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Most adults can take diphenhydramine 25–50 mg every 4–6 hours, up to 300 mg in 24 hours, unless a prescriber told you differently.

A typical single dose for a 50-pound dog is 50 mg of plain diphenhydramine, often given every 8–12 hours when a veterinarian says it fits.

Most pregnant adults stick to 25–50 mg every 4–6 hours, with a 300 mg max in 24 hours, taken only when symptoms call for it.

Most adults who use diphenhydramine for sleep take 25–50 mg at bedtime; higher doses raise side-effect risk and aren’t a good idea.

Most dogs get 1 mg per lb of diphenhydramine per dose, up to three times daily, only when your vet okays it.

Most dogs get 1 mg per lb of plain diphenhydramine every 8–12 hours, with veterinarian guidance and careful label checks.

Most dogs take diphenhydramine at 2–4 mg/kg every 8–12 hours, but your vet should set the dose for your dog.

A common starting point is 1 mg per pound, so a 20-lb dog often lands near a 20 mg dose, spaced about every 8–12 hours.

A typical single dose for a 15-lb dog is 15 mg of diphenhydramine, spaced at least 8–12 hours apart unless a veterinarian tells you otherwise.

Most 10-lb dogs land near 10 mg diphenhydramine per dose, but the safest number depends on the exact product and your dog’s health.