Does Benadryl Make Your Heart Race?

In our latest question and answer, the pharmacist discusses whether or not Benadryl, an over the counter antihistamine, can cause your heart to race.

Question

I took Benadryl and feel like it has opposite effects on me. My heart pounds. Does Benadryl make your heart race?

Asked by Sammi On Jun 30, 2018

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Jun 30, 2018

Yes, Benadryl can increase your heart rate (i.e. "make your heart race"), even at recommended doses. This is because Benadryl, a sedating "first-generation" antihistamine, has strong anticholinergic effects.


Common anticholinergic side effects include:

  • Feeling hot or overheated
  • Constipation
  • Dry eyes
  • Dry mouth
  • Tachycardia (i.e. increased heart rate)
  • Confusion
  • Sedation
  • Dry skin
  • Flushing


It should be noted that cardiac side effects of Benadryl, such as increased heart rate, aren't all that common. Nevertheless, if your heart rate has increased after dosing with Benadryl, or you are having palpitations, it may be the culprit.


Benadryl Causing Excitation 

In addition, Benadryl has been reported to cause "paradoxical excitation" in individuals, and appears to be more common in children as well as in cases of an overdose according to the prescribing information for the drug. Symptoms of this include:

  • Restlessness
  • Agitation
  • Insomnia
  • Muscle spasms
  • Increased heart rate


The side effect of "excitation" is noted as paradoxical as Benadryl is more commonly associated with a feeling of sedation, which is why it is used as a sleep aid. 


Lastly, it appears certain individuals are more susceptible to the "excitation" side effects of Benaryl than others, a subject we discussed in this article: Why Does Benadryl Make You Anxious? The theory is that some individuals have genetic variations that increase the metabolism of Benadryl, increasing concentrations of an excitatory metabolite.


Summary

  • Benadryl has been documented cases of increased heart rate.
  • An increased heart rate from Benadryl is most commonly seen in children and in cases of an overdose.
  • Certain individuals may have a genetic variation that increases concentrations of a Benadryl metabolite that causes excitation.

About the Pharmacist

Dr. Brian Staiger Pharm.D

Dr. Brian Staiger is a licensed pharmacist in New York State and the founder of PharmacistAnswers.com. He graduated from the University At Buffalo with a Doctor of Pharmacy degree in 2010. He has been featured in numerous publications including the Huffington Post as well as a variety of health and pharmacy-related blogs. Please feel free to reach out to him directly if you have any inquiries or want to connect! He's answered thousands of medication and pharmacy-related questions and he's ready to answer yours! Brian.Staiger@PharmacistAnswers.com Office: 716-389-3076

About Benadryl (Diphenhydramine)

Benadryl (diphenhydramine) is a first generation, sedating antihistamine (H1-blocker) of the ethanolamine class. It is available in oral, topical, and parenteral product forms. Benadryl is well known to cause significant sedation in most individuals and is commonly used in night-time sleep aids. Benadryl also has potent "drying" effects in most patients, which is why is causes dry mouth, dry eyes and constipation. The onset of action of Benadryl is around 15-30 minutes after taking by mouth, with peak effects occurring 1 to 3 hours later. The duration of action is around 4 to 6 hours, with this being prolonged in the elderly and in those with liver disease.

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