A single dose of Diphenhydramine hydrochloride, commonly known as Benadryl, is active in the body for between four and six hours on average. The drug is almost completely excreted from the body within 24 hours, as explai... More »

When used for male hormone replacement, various types of testosterone therapy can last in the body from 24 hours up to 22 days. Testosterone gels last for 24 hours, patches last for 24 hours, tablets last for 12 hours, a... More »

Provigil stays in a person's system for several days after it is taken. The drug is used to treat sleep disorders in adults according to the Provigil website. More »

An oral dose of Benadryl reaches peak blood concentrations 2 to 3 hours after consumption, and the effects usually last for 4 to 6 hours, reports the National Highway Traffic Safety Administration. WebMD suggests taking ... More »

The allergy medication Benadryl typically stays in the system for four to six hours. Most products instruct users to take the stated dosage every four to six hours as needed, while not exceeding six doses in a single day... More »

The lethal dose of diphenhydramine, the generic name of Benadryl, varies significantly from person to person because of differences in weight and metabolism. There have been cases of people experiencing overdose symptoms... More »

A side effect of Benadryl is that it causes drowsiness, which can make people fall asleep. Numerous over-the-counter sleep aids contain antihistamines such as diphenhydramine and doxylamine succinate because of their pot... More »