NutriStack
Alcohol and Diphenhydramine, a caution.
Alcohol can add to diphenhydramine's sedating and anticholinergic effects. Human testing found worse mental-performance impairment when ethanol was combined with diphenhydramine, and driving-simulator work shows diphenhydramine can impair driving substantially. The combination is especially risky before driving, in older adults, or when any other sedating medication is also present.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
Same shape as the other 1,729 pairs in the public database.
From the interaction database
What the row says.
Every entry follows the same shape: what is happening, the mechanism, the recommendation, and the primary literature.
At a glance
- Substances
- Alcohol and Diphenhydramine
- Pair type
- Caution
- Evidence (highest tier)
- Strong
- Source citations
- 2 sources
- Stack Score effect
- −5 to your Stack Score (per scored caution row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Caution · Strong evidence
Caution
What is happening. Alcohol can add to diphenhydramine's sedating and anticholinergic effects. Human testing found worse mental-performance impairment when ethanol was combined with diphenhydramine, and driving-simulator work shows diphenhydramine can impair driving substantially. The combination is especially risky before driving, in older adults, or when any other sedating medication is also present.
Mechanism. Diphenhydramine crosses the blood-brain barrier and blocks central H1 and muscarinic receptors, causing sedation, slowed reaction time, and impaired attention. Alcohol independently depresses CNS arousal and motor coordination, so the combined pharmacodynamic effect can exceed either substance alone.
Recommendation. Avoid alcohol when you take diphenhydramine, including nighttime sleep-aid doses. Do not drive, operate machinery, or take extra sedatives if both were used the same day. Seek help for severe confusion, extreme sleepiness, falls, or trouble breathing.
Sources (2)
- Baugh R, Calvert RT. The effect of diphenhydramine alone and in combination with ethanol on histamine skin response and mental performance. Eur J Clin Pharmacol. 1977;12(3):201-204. PMID 22437
- Weiler JM, Bloomfield JR, Woodworth GG, et al. Effects of fexofenadine, diphenhydramine, and alcohol on driving performance: a randomized, placebo-controlled trial in the Iowa driving simulator. Ann Intern Med. 2000;132(5):354-363. PMID 10691585
Stack Score
How this pair moves the number.
Effect on the composite score
If both Alcohol and Diphenhydramine are in the same stack, this pair applies −5 to your Stack Score (per scored caution row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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