Hydroxyzine interacts with a surprisingly long list of medications, supplements, foods, and substances. The most dangerous combinations involve anything that adds to its two main effects: sedation and changes to heart rhythm. Because hydroxyzine is both a strong antihistamine and a central nervous system depressant, doubling up on either of those properties can turn a safe medication into a risky one.
Alcohol and Cannabis
Alcohol is the most common substance people combine with hydroxyzine without realizing the risk. Both slow down brain activity on their own, and together they amplify each other’s effects. Dizziness, extreme drowsiness, and impaired judgment are the predictable results, but in higher amounts the combination can suppress breathing and consciousness more than either substance would alone. Cannabis carries the same type of risk, increasing sedation and cognitive impairment when used alongside hydroxyzine.
Opioid Pain Medications
Combining hydroxyzine with opioids is one of the most dangerous interactions on this list. Opioids like oxycodone, morphine, and fentanyl already carry a risk of respiratory depression, meaning they can slow your breathing to dangerous levels. Adding hydroxyzine on top deepens that sedation and can lead to profound respiratory depression, coma, or death. This isn’t a theoretical risk. Regulatory agencies classify this combination as “generally avoid” and recommend that if it’s absolutely necessary, both drugs should be used at the lowest possible doses for the shortest possible time.
Benzodiazepines and Sleep Medications
Benzodiazepines like alprazolam (Xanax), lorazepam (Ativan), diazepam (Valium), clonazepam (Klonopin), and temazepam (Restoril) all depress the central nervous system. Adding hydroxyzine increases the chance of extreme drowsiness, slowed breathing, and dangerous over-sedation. The same applies to prescription sleep aids like zolpidem (Ambien) and lemborexant (Dayvigo), which work through similar pathways. If you’re taking hydroxyzine for anxiety or sleep, these medications overlap in effect, and the combination can quickly become too much.
Other Antihistamines and Cold Medicines
This catches many people off guard. Hydroxyzine is an antihistamine, so taking another antihistamine on top of it, even an over-the-counter one, stacks up a property called anticholinergic activity. Diphenhydramine (Benadryl) is the biggest concern because it’s strongly anticholinergic on its own and shows up in dozens of nighttime cold, flu, and sleep products. Even cetirizine (Zyrtec) is frequently flagged as a checked interaction.
When anticholinergic effects pile up, the symptoms go well beyond simple drowsiness. You can experience blurred vision, a flushed face, dry mouth, rapid heart rate, constipation, difficulty urinating, and overheating because your body loses its ability to sweat properly. In more severe cases, the central nervous system effects include confusion, hallucinations, disorientation, delirium, and seizures. Before grabbing any allergy pill, sleep aid, or cold medicine from the pharmacy shelf, check the active ingredients for antihistamines.
MAO Inhibitors
Monoamine oxidase inhibitors (MAOIs), a class of antidepressants, can intensify and prolong both the sedative and anticholinergic effects of hydroxyzine. MAOIs interfere with the breakdown of certain brain chemicals, which appears to amplify how strongly hydroxyzine acts on the nervous system. Many manufacturers of sedating antihistamines consider use within 14 days of an MAOI to be contraindicated. Older adults and people with underlying neurological conditions are especially vulnerable to anticholinergic toxicity from this combination.
Drugs That Affect Heart Rhythm
Hydroxyzine can lengthen the QT interval, a measurement of electrical activity in your heart. When the QT interval stretches too far, it raises the risk of a dangerous irregular heartbeat called torsades de pointes, which can be fatal. The European Medicines Agency has made it a formal contraindication to take hydroxyzine alongside any other medication that also prolongs the QT interval.
The list of QT-prolonging drugs is long and spans many categories, from certain antibiotics to antipsychotics to heart medications. Medications that lower potassium levels (some diuretics, for instance) also increase this risk because low potassium makes the heart more vulnerable to rhythm problems. Drugs that slow the heart rate add another layer of concern. If you’re on any cardiac medication, this interaction is worth a specific conversation with your pharmacist.
Certain Antifungals, Antibiotics, and HIV Drugs
Your liver breaks down hydroxyzine using a specific enzyme system called CYP3A4/5. Medications that block this enzyme prevent your body from clearing hydroxyzine efficiently, so the drug builds up in your bloodstream to higher-than-intended levels. Higher levels mean a greater risk of QT prolongation and other side effects. Health Canada’s product monograph lists three major drug classes as contraindicated for this reason: azole antifungals (used for yeast and fungal infections), macrolide antibiotics (a common class of antibiotics), and HIV protease inhibitors. If you’re prescribed any of these while taking hydroxyzine, one of the two medications typically needs to be changed or stopped.
Grapefruit and Grapefruit Juice
Grapefruit inhibits the same liver enzyme that breaks down hydroxyzine. Drinking grapefruit juice or eating grapefruit while on hydroxyzine can raise blood levels of the drug enough to increase the risk of heart rhythm problems. This isn’t a minor footnote. The official product guidance instructs patients to avoid grapefruit and grapefruit-containing products entirely during treatment.
Special Risks for Older Adults
The American Geriatrics Society’s 2023 Beers Criteria lists hydroxyzine as a medication to avoid in older adults, with a “strong” recommendation based on moderate-quality evidence. The reasons are practical: the body clears hydroxyzine more slowly with age, so it lingers longer and hits harder. Its anticholinergic effects, including confusion, dry mouth, constipation, and overheating, are more pronounced in older people. Cumulative exposure to anticholinergic drugs is associated with increased risks of falls, delirium, and dementia, even in younger adults. For older adults already taking other medications with anticholinergic properties, adding hydroxyzine can push that total burden into dangerous territory.