Before taking Doxepin tell your doctor or chemist if you are allergic to it; or if you have other allergies. Some conditions may become worse when this drug is suddenly stopped. A very serious allergic reaction rarely occurs. Do not drive, use machinery, or do anything that needs alertness or clear vision until you can do it safely. If you have missed your dose, take it as soon as you remember. This drug may make you dizzy or drowsy or blur your vision. Limit alcoholic beverages. To prevent constipation, maintain a diet adequate in fiber, drink plenty of water, and exercise.