Do not drive, use machinery, or do anything that needs alertness or clear vision until you can do it safely. To prevent constipation, maintain a diet adequate in fiber, drink plenty of water, and exercise. Read the Medication Guide provided by your pharmacist before you start taking doxepin and each time you get a refill. It works by affecting the balance of certain natural chemicals (neurotransmitters) in the brain. Drowsiness, dizziness, dry mouth, blurred vision, constipation, or trouble urinating may occur. Alcohol or marijuana can make you more dizzy or drowsy. We provide only general information about medications which does not cover all directions, possible drug integrations, or precautions. To help you remember, take it at the same time(s) each day.