A 100-lb dog often lands near 100 mg per dose, but the right amount hinges on the product, your dog’s health, and your veterinarian’s directions.

For a 10-pound dog, many vets use diphenhydramine at about 10 mg per dose, given every 8–12 hours when it fits the case.

In a 1-year-old, diphenhydramine dosing is weight-based, and many pediatric sources say to use it only when a clinician tells you to.

A 2-year-old should get diphenhydramine only with clinician direction, and the dose must match weight and product strength.

Most dogs get 1 mg per lb of diphenhydramine every 8–12 hours, but your vet should set the dose for your dog.

Many dogs are dosed at about 1 mg of diphenhydramine per pound per dose, yet timing and safety checks matter just as much.

For most adults, diphenhydramine sleep-aid labels point to 50 mg at bedtime, yet it’s a poor fit for frequent insomnia and a bad idea for kids.

Most adults take 25–50 mg of diphenhydramine every 4–6 hours for hives, staying within the product’s daily limit on the Drug Facts label.

Diphenhydramine is usually not given to babies; if it’s ever used, a clinician sets a weight-based dose for the exact liquid strength you have.

Most adults use 25–50 mg of diphenhydramine at bedtime, starting with 25 mg, and treating 50 mg as the usual one-dose ceiling for sleep.