Using Benadryl in Emergencies When an EpiPen Isn’t Available
When someone is experiencing a severe allergic reaction—known as anaphylaxis—the gold standard treatment is an epinephrine injection, commonly delivered with an EpiPen. Epinephrine works fast to reverse the dangerous symptoms of anaphylaxis, such as swelling of the airways, a drop in blood pressure, and hives.
But what happens if an EpiPen isn’t available?
In a desperate situation, Benadryl (diphenhydramine) can be used as a temporary measure—not a replacement for epinephrine—while you call 911 immediately and wait for emergency responders.
⚠️ Key Message First:
Benadryl is NOT a substitute for an EpiPen. It works much more slowly and cannot treat life-threatening symptoms like airway closure or shock. Always call emergency services immediately during a serious allergic reaction.
Why Benadryl Might Help in the Meantime
Benadryl’s Mechanism of Action:
Benadryl (diphenhydramine) is an antihistamine, which means it blocks the effects of histamine, a chemical your immune system releases during an allergic reaction.
- Histamine causes many of the classic allergy symptoms: itching, hives, runny nose, and swelling.
- Diphenhydramine works by binding to histamine H1 receptors, preventing histamine from triggering inflammation in tissues.
- This can help reduce skin reactions (like hives), itching, and some mild swelling.
However, it does not:
- Reverse airway constriction quickly.
- Raise dangerously low blood pressure.
- Act fast enough to stop full-blown anaphylaxis.
What You Should Do If There’s No EpiPen
- Call 911 Immediately.
- Time is critical in anaphylaxis. Even if you’re unsure, it’s better to treat it like an emergency.
- Administer Benadryl (diphenhydramine).
- Use oral tablets or liquid if the person can swallow safely.
- Dosage (Adults): 25–50 mg orally.
- If available, liquid diphenhydramine is absorbed a little faster than tablets.
- Monitor Breathing and Circulation.
- If the person has trouble breathing or collapses, be ready to perform CPR if needed.
- Keep the Person Lying Down, Legs Elevated.
- This can help maintain blood flow to vital organs if blood pressure is dropping.
- Wait for Emergency Help.
- Even if the person seems to be improving, they may rebound or worsen again—this is known as biphasic anaphylaxis.
Why It’s Not Enough
Benadryl starts working within 15–30 minutes, but that’s far too slow in a rapidly progressing anaphylactic reaction, where seconds count.
- Epinephrine acts within minutes, targeting:
- Alpha-receptors: Constricts blood vessels to raise blood pressure.
- Beta-1 receptors: Stimulates the heart.
- Beta-2 receptors: Relaxes the muscles around the airways.
Benadryl does none of that—it only deals with the histamine component.
Final Takeaway
If someone is having a severe allergic reaction and no EpiPen is available:
- Call 911 immediately.
- Give Benadryl if the person is conscious and can swallow.
- But don’t rely on it to save their life—emergency care is still essential.
And afterward, make sure the person talks to their doctor about getting a prescription for an EpiPen. If they already have one, consider getting a backup or keeping one in multiple locations (home, work, car).
Simon Downes, MD, PhD 