NyQuil typically remains in your system for several hours to a day depending on several factors Generally the effects of NyQuil and symptom relief can be felt for about 4 to 6 hours but traces of the medication may linger longer
One of NyQuil’s active ingredients doxylamine has a half-life of 10 hours and it can take up to 2 days to be completely eliminated from the body[6] For individuals with liver conditions or those taking other medications NyQuil might stay in the system longer and have prolonged effects