Does dayquil keep you awake? DayQuil is an over-the-counter medication used to alleviate symptoms of cold and flu, such as congestion, cough, and fever. It contains ingredients like acetaminophen, dextromethorphan, and phenylephrine, which can cause drowsiness in some individuals, while others may not experience this effect. It's essential to read the label and understand how your body reacts to the medication. While DayQuil generally doesn't cause drowsiness, it's crucial to monitor your response to it, especially if you need to stay alert during the day.