What is the recommended dose of Benadryl (diphenhydramine)?

Benadryl (Diphenhydramine) Dosing

For adults and children over 12 years, the standard dose is 25-50 mg orally every 4-6 hours, not exceeding 6 doses in 24 hours; for children 6-12 years, use 25 mg every 4-6 hours; and do not use in children under 6 years for over-the-counter indications. 1

Standard Oral Dosing by Age

• Adults and children ≥12 years: 25-50 mg (10-20 mL) every 4-6 hours 1
• Children 6 to <12 years: 25 mg (10 mL) every 4-6 hours 1
• Children <6 years: Do not use 1
• Maximum frequency: Do not exceed 6 doses in 24 hours for any age group 1

Special Clinical Applications

Acute Dystonic Reactions

• Dose: 1-2 mg/kg IV/IM (maximum initial dose: 50 mg) 2
• Critical warning: Rapid IV administration may precipitate seizures 2
• Side effects: May cause sedation, respiratory suppression, hypotension, and paradoxical excitement 2

Breakthrough Antiemetic (Chemotherapy-Induced)

• Dose: 25-50 mg PO or IV every 4-6 hours as needed for dystonic reactions from other antiemetics 2
• Alternative: Benztropine 1-2 mg IV/IM if allergic to diphenhydramine 2

Elderly Patients: Dose Reduction Required

Patients over 85 years should receive reduced doses due to increased anticholinergic sensitivity. 2

• Higher risk of cognitive impairment, delirium, and falls in elderly patients 2, 3
• Consider alternative non-sedating antihistamines when sedation is a concern 2, 3
• For insomnia in elderly: Consider doxepin 3-6 mg instead of diphenhydramine 2, 3

Critical Warnings and Contraindications

Not Recommended for Insomnia

• The American Academy of Sleep Medicine explicitly recommends against using diphenhydramine for sleep onset or sleep maintenance insomnia 2, 3
• Mean sleep latency reduction of only 8 minutes versus placebo 2
• Total sleep time improvement of only 12 minutes versus placebo 2
• No improvement in quality of sleep compared to placebo 2

Toxicity Thresholds

• Children <6 years: Refer to emergency department if ingestion ≥7.5 mg/kg 4
• Patients ≥6 years: Refer to emergency department if ingestion ≥7.5 mg/kg or ≥300 mg (whichever is less) 4

Important Anticholinergic Side Effects

Monitor for the following adverse effects, especially in elderly patients:

• Central nervous system: Confusion, delirium, impaired psychomotor performance 2, 3
• Peripheral anticholinergic: Dry mouth, blurred vision, urinary retention, constipation 2, 3
• Cardiovascular: Hypotension, tachycardia, and cardiac toxicity risk with rapid IV administration 2, 5
• Falls risk: Particularly concerning in elderly populations 2, 3

Monitoring Requirements

• Monitor for changes in mental status or excessive sedation 2, 3
• Assess falls risk, especially in elderly 2, 3
• Watch for urinary retention and constipation 2, 3

Clinical Pitfalls to Avoid

• Never administer IV diphenhydramine rapidly due to increased risk of seizures and cardiovascular effects 2
• Avoid in elderly patients when possible; consider second-generation antihistamines instead 3, 5
• Do not use for insomnia given lack of efficacy and significant side effect profile 2, 3
• Be aware of topical toxicity: Lethal concentrations can occur from excessive topical application, particularly in children 6