Question: how long does diphenhydramine make you drowsy?
Answer: If you're taking diphenhydramine for short-term sleep problems, it will start to make you feel drowsy around 20 to 30 minutes after you take it. For coughs and colds, your symptoms will normally start to improve within 20 minutes. The medicine should work for around 4 to 6 hours. How long can I take it for?