Loading Calculator...
Please wait a moment
Please wait a moment
Calculate safe diphenhydramine (Benadryl) doses
This calculator is for educational purposes only. Benadryl is NOT recommended for children under 2 years old. It causes significant drowsiness and has anticholinergic effects. Do not use as a sleep aid in elderly patients. Consult a healthcare provider for guidance.
Children's Benadryl Liquid: 12.5mg/5mL | Chewable tablets: 12.5mg each
| Age | Weight | Dose | Liquid | Chewable |
|---|---|---|---|---|
| 2-5 years | 20-44 lbs | 6.25 mg | 2.5 mL | ½ tablet |
| 6-11 years | 45-88 lbs | 12.5-25 mg | 5-10 mL | 1-2 tablets |
| 12+ years | 88+ lbs | 25-50 mg | 10-20 mL | 2-4 tablets |
Do NOT give to children under 2 years old
Diphenhydramine (Benadryl) is a first-generation antihistamine that blocks H1 histamine receptors. It crosses the blood-brain barrier, causing significant drowsiness. It also has anticholinergic effects (dry mouth, urinary retention, constipation).
| Feature | First-Generation (Benadryl) | Second-Generation (Zyrtec, Claritin) |
|---|---|---|
| Drowsiness | Significant | Minimal to none |
| Duration | 4-6 hours | 24 hours |
| Dosing | Every 4-6 hours | Once daily |
| Best for | Acute reactions, nighttime use | Daily allergy control |
| Anticholinergic effects | Significant | Minimal |
This is NOT recommended. Tolerance to the sedative effects develops quickly (often within 3-4 days), requiring higher doses. Long-term use is associated with cognitive impairment and may increase dementia risk in older adults. Consider sleep hygiene improvements or consult a doctor for persistent insomnia.
Peak drowsiness occurs 2-3 hours after taking Benadryl. Effects typically last 4-6 hours, but some people experience "hangover" drowsiness the next morning, especially with higher doses or in elderly patients. Do not drive until you know how it affects you.
While Benadryl is sometimes used off-label for acute anxiety due to its sedating effects, it is not an appropriate treatment for anxiety disorders. The drowsiness and cognitive effects can impair function, and tolerance develops quickly. Proper anxiety treatment should be discussed with a healthcare provider.
Infants and toddlers are at higher risk for serious side effects including paradoxical excitability, seizures, and respiratory depression. The FDA does not recommend OTC antihistamines for children under 2. For allergies in this age group, consult a pediatrician.
Benadryl interacts with many medications, especially those that cause drowsiness (sleep aids, pain medications, anxiety medications, alcohol). It also has anticholinergic effects that can add to similar effects of other medications. Always check with a pharmacist.
For daytime allergies, Zyrtec (cetirizine) or Claritin (loratadine) are better choices because they cause less drowsiness and last 24 hours. Benadryl works faster for acute reactions and may be preferred at bedtime. Benadryl is often used for acute allergic reactions due to its stronger, faster effect.
Seek immediate medical attention if you experience: