough remedies) can lead to additive side effects [1.4.5].
- Certain Antidepressants: Tricyclic antidepressants like amitriptyline can have additive sedative and antimuscarinic effects [1.4.6].
- Drugs that prolong the QT interval: A vast number of drugs, from certain antibiotics to anti-arrhythmics, can interact with cyclizine and increase the risk of heart rhythm problems [1.4.1].
Cyclizine vs. Other Common Antiemetics: A Comparison
| Feature | Cyclizine | Ondansetron (Zofran) | Promethazine (Phenergan) |
|---|---|---|---|
| Drug Class | 1st Gen Antihistamine, Anticholinergic [1.2.6] | 5-HT3 Receptor Antagonist [1.9.3] | 1st Gen Antihistamine, Phenothiazine [1.8.4] |
| Primary Mechanism | Blocks histamine and muscarinic receptors in the brain [1.8.5] | Selectively blocks serotonin receptors in the gut and brain | Blocks dopamine and histamine receptors in the brain |
| Key Uses | Motion sickness, vertigo, post-op nausea [1.2.6] | Chemotherapy-induced and post-op nausea/vomiting [1.9.1] | Nausea/vomiting, sedation, allergies |
| Common Side Effects | Drowsiness, dry mouth, blurred vision [1.2.2] | Headache, constipation, diarrhea | Significant drowsiness, dizziness, confusion |
| Main Contraindication | Angle-closure glaucoma, severe heart failure [1.6.4, 1.6.5] | Hypersensitivity, congenital long QT syndrome | Comatose states, significant respiratory depression |
Special Populations: Pregnancy, Breastfeeding, and Elderly
- Pregnancy: While sometimes used off-label for severe morning sickness (hyperemesis gravidarum), manufacturers generally advise avoiding cyclizine during pregnancy as its safety has not been definitively established [1.2.6, 1.3.3]. Patients should consult their doctor [1.2.4].
- Breastfeeding: Cyclizine is not recommended for breastfeeding women as it can pass into breast milk and may cause side effects in the infant or inhibit lactation [1.3.1, 1.3.3].
- Elderly: Individuals over 65 may have a stronger reaction to cyclizine, experiencing more pronounced dizziness, sedation, dry mouth, and confusion. A smaller dose may be necessary [1.2.2, 1.5.3].
Conclusion: Prioritizing Safety with Cyclizine
Cyclizine is an effective medication for controlling nausea and vomiting from various causes. However, its powerful mechanism of action means it is not suitable for everyone. Understanding when not to take cyclizine is vital for safe use. Always disclose your full medical history and current medication list to a healthcare provider before starting treatment. People with glaucoma, severe heart failure, prostate issues, and certain respiratory conditions, as well as those taking other CNS depressants, must exercise extreme caution or avoid the drug altogether. By respecting these contraindications and warnings, patients can mitigate the risks and use cyclizine safely and effectively when appropriate.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a healthcare professional before starting or stopping any medication.
