Why Does NyQuil Make You Sleepy?

In our latest question and answer, the pharmacist discusses why NyQuil makes you tired.


I am curious as to how exactly NyQuil makes you tired. Is it a specific ingredient?

Asked by James On Mar 23, 2018

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Mar 23, 2018

NyQuilNyQuil is a multi-drug product used in the treatment of cold and flu symptoms. The ingredient in NyQuil that causes you to be sleepy is doxylamine, a sedating first-generation antihistamine similar to Benadryl. NyQuil also contains 10% alcohol by volume, which likely adds to the sedative effects.


NyQuil contains the following drugs:

  • Acetaminophen: Pain and fever reducer
  • Dextromethorphan: Cough suppressant to help control a cough
  • Doxylamine: Sedating antihistamine to aid in sleep and help with runny nose and sneezing

NyQuil is used in the treatment of cold and flu symptoms. It is the doxylamine in the NyQuil Cold & Flu Nighttime Relief that causes the drowsiness and can make you feel tired. Acetaminophen and Dextromethorphan are also found in NyQuil, but these drugs typically do not cause the drowsiness or tired feeling like doxylamine does.


Doxylamine is the ingredient in NyQuil that causes drowsiness or sleepiness. Doxylamine is a first generation antihistamine, similar to Benadryl. First generation antihistamines are noted for their relatively short duration of action (~4-8 hours) and their sedative effects. Besides drowsiness, other common side effects include:

  • Dizziness
  • Constipation
  • Dry mouth and throat
  • Blurred vision
  • Urinary retention


  • The ingredients in NyQuil that make you tired are doxylamine and the alcohol content.

About the Pharmacist

Ms. Jennifer Hauder RPh

Jennifer Hauder is a registered pharmacist in the state of Illinois. She has over 10 years experience as a pharmacist in the retail and pharmacy benefit managers (PBM) settings. She became a pharmacist due to her interest in healthcare and the opportunity to help others with their healthcare needs. When not working, she enjoys spending time with her husband, three children and two black labs Lucky and Charms.

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