More over-the-counter sleep aids are purchased than any other OTC drug, and 25% of Americans take some type of medication every year to help them sleep. Popular OTC brands include Benadryl, Nytol, Sominex, Tylenol PM, Advil PM and Nyquil. Their main ingredient is an antihistamine named diphenhydramine and in some case (Nyquil), alcohol.

Common Brand Names     Generic Name of Main Ingredient

Benadryl                            diphenhydramine

Not all sleep medications are prescription. FDA has approved over-the-counter (OTC) medications for use up to two weeks to help relieve occasional sleepiness in people ages 12 and older. "If you continue to have sleeping problems beyond two weeks, you should see a doctor," says Marina Chang, R.Ph., pharmacist and team leader in FDA's Division of Nonprescription Regulation Development.

OTC sleep aids are non-habit-forming and do not present the risk of allergic reactions and complex sleep-related behaviors that are known to occur with sedative-hypnotic drugs.

But just because they're available over-the-counter doesn't mean they don't have side effects, says Chang. "They don't have the same level of precision as the prescription drugs. They don't completely stop working after 8 hours—many people feel drowsy for longer than 8 hours after taking them."

Chang advises reading the product label and exercising caution when taking OTC sleep aids until you learn how they will affect you. "They affect people differently," she says. "They are not for everybody."