The maximum recommended oral dose of diphenhydramine for adults is typically 25 to 50 mg every 4 to 6 hours as needed, not to exceed 300 mg in 24 hours. For intramuscular (IM) or intravenous (IV) administration, the maximum can be up to 400 mg per day, with single doses usually not exceeding 100 mg. Pediatric dosing varies by age and weight but is significantly lower and should be carefully followed as per specific guidelines. For insomnia, a common dose is 50 mg at bedtime. Use in children under 6 years for self- medication is generally not recommended or should be clinically directed. It is important to adhere to these dosing limits to avoid toxicity and adverse effects.