In the vast majority of individuals, it is safe to take Allegra (fexofenadine) in the same day as NyQuil. However, they generally should not be taken at the same time. At the very least, they should be separated from one another by at least four to six hours to decrease the possibility of excess sedation and drowsiness as Allegra is an antihistamine and NyQuil contains an antihistamine.


NyQuil - Allegra Interaction

Allegra (fexofenadine) is a "second generation" antihistamine and has a duration of action of around 24 hours. Most second-generation antihistamines do not cause drowsiness or sedation, including Allegra. While Allegra doesn't cause drowsiness on its own, it can still increase the risk of sedation when used with other sedating medications.


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

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


Doxylamine, like Allegra, is an antihistamine but is classified as a "first generation" antihistamine. First generation antihistamines are characterized by their short duration of action (~4 to 6 hours) and their sedative effects. While doxylamine is effective for the treatment of allergy symptoms, it is most often used in over the counter products as a sleep aid.


The concern with using NyQuil and Allegra at the same time is the potential for additive antihistamine side effects from each, which potentially includes:

  • Drowsiness
  • Constipation
  • Dry mouth
  • Dry eyes
  • Sedation


Generally speaking, Allegra should not be taken at the same time as NyQuil due to the additive sedative effects. However, if you take Allegra in the morning for your allergy symptoms and you tolerate it well, you can certainly take NyQuil safely in the evening to help with cough/cold symptoms and for problems falling asleep.