Can you drink alcohol on Benadryl?
It's best to avoid alcohol while taking Benadryl — both are sedating, and combining them can leave you dangerously drowsy and impaired.
Why
Benadryl's active ingredient is diphenhydramine, a first-generation (sedating) antihistamine. MedlinePlus states plainly that "alcohol can add to the drowsiness caused by this medication" and advises to "avoid alcoholic beverages while you are taking this medication." Both are central-nervous-system depressants, so their sedating effects stack — meaning more pronounced drowsiness, dizziness, and impaired coordination and judgment than either alone.
What to watch for
Watch for heavy drowsiness, dizziness, confusion, and muscle weakness — do not drive or operate machinery until you know how the combination affects you. The risk is higher in adults 65 and older, for whom diphenhydramine is generally not recommended (falls, confusion). If you take other sedating medicines (opioids, sleep aids, anxiety or muscle-relaxant drugs), are pregnant or breastfeeding, or have a health condition, ask a pharmacist or doctor before combining. Note that many nighttime and PM products (e.g. "Tylenol PM") also contain diphenhydramine, so check labels to avoid doubling up.
This is general reference, not medical advice, and not a guarantee of safety. Interactions depend on your doses, health conditions, and other medicines. Always confirm with your pharmacist or doctor before combining products, and follow the dosing on each label.