DayQuil will begin working within 30 minutes after taking a dose by mouth. Below, we go into more detail about each medication contained in DayQuil and discuss how long it usually takes for each to being exerting effects.


DayQuil Onset Of Action

DayQuil contains the following medications:

  • Acetaminophen (analgesic)
  • Dextromethorphan (cough suppressant)
  • Phenylephrine (decongestant)


Acetaminophen, the active ingredient in Tylenol, is a pain reliever and fever reducer. It begins to work quickly after taking a dose by mouth, within 15 to 30 minutes. Peak effects however, occur within 30 to 60 minutes. 


Dextromethorphan is a cough suppressant that is rapidly absorbed from the GI tract, with antitussive activity appearing within 15 to 30 minutes.


Phenylephrine is a nasal decongestant. Like acetaminophen and dextromethorphan, the onset of action will occur in 15 to 30 minutes. Peak concentrations are achieved approximately 1 to 2 hours after administration.


As you can see, all of the ingredients in DayQuil begin to work within 15-30 minutes. The duration of action of DayQuil is approximately 4 to 6 hours. The maximum daily amount of DayQuil recommended per day is 4 doses.