Benadryl (Diphenhydramine) at a glance: schedule, half-life, and class
- Generic name
- Diphenhydramine hydrochloride or citrate
- Brand names
- Benadryl, ZzzQuil, Unisom SleepGels; in Tylenol PM and Advil PM
- Drug class
- First-generation H1 antihistamine; anticholinergic
- US legal status
- Over the counter; not controlled
- Uses
- Allergies, hives, itching, occasional sleeplessness, motion sickness, cough
- Forms
- Tablets, capsules, liquid, creams, injection
- Onset
- 15 to 60 minutes
- Half-life
- About 3 to 9 hours; up to 13 hours in older adults
Benadryl uses: what diphenhydramine is prescribed for
Diphenhydramine relieves sneezing, runny nose, itching, and hives, and is used for occasional sleeplessness, motion sickness, and, by injection, severe allergic reactions alongside epinephrine.[1]
It crosses into the brain, causing drowsiness, and blocks acetylcholine, causing dry mouth and confusion. Newer antihistamines such as cetirizine and loratadine cause much less sedation.[1]
How much diphenhydramine is safe to take?
These directions come from the over-the-counter Drug Facts label. Do not take more than directed.[1]
| Product or group | Label directions | Notes |
|---|---|---|
| Allergies, adults and children 12 and over | 25 to 50 mg every 4 to 6 hours | No more than 6 doses in 24 hours |
| Sleep aid, adults | 50 mg at bedtime | Not for more than 2 weeks without medical advice |
| Children under 6 | Only on a clinician's advice | Do not use to make a child sleepy |
Benadryl (diphenhydramine) side effects and risks
Common side effects include drowsiness, dizziness, dry mouth, constipation, blurred vision, and trouble urinating.[1]
High doses: in 2020 the FDA warned that taking more than the recommended dose can cause serious heart problems, seizures, coma, and death, after reports of teenagers taking it in a social media challenge.[2]
Older adults: confusion, falls, and urinary retention are common. It is on lists of medicines older adults should avoid, and long-term use of anticholinergic medicines has been linked to higher dementia risk.
Next-day effects: impaired driving can last into the next morning.
Benadryl interactions: what not to mix with diphenhydramine
Choose what it would be combined with:
| Combined with | What happens | Guidance |
|---|---|---|
| Alcohol | More drowsiness and impairment | Avoid |
| Opioids, benzodiazepines, sleep medicines | Additive sedation and slowed breathing | Use caution |
| Other anticholinergic drugs (tricyclics, bladder medicines, other antihistamines) | Confusion, overheating, urinary retention | Avoid doubling |
| Other products containing diphenhydramine or acetaminophen | Accidental overdose | Check all labels |
This is not a full list. A pharmacist can check a complete medication list, including supplements and over-the-counter products.[1]
Benadryl overdose: signs of diphenhydramine overdose and what to do
Overdose causes the anticholinergic toxidrome: hot, dry, flushed skin, dilated pupils, fast heartbeat, agitation, confusion, and hallucinations. Severe cases cause seizures, abnormal heart rhythms, and death.[2]
If someone may have taken too much
- Call 911 for fainting, a seizure, chest pain, a racing or irregular heartbeat, confusion, or if the person cannot be woken.
- If the person collapses and is not breathing normally, start CPR and use an AED if one is available.
- Give naloxone if opioids could be involved. It is safe even if they are not.
- For advice when the person is awake and stable, call Poison Help at 1-800-222-1222 (US, free, 24 hours). Bring the product packaging to the hospital.
Can you become dependent on diphenhydramine?
Tolerance to its sleep effect develops within days, and nightly users may have trouble sleeping when they stop. Rarely, people misuse high doses for hallucinations.[1]
- Nights 1 to 3Rebound insomniaTrouble falling asleep after nightly use.
- Days 1 to 7Possible symptomsRestlessness, irritability, and, after heavy use, nausea and anxiety.
- 1 to 2 weeksSettlesSleep usually returns to normal.
Cognitive behavioral therapy for insomnia (CBT-I) is the most effective long-term treatment for chronic insomnia.
How do you buy diphenhydramine safely in the US?
Diphenhydramine is sold over the counter without a prescription at pharmacies, groceries, and convenience stores.
- Cost: generic diphenhydramine is inexpensive.
- Check labels: it is in many combination products, such as nighttime pain relievers and cold medicines.
- Ask a pharmacist: a pharmacist can check whether it is safe with your other medicines and health conditions.
Can you buy diphenhydramine online?
Yes. Diphenhydramine is sold online by regular retailers. Follow the Drug Facts label and avoid taking several products that contain it.
The FDA's BeSafeRx tool explains how to recognize a safe online pharmacy.[3]
Is Benadryl legal? Diphenhydramine legal status in other countries
| Country | Status |
|---|---|
| United Kingdom | Pharmacy medicine |
| Canada | Non-prescription medicine |
| International | Not under UN control |
Laws change and differ in detail. Check current rules before carrying any controlled medicine across a border.[4]
Common questions about Benadryl (diphenhydramine)
Is Benadryl safe for sleep every night?
It is meant for occasional use. Tolerance develops quickly, and nightly use is not recommended, especially for older adults.
What is the Benadryl challenge?
A social media trend encouraging people to take large doses to hallucinate. It has caused seizures, heart problems, and deaths.
How much Benadryl is too much?
More than 300 mg a day for adults is above the label maximum; serious toxicity can occur at roughly 1 gram or more, and less in children.
Can I give Benadryl to my child to help them sleep?
No. Do not use it to make a child sleepy, and ask a clinician before using it in children under 6.
Is Benadryl (diphenhydramine) the same as Unisom?
Unisom SleepGels contain diphenhydramine; Unisom SleepTabs contain doxylamine, a related antihistamine.
Sources
- Benadryl (diphenhydramine) prescription information. DailyMed, US National Library of Medicine.
- FDA warns about serious problems with high doses of the allergy medicine diphenhydramine (Benadryl). US Food and Drug Administration, 2020.
- BeSafeRx: Your Source for Online Pharmacy Information. US Food and Drug Administration.
- International drug control conventions. United Nations Office on Drugs and Crime.
