Taking Zyrtec With NyQuil

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In most cases, it is safe to take Zyrtec (cetirizine) the same day as taking NyQuil.

However, they generally should not be taken at the same time, or, at least should be separated from one another by at least a few hours to lessen the possibility of excess sedation and drowsiness.

More Info On NyQuil - Zyrtec Interaction

Zyrtec (cetirizine) is a "second generation" antihistamine that is an effective all-day (i.e. 24 hour) allergy medication.

While most second-generation antihistamines do not cause drowsiness or sedation (e.g. Claritin), Zyrtec is not considered non-drowsy. In fact, clinical studies for Zyrtec have reported that about 13% of users will experience sedation.

NyQuil is a combination ingredient cough/cold medication and contains the following active ingredients:

• Acetaminophen (analgesic)
• Dextromethorphan (cough suppressant)
• Doxylamine (sedating antihistamine)

Doxylamine, like Zyrtec, is an antihistamine, although it is considered "first generation". First-generation antihistamines are characterized by their relatively short duration of action (~4 to 6 hours) and by the sedation they cause. 

While doxylamine is effective for the treatment of allergy symptoms, it is most often used in over-the-counter products as a sleep aid due to the sedation is causes.

The concern with using NyQuil and Zyrtec at the same time is the potential for additive side effects from each, which could include:

• Drowsiness
• Dry mouth
• Dry eyes
• Sedation

This interaction, for most people, wouldn't be considered too serious, but it is a drug interaction nonetheless, so is important to be aware of.

Final Words

Overall, Zyrtec should not be taken at the same time as NyQuil due to the additive sedative effects, as described in the section above.

However, if you take Zyrtec in the morning and tolerate it well, you can certainly take NyQuil in the evening with no ill effects.