What is the dosage for Diphenhydramine? Diphenhydramine doses vary depending on formulation, and has its maximal effect about one hour after it is taken.

  • When used to treat insomnia, it is prescribed at bedtime. Indivduals over the age of 60 years are especially sensitive to the sedating and anticholinergic effects of diphenhydramine, and the dose should be reduced.
  • A common regimen for treating adult allergic reaction is 25-50 mg every 4-6 hours not to exceed 300 mg daily.
  • Insomnia is treated with 50 mg taken 30 minutes before bedtime.