The January 2011 issue of Bottom Line/Health has an article called “Dirty Drugs” about popular drugs with bad side effects. It is based on an interview with an assistant professor of medicine at Harvard named James Rudolph. It contains the following:
Insomnia. Most OTC drugs taken for insomnia, including the allergy medicine Benadryl and sleep aid Sominex, contain diphenhydramine. It can cause constipation, difficulty concentrating, urinary retention, and trouble with eye focus — and stays active in the body for 12 to 18 hours, which can cause next-day grogginess.
My advice. Avoid taking diphenhydramine for insomnia.
Better. Practice good sleep habits. Examples: Go to bed at a reasonable hour, and maintain the same schedule every night. Exercise regularly but not within two hours of bedtime — it will make falling asleep more difficult. Take a warm bath before bed to help you relax.
I agree, insomnia drugs are bad news. But the “better” advice could be a hundred years old.