What is the recommended dosage of Benadryl (diphenhydramine) for adults and children?

Diphenhydramine (Benadryl) Dosage Guidelines

The recommended dosage of diphenhydramine (Benadryl) for adults is 25-50 mg every 4-6 hours, not exceeding 300 mg in 24 hours, while children 6-12 years should receive 25 mg every 4-6 hours, not exceeding 150 mg daily, and it should not be used in children under 6 years of age.

Adult Dosing

• Standard oral dosage: 25-50 mg (10-20 mL of liquid formulation) every 4-6 hours 1
• Maximum daily dose: Do not exceed 6 doses (300 mg) in 24 hours 1
• Duration of effect: 4-6 hours per dose
• Administration: Can be taken with or without food

Pediatric Dosing

• Children 6-12 years: 25 mg (10 mL) every 4-6 hours 1
• Children under 6 years: Not recommended 1
• Maximum daily dose for children 6-12 years: Do not exceed 150 mg in 24 hours (based on adult maximum of 6 doses)

Special Situations

Anaphylaxis (as adjunctive therapy)

• Adults: 25-50 mg IV/IM 2
• Children >12 years: 10 mg IV/IM 2
• Children 6-12 years: 5 mg IV/IM 2
• Children 6 months-6 years: 2.5 mg IV/IM 2
• Infants <6 months: 250 μg/kg IV/IM 2

Note: Diphenhydramine is NOT first-line therapy for anaphylaxis. Epinephrine is the definitive first-line treatment 3.

Sleep Disorders in Children

• Dosage: 1 mg/kg at bedtime has been studied for pediatric sleep disorders 4
• This should only be used under physician supervision and is not an FDA-approved indication

Important Considerations

Safety Concerns

• Diphenhydramine has a narrow therapeutic window, with toxicity possible at doses exceeding 7.5 mg/kg 5
• Children under 6 years should not receive diphenhydramine without specific medical direction due to risk of paradoxical excitation and potential respiratory depression
• Fatal overdoses have been reported, with one documented case involving 7.5 g (150 times the standard adult dose) 6

Potential Side Effects

• Common: Drowsiness, dizziness, dry mouth, blurred vision, constipation
• Severe: Confusion, urinary retention, tachycardia, hallucinations (at higher doses)
• Warning: Recent reports of dangerous "challenges" on social media involving intentional diphenhydramine overdose have resulted in fatalities 7

Precautions

• Use with caution in elderly patients who are more susceptible to anticholinergic effects
• Avoid use with other sedating medications or alcohol
• Patients should avoid driving or operating machinery while taking diphenhydramine
• Patients with narrow-angle glaucoma, prostatic hypertrophy, or urinary retention should use with caution

Clinical Pearls

• Diphenhydramine is primarily used for allergic reactions, but its sedating properties make it a common ingredient in over-the-counter sleep aids
• For allergic reactions, second-generation (non-sedating) antihistamines are preferred for daytime use
• In anaphylaxis management, diphenhydramine is only effective for cutaneous symptoms and should never delay epinephrine administration 3
• The combination of H1 (diphenhydramine) and H2 antagonists (ranitidine) is superior to diphenhydramine alone for urticaria 3

Remember that diphenhydramine is highly effective for acute urticaria, with studies showing prompt relief of symptoms in most patients as long as the medication is continued 8.