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Does Benadryl cause heart palpitations?

Benadryl (diphenhydramine) is a commonly used over-the-counter antihistamine medication that is used to treat allergies, insomnia, motion sickness, and more. It works by blocking the effects of histamine, a chemical released by the body during an allergic reaction. While Benadryl is generally considered safe when used as directed, some people do report experiencing heart palpitations after taking it.

What are heart palpitations?

Heart palpitations are feelings that your heart is pounding, fluttering, skipping a beat, or beating too hard or too fast. They can feel like your heart is throbbing or racing. Palpitations can occur occasionally in healthy people and may not indicate any underlying medical condition. However, frequent or prolonged palpitations may potentially be a sign of an arrhythmia or other heart issue.

Can Benadryl cause heart palpitations?

Benadryl can sometimes cause heart palpitations as a side effect. This is because Benadryl has anticholinergic properties that can affect the heart. Specifically, Benadryl blocks acetylcholine, a neurotransmitter that helps regulate heart rate. When levels of acetylcholine are lowered, it can disrupt the heart’s normal rhythm and lead to palpitations in some people.

In addition, Benadryl causes drowsiness by crossing the blood-brain barrier and blocking histamine receptors in the brain. This antihistamine effect can also spread to other areas and block cholinergic receptors in the autonomic nervous system that help control heart rate. Suppressing these signals that keep the heart rhythm steady can potentially trigger palpitations.

Who may be at risk for Benadryl-related palpitations?

While anyone can experience heart palpitations after taking Benadryl, some people may be at increased risk, including:

  • Older adults – increased sensitivity to medications and decreased heart rate variability
  • People taking other anticholinergic drugs – additive effects
  • People with heart conditions like arrhythmia or congestive heart failure
  • People taking stimulants like caffeine or ADHD medications – can exacerbate effects
  • People with electrolyte imbalances like low potassium or magnesium

What is the incidence of palpitations with Benadryl use?

The exact incidence of palpitations associated specifically with Benadryl is unknown. However, some research provides estimates:

  • One study found that about 3% of adults taking diphenhydramine (Benadryl) experienced palpitations.
  • Another study found clinically significant arrhythmias in 7-8% of hospitalized patients taking Benadryl.
  • Up to 15% of older adults were found to have new-onset atrial fibrillation associated with anticholinergic drug use like Benadryl.

So while palpitations appear to be an uncommon side effect, they seem to occur in a low single-digit percentage of Benadryl users based on available data.

Are Benadryl-induced palpitations dangerous?

In most cases, heart palpitations caused by Benadryl are notdangerous or life-threatening. They tend to resolve on their own once the antihistamine effects wear off. However, palpitations can sometimes indicate underlying arrhythmias like atrial fibrillation, which can increase the risk of stroke if left untreated. Prolonged episodes of palpitations should be evaluated by a doctor.

How long do Benadryl-related palpitations last?

For most people, Benadryl-related palpitations are temporary and go away once the medication is metabolized and cleared from the body. The duration can vary depending on the person and dosage taken:

  • With a standard dose of Benadryl (25-50 mg), palpitations may last anywhere from a few minutes up to several hours.
  • In overdose situations with very high doses, palpitations and arrhythmias can persist for 12 hours or longer.
  • For older adults or those very sensitive to anticholinergics, palpitations may last 4-6 hours.

If palpitations continue beyond 12 hours or do not go away after the Benadryl should have cleared your system, medical evaluation is recommended.

Will Benadryl always cause palpitations?

No, Benadryl does not reliably or consistently produce heart palpitations in all users. Most people can take Benadryl without experiencing any heart-related side effects. However, some people are prone to palpitations with Benadryl use. Risk factors like old age, heart conditions, electrolyte imbalance, and concurrent medications can increase likelihood.

Can you prevent Benadryl-induced palpitations?

There are some steps you can take to potentially prevent or reduce your risk of palpitations with Benadryl:

  • Use the lowest effective dose.
  • Avoid taking other anticholinergic medications concurrently.
  • Stay well hydrated and get sufficient magnesium and potassium.
  • Limit or avoid caffeinated drinks when taking Benadryl.
  • Take Benadryl earlier in the day since drowsiness can exacerbate effects.
  • Avoid alcohol when using Benadryl.
  • Discuss risk factors and alternatives with your doctor.

However, there is no foolproof way to guarantee Benadryl will not cause palpitations as people can respond differently.

What should you do if Benadryl causes palpitations?

If you experience heart palpitations after taking Benadryl, here are some tips:

  • Try to stay calm and take slow breaths until it passes.
  • Check your pulse and monitor symptoms.
  • Reduce physical activity and avoid driving until resolved.
  • Drink water and get fresh air if dizzy or lightheaded.
  • Call doctor if palpitations last >12 hours or are accompanied by chest pain.
  • For severe reactions, seek emergency medical care right away.

Be sure to follow up with your doctor for evaluation, especially if you have an underlying heart condition or experienced prolonged palpitations.

Are there alternatives to Benadryl less likely to cause palpitations?

There are some alternatives to Benadryl that have less anticholinergic activity in the heart and thus may be less likely to cause palpitations:

  • Second-generation antihistamines like cetirizine (Zyrtec), fexofenadine (Allegra), or loratadine (Claritin)
  • Intranasal corticosteroid sprays like fluticasone (Flonase) for allergies
  • Other OTC sleep aids like melatonin or doxylamine succinate (Unisom)
  • Prescription non-sedating antihistamines like levocetirizine (Xyzal)

However, it is still possible for any antihistamine to cause palpitations in some people. Talk to your doctor about the best options for your symptoms and medical history.

Key Points

  • Benadryl can cause temporary heart palpitations in some people due to its anticholinergic effects.
  • Older adults, those with heart conditions, and people on multiple medications have highest risk.
  • Palpitations from standard doses of Benadryl usually last under 6 hours.
  • While uncomfortable, Benadryl-related palpitations are not usually dangerous.
  • Using the lowest effective dose and staying hydrated may help reduce risk.
  • Alternative antihistamines like cetirizine have less effect on the heart.
  • See a doctor if palpitations last >12 hours or you have chest pain.

The bottom line

Benadryl can cause temporary heart palpitations as a side effect in some people. However, serious complications are rare. Using alternative medications, lowering your dose, and avoiding interactions can help minimize your risk. Speak to your healthcare provider if you have any concerns about taking Benadryl.

Here is a summary table of the key points:

Key Question Answer
Can Benadryl cause palpitations? Yes, due to its anticholinergic effects
Who is most at risk? Older adults, those with heart conditions, people on multiple meds
How long do they last? Usually under 6 hours with normal doses
Are they dangerous? Rarely, but can indicate arrhythmias
Can you prevent them? Lower dose, stay hydrated, avoid interactions
What are some alternatives? Cetirizine (Zyrtec), loratadine (Claritin), etc.


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