Debunking the Myths About Benadryl (Diphenhydramine)

Why People Reach for Benadryl

I often get asked about Benadryl (diphenhydramine). A vast majority of the time when someone has a rash or think they are having an allergic reaction, the knee-jerk response is to reach for the 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 anti-histamine and they largely provided two answers:

The belief that it worked faster and better

Cost, as it is cheaper

What the Data Actually Says

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?

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 is 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)

4 Myths of Diphenhydramine

• It works faster than other non-sedating anti-histamines
• It works better than other non-sedating anti-histamines
• It should be used in more severe allergic reactions
• It should be used in food allergies

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

The take-home messages are 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 furthering complications or catastrophe.

Reference

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.

‍