When you have chronic persistent insomnia which is affecting your day-to-day activities. As a rule, I try to stay away from them and instead try to get to the bottom of what is going on with my life--stress caused by work or personal life, not getting enough exercise... but I when I haven't had more than 3 hours sleep for several days in a row, I will take one (usually not more as your body can build up a tolerance to any drug and sleeping pills do have addictive qualities). The use of sleeping medications as well as how many and how often you take them is something you need to discuss with your doctor. I've also found it helpful to ask the pharmacist I go to to review any side effects with me and also to check to be sure there will be no harmful reactions to combining them with any other meds, vitamins and herbs I may be on.