The official answer is none. The FDA-mandated label on Benadryl (diphenhydramine) reads: “Avoid alcoholic beverages while taking this product.” This isn’t a soft suggestion. Both substances slow down your central nervous system, and combining them amplifies effects like drowsiness, dizziness, impaired coordination, and difficulty breathing in ways that are unpredictable and potentially dangerous.
Why the Combination Is Dangerous
Benadryl and alcohol both depress your central nervous system, which controls breathing, heart rate, and coordination. When you take them together, each one intensifies the other’s sedating effects. This isn’t a simple case of 1 + 1 = 2. The interaction is additive, meaning the drowsiness, slowed reflexes, and mental fog you’d get from either substance alone can become significantly worse when they overlap in your system.
The risks of this combination include drowsiness, dizziness, fainting, loss of coordination, nausea and vomiting, difficulty breathing, and an increased risk of overdose. For older adults especially, this combination can lead to falls and serious injuries.
Benadryl Alone Can Impair You More Than Alcohol
Most people underestimate how sedating Benadryl is on its own. A study using a driving simulator found that a single 50 mg dose of diphenhydramine (the standard two-tablet dose) impaired driving performance more than having a blood alcohol concentration of 0.10%, which is above the legal limit in every U.S. state. Participants on Benadryl had worse lane keeping, more steering instability, and greater drowsiness than those given alcohol. Now imagine stacking actual alcohol on top of that level of impairment.
How Long Benadryl Stays in Your System
Benadryl’s half-life in adults is roughly 9 hours, with a range of 7 to 12 hours. “Half-life” means it takes that long for your body to eliminate just half the drug. A general pharmacology rule is that it takes about 4 to 5 half-lives for a drug to be mostly cleared from your system. For Benadryl, that works out to roughly 36 to 60 hours in a healthy adult.
This doesn’t mean you need to wait two full days before having a drink, since the sedating effects wear off well before the drug is fully eliminated. But it does mean the drug lingers longer than most people assume. If you took Benadryl before bed, it’s still active in your system the next morning, and having a mimosa at brunch could hit harder than you’d expect.
In older adults, the half-life stretches to about 13.5 hours on average, and can reach up to 18 hours. The drug is processed primarily by the liver, the same organ responsible for metabolizing alcohol. When both substances compete for your liver’s attention, each one can stick around longer.
Who Faces the Greatest Risk
Older adults are the most vulnerable group. The longer half-life means diphenhydramine builds up more easily, and age-related changes in balance and cognition make the sedating effects more consequential. Falls are a specific and serious concern. A stumble that a 25-year-old shakes off can mean a broken hip or head injury for someone over 65.
People taking other sedating medications face compounded risk as well. If you’re on sleep aids, anti-anxiety medications, tranquilizers, or any other drug that causes drowsiness, adding alcohol to the mix creates multiple layers of central nervous system depression. The more sedating substances in your system at once, the greater the chance of dangerously slowed breathing or loss of consciousness.
What This Means Practically
If you’ve taken a standard dose of Benadryl for allergies or sleep and you’re wondering whether you can have a glass of wine later that evening, the safest answer is to skip the drink. The sedating effects of Benadryl peak within 1 to 3 hours but persist for 4 to 6 hours, and the drug remains active in your body well beyond that window.
If you know you’ll be drinking, consider using a non-drowsy antihistamine instead. Second-generation antihistamines like cetirizine (Zyrtec) or loratadine (Claritin) cause far less sedation and carry a lower interaction risk with alcohol, though they aren’t completely free of it either.
If you’ve already combined the two and feel excessively drowsy, dizzy, confused, or are having trouble breathing, those are signs the interaction is hitting hard. Don’t drive, operate machinery, or put yourself in any situation where impaired coordination could be dangerous.