DayQuil is a combination ingredient product that contains the following active ingredients:

  • Acetaminophen 325 mg (per 15 mL)
  • Dextromethorphan HBr 10 mg (per 15 mL)
  • Phenylephrine HCl 5 mg (per 15 mL)

Each ingredient in DayQuil has an onset of action of 15-30 minutes.

How Fast DayQuil Works

DayQuil will begin to work 15 to 30 minutes after taking a dose.

As DayQuil contains 3 different active ingredients, how quickly you will feel the of effects each will vary, although only slightly.

  • Acetaminophen, an analgesic, has an onset of action of 15-20 minutes, but peak effects occur within 30 to 60 minutes.

  • Dextromethorphan, a cough suppressant, is rapidly absorbed from the GI tract and begins to work in 15-30 minutes.

  • Phenylephrine, a nasal decongestant, has an onset of action 15-30 minute after taking a dose by mouth but peak effects occur approximately 1 to 2 hours after administration.

DayQuil Severe, which contains an additional ingredient (guaifenesin), also has an onset of action of around 15 to 30 minutes.

The manufacturer website for DayQuil, in their 'FAQ' section, also lists the onset of action as 30 minutes:

Q: How long does it take for DayQuil to work?
A: This depends on many factors but it usually takes 30 minutes for DayQuil to start working.

Answer Summary

DayQuil generally starts working about 15-30 minutes after taking a dose.

  1. Tylenol Dosing Guide. Tylenol Professional
  2. Pharmacokinetics of dextromethorphan and metabolites in humans: influence of the CYP2D6 phenotype and quinidine inhibition. PubMed
  3. Pharmacokinetics, safety, and cardiovascular tolerability of phenylephrine HCl 10, 20, and 30 mg after a single oral administration in healthy volunteers. PubMed