Detailed Diphenhydramine dosage information for adults and children. Includes dosages for Insomnia, Allergic Rhinitis, Allergic Reaction and more; plus renal, liver and dialysis adjustments. Find BENADRYL® dosage information for adults, children, and toddlers and learn how much you and your family should take with our allergy medicine product-dosing guide. Official answer: The maximum safe Benadryl (diphenhydramine) dose for adults is 50 to 100 mg for a single dose with a daily maximum of. The recommended adult Benadryl dosage for allergies is 1 to 2 tablets or capsules by mouth every 4 to 6 hours as needed. You shouldn’t take more than 6 doses (300 mg) in a 24-hour period. Find out how much Benadryl adults and children can safely take, plus essential safety tips and side effects to watch for in this medically-reviewed guide. Giving your child Benadryl? Find the recommended amount of Benadryl to give your child based on age and weight using the St. Louis Children's Hospital Benadryl dosage chart. For adults with common cold symptoms, the typical dosage of Benadryl is 25 to 50 mg (one to two tablets) taken every 4 to 6 hours, or as directed by your doctor.