NyQuil typically takes about 30 minutes to start working after it is taken. This can vary depending on factors such as dosage and individual metabolism, with some people feeling effects as soon as 15 minutes. The ingredient doxylamine succinate in NyQuil causes drowsiness, which can last 6 to 8 hours, making it suitable for nighttime use to help with sleep while relieving cold and flu symptoms like coughing, sneezing, and body aches.
