How long does drowsiness generally last after a benadryl (diphenhydramine)?

Four to six hours. The half life of Benadryl (diphenhydramine) is about four to six hours and usually the sedation will wear off within that time frame. As one continues to use it often a certain amount of tolerance develops and less sedation is appreciated. Studies have shown that its effect on brain function still continues despite less sedation.

Related Questions

Why does Benadryl (diphenhydramine) causes drowsiness?

Enters the brain. The molecular structure of benedryl allows it to enter the brain where it can interfere with the chemicals that transfer messages between brain cells. In most people it causes drowsiness, in some it will cause the opposite. Newer antihistamines like loritadine & fexofinadine have molecular structures that prevent entry into the brain, so they don't make you drousy. Read more...

Benadryl (diphenhydramine) has effect on me -- drowsiness?

Common effect. Benedryl is one of the most common products in over the counter sleep aids. It works quickly & well for allergies, but if you read the small print on most bottles it warns you of this effect. Occasionally some people get the opposite effect & get hyper on it, but that is far less common than the sedation. It actually enters your brain & messes with the neuro-transmitters. Read more...