How Long After Zyrtec Can You Take Benadryl?
In our latest question and answer, the pharmacist discusses how long after taking Zyrtec you can safely take Benadryl.
I’m having an allergic reaction from going through musty files from last night for 2.5 hours. My nose wouldn't stop running all day today. I took a dissolvable Zyrtec at 5:30 PM, can I now take a Benadryl tonight at 11:30 PM?
Oct 05, 2021- Both Zyrtec and Benadryl are antihistamines that work the same way, so taking them together increases the risk of side effects like drowsiness, dry mouth, dizziness, and constipation.
- You should ideally wait 24 hours after taking Zyrtec before taking Benadryl, though your doctor may recommend taking them closer together in certain situations like a mild allergic reaction.
- Taking both medications together should only be done intermittently as needed, not on a daily basis.
Answer
Taking Zyrtec (cetirizine) and Benadryl (diphenhydramine) at the same time should only be done with caution due to the risk of increased adverse events.
If you are looking to take Benadryl after a dose of Zyrtec, you ideally want to wait 24 hours (as that is the length of time Zyrtec works), but there are situations where your doctor may recommend taking it soon.
Potential Side Effects Of Taking Both Together
Both Benadryl and Zyrtec are antihistamines and they work the same way. Taking them together greatly increases the risk of side effects such as:
- Drowsiness
- Dry mouth
- Dizziness
- Constipation
- Dry eyes
Can You Take Benadryl After Zyrtec?
Zyrtec is a "second-generation" antihistamine, with a duration of action of around 24 hours while Benadryl is a "first-generation" antihistamine, and lasts only four to six hours per dose.
Since Zyrtec lasts around 24 hours, to best avoid additive side effects, Benadryl should ideally be taken 24 hours after your last Zyrtec dose.
One situation where taking both within a 24 window may be recommended, however, is if you are experiencing a mild allergic reaction.
Although data from studies are mixed, Benadryl may be slightly better at stemming the symptoms of an allergic reaction (e.g. inflammation, itching) than newer, second-generation antihistamines, like Zyrtec and Allegra.
It doesn't seem as though Benadryl is markedly better than the newer antihistamines in this regard, but some people do tend to respond better to it.
While you may be at an increased risk of certain side effects (such as drowsiness) from taking Benadryl and Zyrtec close together, they typically are mild in severity, and the benefits of taking Benadryl to lessen the effects of an allergic reaction could outweigh the risk of the mild side effects in most people.
In addition, your doctor may recommend you take Benadryl for allergy symptoms that are severe, and don't seem to lessen after taking your Zyrtec.
In general, they just shouldn't be taken together on a daily basis, only as needed intermittently.
Lastly, it's not uncommon to use Benadryl to help sleep at night, even if you are taking a daily antihistamine. Again, it shouldn't be a daily occurrence but is generally considered safe for most when done intermittently.
Final Words
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References & sources
Glossary — Terms in This Answer
- Antihistamines
- Medications that block histamine, a chemical in the body that causes allergy symptoms like itching and inflammation.
- Adverse events
- Unwanted or harmful side effects that occur from taking a medication.
- Additive side effects
- Additional or increased side effects that occur when two medications with similar actions are taken together.
- Duration of action
- The length of time a medication continues to work in your body.
- Second-generation antihistamine
- A newer type of antihistamine medication designed to cause less drowsiness than older versions.
- First-generation antihistamine
- An older type of antihistamine that is more likely to cause drowsiness as a side effect.
- Allergic reaction
- An immune system response to a substance that causes symptoms like itching, swelling, or inflammation.
- Inflammation
- Swelling and irritation in the body, often caused by allergies or injury.
Dr. Brian Staiger, PharmD
Doctor of Pharmacy, board certified clinical pharmacist (BCPS), American Herbalist Guild, Medication Therapy Management certified
Brian Staiger, PharmD, BCPS, is a licensed pharmacist with more than 13 years of experience across retail pharmacy, clinical pharmacy, medication safety, pharmacy program development, and healthcare administration. He is the founder of HelloPharmacist.com, where he helps patients...
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