Understanding Cyclizine and Its Function
Cyclizine is a first-generation antihistamine primarily used to prevent and treat nausea, vomiting, and dizziness associated with motion sickness and vertigo [1.8.5, 1.9.2]. It is part of the piperazine derivative family and works by blocking histamine H1-receptors [1.5.1, 1.5.2]. Its mechanism of action also involves effects on the vestibular system and the chemoreceptor trigger zone in the brain, which helps to inhibit the vomiting reflex [1.4.3, 1.5.2]. Additionally, cyclizine has central anticholinergic (antimuscarinic) and central nervous system (CNS) depressant properties, which contribute to both its therapeutic effects and its potential for drug interactions [1.4.1, 1.5.2]. While effective, these properties mean that cyclizine must be used with caution alongside other medications.
Major Drug Interactions with Cyclizine
Taking cyclizine with certain other drugs can increase the risk of side effects or alter the effectiveness of the medications. The primary interactions to be aware of involve drugs that have similar effects on the body, namely CNS depressants and drugs with anticholinergic properties.
Central Nervous System (CNS) Depressants
Cyclizine itself is a CNS depressant, which means it can cause drowsiness and impair mental and physical abilities [1.4.4]. When combined with other CNS depressants, these effects can become dangerously amplified [1.4.5]. This additive effect increases the risk of extreme sedation, respiratory depression, and significant impairment of coordination and judgment [1.4.4, 1.3.2].
Examples of CNS depressants to avoid or use with extreme caution:
- Alcohol: Combining alcohol with cyclizine can potentiate the toxic effects of alcohol and significantly increase drowsiness [1.2.4, 1.8.4].
- Opioid Analgesics: Medications like codeine, morphine, and oxycodone can have additive depressant effects with cyclizine [1.4.5, 1.2.1].
- Benzodiazepines: Drugs such as diazepam (Valium) and alprazolam (Xanax) can lead to a severe increase in CNS depression when taken with cyclizine [1.2.1, 1.2.2].
- Sleeping Pills (Hypnotics): The sedative effects are compounded, leading to excessive drowsiness [1.2.5].
- Certain Antidepressants: Tricyclic antidepressants like amitriptyline and antipsychotics like chlorpromazine can increase CNS depression [1.2.1].
- Muscle Relaxers: Carisoprodol and baclofen may increase adverse effects [1.2.1].
Anticholinergic (Antimuscarinic) Drugs
Cyclizine possesses anticholinergic properties, which are responsible for side effects like dry mouth, blurred vision, constipation, and urinary retention [1.5.1, 1.9.2]. When taken with other medications that also have anticholinergic effects, these side effects can become more pronounced and severe [1.4.5, 1.5.5].
Examples of drugs with anticholinergic properties:
- Other Antihistamines: Combining first-generation antihistamines like diphenhydramine or promethazine is not recommended.
- Antispasmodics: Medications used for stomach cramps.
- Tricyclic Antidepressants: For example, amitriptyline and desipramine [1.2.1].
- Medications for Overactive Bladder: Such as oxybutynin.
- Some Antipsychotics: For example, clozapine and chlorpromazine [1.2.1].
- Scopolamine: Another medication used for motion sickness [1.2.5].
Monoamine Oxidase Inhibitors (MAOIs)
MAOIs are a class of antidepressants that can have significant interactions with many other medications. Combining an MAOI, such as phenelzine, with cyclizine can intensify the anticholinergic and CNS depressant effects, making side effects worse [1.6.1]. It is generally recommended to avoid this combination.
Drugs that Affect Heart Rhythm (QTc Prolongation)
While some sources state cyclizine itself is not typically associated with QT prolongation, a dangerous heart rhythm condition, it can interact with numerous drugs that do carry this risk [1.7.5, 1.7.1]. Taking cyclizine with drugs known to prolong the QTc interval—such as certain anti-arrhythmics (amiodarone), antibiotics (azithromycin, ciprofloxacin), and antipsychotics (clozapine)—can increase the risk or severity of this effect [1.7.1]. It is crucial to inform your doctor about all medications you are taking.
Comparison of Interacting Drug Classes
| Drug Class | Primary Risk of Interaction with Cyclizine | Example Medications |
|---|---|---|
| CNS Depressants | Additive sedation, drowsiness, impaired coordination, respiratory depression [1.4.5]. | Alcohol, Opioids (Codeine, Morphine), Benzodiazepines (Diazepam) [1.2.4, 1.2.1]. |
| Anticholinergic Drugs | Increased dry mouth, blurred vision, constipation, urinary retention [1.4.5]. | Scopolamine, Tricyclic Antidepressants (Amitriptyline), some Antipsychotics [1.2.5, 1.2.1]. |
| MAOIs | Intensified CNS depressant and anticholinergic side effects [1.6.1]. | Phenelzine, Isocarboxazid [1.6.1, 1.6.2]. |
| QTc-Prolonging Drugs | Increased risk of dangerous heart rhythm problems (arrhythmias) [1.7.1]. | Amiodarone, Azithromycin, Citalopram, Clozapine [1.7.1]. |
Conclusion
To ensure your safety when taking cyclizine, it is vital to be aware of what medications you can not take with it. The most significant interactions occur with other CNS depressants, drugs with anticholinergic properties, and MAOIs, as these can dangerously amplify side effects like drowsiness, confusion, and dry mouth, and in some cases lead to more severe outcomes like respiratory depression or urinary retention. Always consult with a doctor or pharmacist before starting cyclizine, and provide them with a complete list of all your current medications, including over-the-counter drugs and supplements [1.8.3].
For more detailed drug interaction information, you can consult authoritative sources like the NHS (National Health Service).
