Diphenhydramine is an antihistamine commonly used to relieve symptoms of allergies, such as sneezing, runny nose, watery eyes, and itching. It is also used to treat insomnia, motion sickness, and some symptoms of Parkinson's disease (such as tremors) or drug-induced extrapyramidal symptoms. As an over-the-counter (OTC) medication, it is widely available under various brand names, most notably Benadryl, and in many combination cold and flu preparations. It is a first-generation antihistamine, meaning it readily crosses the blood-brain barrier, contributing to its sedative effects.
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Known interactions
Category rule: supplement × medication
Note
Some supplements change how the body processes medications (absorption, liver enzymes, or additive effects).
Specific pairs are checked against a licensed drug database and shown with their own severity. Always confirm with your provider or pharmacist.
Category rule: vitamin × medication
Note
Certain vitamins interact with specific medications (e.g., vitamin K with blood thinners).
Specific pairs are checked against a licensed source; confirm with your provider.
Compound-pair rule
Note
Additive sedation possible.
Start at low melatonin dose (0.3–1 mg) when combined with prescription sedatives.
Frequently asked
Sources referenced
["NIH Office of Dietary Supplements (ODS)", "MedlinePlus", "PubChem", "Mayo Clinic", "FDA (Food and Drug Administration) label information", "DrugBank"]
DoseRoutine compiles summaries from publicly available scientific and regulatory references. Always verify important decisions with a licensed clinician.
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