NyQuil is a combination ingredient product that is used to treat the symptoms of colds and the flu. How long the effects of NyQuil last varies by individual but generally lasts around four to six hours per dose.


Per the manufacturing labeling for NyQuil, it is important not to exceed 4 doses in a 24 hour period. Based on the duration of action of NyQuil, each dose should be separated by at least 6 hours.


Time To Wait Between NyQuil Doses

NyQuil contains the following ingredients:

  • Acetaminophen 650 mg (Pain reliever/fever reducer)
  • Dextromethorphan HBr 30 mg (Cough suppressant)
  • Doxylamine succinate 12.5 mg (Antihistamine)


Each ingredient in NyQuil has a duration of action of around 4 to 6 hours, although the sedative effects (which come from the sedating antihistamine doxylamine) have been known to last up to 8 hours in certain individuals. It is important to not take an additional dose of NyQuil if you are still feeling the sedating effects from the product. 


However, if the effects of your last dose of NyQuil have worn off, you are safe to take another dose as long as 6 hours has past since your last dose. Waiting 6 hours between doses will ensure that you do not take more than the recommended maximum 4 daily doses.