Benadryl typically stays in the body for about 2 to 3 days, though its noticeable effects last only 4 to 6 hours. Its half-life is roughly 4 to 9 hours, meaning most of the drug is eliminated within a day or two in healthy adults. Factors like age, liver function, dosage, and metabolism can extend clearance time. In urine tests, traces may occasionally be detectable for up to 48–72 hours.