while it's true you can get diphenhydramine (benadryl) as a prescription the issue isn't so much about the dosage (amount or number of milligrams) as it is about the delivery method. "prescription" diphenhydramine often is delivered intravenously while over-the-counter diphenhydramine is delivered orally or as a skin cream (topically). the usual adult dose of oral diphenhydramine is 25mg to 50mg. it would be unwise to exceed 50mg of diphenhydramine if for no other reason that it causes extreme drowsiness. also people with certain medical conditions should not take diphenhydramine. if you have any questions about prescription or over-the-counter (otc) medications you can always consult a pharmacist. they're the experts when it comes to dosing side effects and every other aspect of medications. please do not play backyard chemist by trying to create "prescription strength" medications from otc versions. it's very dangerous. hope this helps!
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