Why Do We Reach for Benadryl (Diphenhydramine)?
I often get asked about Benadryl (diphenhydramine). A vast majority of the time when someone has a rash or thinks they are having an allergic reaction, the knee-jerk response is to reach for diphenhydramine. Even if someone is taking cetirizine (Zyrtec) or fexofenadine (Allegra) and they have breakthrough symptoms, they reach for Benadryl. I surveyed ER doctors and asked what made them give diphenhydramine versus another non-sedating antihistamine and they largely provided two answers:
- The belief that it worked faster and better
- Cost, as it is cheaper
Is There Data to Support Benadryl’s Reputation?
I then asked if they had any data to support the idea that it worked “faster and better,” and none of them could provide any. The reason they could not give any is because I do not believe it exists as I have yet to see it. Why do we continue to reach for it? Largely because of myth. What does the data say?
What Does the Research Show?
I published a paper and looked at how quickly diphenhydramine (both oral and an intramuscular injection) suppressed histamine in a skin test as compared to oral fexofenadine. Bottom line: there WAS NO STATISTICALLY SIGNIFICANT difference. Oral fexofenadine performed just as well as even an injection of diphenhydramine. The only difference was fexofenadine lasted longer! (See figures)
Myths of Diphenhydramine
4 Myths of Diphenhydramine
- It works faster than other non-sedating antihistamines
- It works better than other non-sedating antihistamines
- It should be used in more severe allergic reactions
- It should be used in food allergies
Facts About Diphenhydramine
4 Facts of Diphenhydramine
- It can impair measures of driving performance more than alcohol in experimental conditions
- It increases risk of injury at work more than hypnotics or narcotics
- Impairment is independent of feeling tired
- Diphenhydramine should NEVER replace the use of epinephrine in an acute and severe allergic reaction
The Take-Home Message
In a severe, acute allergic reaction, epinephrine is the drug of choice. Most fatalities arise with food allergy when there is a delay in epinephrine being given or it is not administered at all. Many fear epinephrine, but the medication is not the problem—it is the remedy. The problem of the severe allergic reaction is already occurring (and often quickly). Many will delay or not give epinephrine because of the stigma of going to the emergency room. In a severe reaction, that will likely be happening anyway. Giving epinephrine early in anaphylaxis can prevent further complications or catastrophe.
Jones DH, Romero FA, Casale TB. Time-dependent inhibition of histamine-induced cutaneous responses by oral fexofenadine and oral and intramuscular diphenhydramine. Annals of Allergy, Asthma, and Immunology. 2008;100:452-456.
.png)