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Alcohol and Other CNS Depressants Including Barbiturates, Tranquilizers, Hypnotics, Sedatives, Antianxiety Agents, and Narcotic Analgesics: Have additive effects with antihistamines. Dosage adjustments of CNS depressants may be necessary to avoid profound CNS depression.
Monoamine Oxidase Inhibitors (MAOI) (Phenelzine, Tranylcypromine, Isocarboxazid, Furazolidone, Procarbazine): May prolong and intensify the anticholinergic and CNS depressant effects of diphenhydramine. Diphenhydramine should be used with caution wit MAOIs or within two weeks of stopping a MAOI.
Anticholinergic Drugs (e.g., Atropine): May potentiate diphenhydramine's anticholinergic side effects.
β-Blockers (Metoprolol, Carvedilol, Labetalol, Propranolol, Timolol): Diphenhydramine increases the plasma concentrations and cardiovascular effects of these drugs.
PAS (4-Aminosalicylic Acid): Diphenhydramine administration significantly reduces absorption of the antituberculosis agent PAS from the GI tract.
