Generic Drug
Diphenhydramine Hydrochloride


Dosage Forms (Warner Lambert Consumer, Parke-Davis)

Capsules: Benadryl Allergy Kapseals, soft gel 25mg; Dye-free allergy, LiquiGels 25mg
Tablets: Benadryl Allergy 25 mg, Benadryl Allergy ultratab 25mg
Chewable tablets: Benadryl Allergy 12.5mg
Liquid, Dye-Free Allergy: 12.5mg/5ml
Generics also available


  Adult Dosing Guidelines

  • For management of allergic rhinitis, allergic conjunctivitis, uncomplicated allergic skin manifestations of urticaria and angioedema, amelioration of allergic reactions to blood plasma, dermographisms, and as adjunctive therapy in anaphylactic reactions:
    Oral: 25 to 50 mg every 4 to 8 hours. Maximum 300mg/day.
  • For sedation: 50 mg at bedtime.


Pediatric Dosing Guidelines

  • Do not use for children < 6 months old.
  • For the control of allergic manifestations (itch, etc.) or motion sickness: 12.5 mg to 25 mg 3 to 4 times a day or 5mg/kg/day. Maximum 300mg/day.
  • For sedation: 12.5 mg to 25 mg at bedtime.


Triage Questions About Treatment or Related Issues

Do you plan to drive/operate heavy machinery while taking this medication?

Are you taking any other medication (specifically other depressants or alcohol)?

Do you have any other current conditions (asthma, glaucoma, are you nursing)?


General Information

Diphenhydramine competitively inhibits histamine at the H1 receptor site. Antihistamines will prevent, but not reverse, histamine-mediated reactions. It is nonselective, acting on both central and peripheral H1 receptors to decrease reactions such as flaring and itching. Therapeutic effects begin to occur 15-30 minutes after administration and last for 4-6 hours. Peak effects are seen 1-2 hours after administration. Use is contraindicated in patients with lower respiratory tract symptoms (including asthma), nursing women, narrow-angle glaucoma, stenosing peptic ulcer, the elderly and debilitated, and children under 6 months. Caution should be taken with patients with an enlarged prostate causing difficult urination or children under 6. Consult a physician if the patient is nursing or pregnant. Caution should be taken in operating a motor vehicle or heavy machinery.

Adverse Reactions/Side Effects
Drowsiness, rash, nausea, vomiting, blurred vision, excitability in children, perspiration, headache, and dry mouth.

Natural Products or Nutritional Interactions (if applicable)
May be taken with food or milk if GI upset occurs. Avoid alcohol while taking this medication.