Almost everyone suffers from trouble sleeping at one time or another, reports the Harvard Medical School HealthBeat. Insomnia—the inability to sleep—isn’t a single disorder itself, but rather a general symptom like fever or pain.

People with insomnia may be plagued by trouble falling asleep, unwelcome awakenings during the night, and fitful sleep. They may experience daytime drowsiness, yet still be unable to nap, and are often anxious and irritable or forgetful and unable to concentrate.

Nearly half of insomnia stems from underlying psychological or emotional issues. Stressful events, mild depression, or an anxiety disorder can keep people awake at night. When the underlying cause is properly treated, insomnia usually improves. If not, additional strategies to help promote sleep may be needed.

Over-the-counter sleep aids

Walk into any drugstore, and you’ll find a bewildering variety of over-the-counter sleep products. And people are buying them. One small survey of people ages 60 and over found that more than a quarter had taken nonprescription sleeping aids in the preceding year—and that one in 12 did so daily.

Standard nonprescription sleeping pills

Despite the many brands, nearly all of them—whether a tablet, capsule, or gel cap—contains an antihistamine as its primary active ingredient. Most over-the-counter sleep aids—including Nytol, Sominex, and others—contain 25 to 50 milligrams (mg) of the antihistamine diphenhydramine. A few, such as Unisom SleepTabs, contain 25 mg of doxylamine, another antihistamine. Others—including Aspirin-Free Anacin PM and Extra Strength Tylenol PM—combine antihistamines with 500 mg of the pain reliever acetaminophen.

Such antihistamines have a sedating effect and are generally safe. But they can cause nausea and, more rarely, fast or irregular heartbeat, blurred vision, or heightened sensitivity to sunlight. Complications are generally more common in children and people over age 60. 

Alcohol heightens the effect of these medications, which can also interact with some drugs. If you take nonprescription sleeping pills, be sure to ask your physician about the possibility of interactions with other medications.

Sleep experts generally advise against using these medications, not only because of side effects but also because these products are often ineffective in relieving sleep problems. Furthermore, there is no information about the safety of taking such medications over the long term.

To read more about ways to improve your sleep as well as the pros and cons of using prescription sleep aids, dietary supplements, herbal remedies, or mechanical devices, purchase Improving Sleep - A guide to a good night’s rest by Harvard Medical School.