The Real Reason Nyquil Makes You Sleepy

Nyquil might be one of the first medications you reach for when you have a cold and are looking to get a good night's sleep. The popular over-the-counter brand has been around for years, and the company has developed several nighttime and daytime formulas to treat a variety of cold and flu symptoms that include coughing, a sore throat, fever, and headaches. 

The active ingredients listed in Nyquil are acetaminophen, dextromethorphan HBr, and doxylamine succinate. Acetaminophen acts as a pain reliever and fever reducer, while dextromethorphan HBr is used to suppress coughing. Meanwhile, doxylamine succinate is an antihistamine, a common ingredient in allergy medications that blocks the natural histamine your body makes to help eliminate a runny nose and watery eyes (per WebMD). Other ingredients include potassium and sodium. 

So, if Nyquil is made to treat symptoms associated with a cold or flu, why do you feel sleepy after taking it? 

While Nyquil is not specifically marketed as a sleep aid, it does contain ingredients that might make your drowsy, which allow you to get the rest you need when you're fighting a cold. 

One side effect of dextromethorphan is drowsiness. The histamine doxylamine can also make you feel sleepy, according to Healthline. However, there is another ingredient in Nyquil that causes drowsiness, and that is alcohol. Believe it or not, some Nyquil products contain as much as 10% alcohol, per Vicks. Most wines contain anywhere from 11% to 13% alcohol, per Real Simple. 

That being said, alcohol is not listed as one of the active ingredients in Nyquil. Instead, it is used to dissolve the other ingredients in the recipe, according to Medical News Today. Because Nyquil does contain alcohol, Vicks suggests not drinking any other type of alcohol with it, and to use caution when driving or using machinery after taking it.