Benadryl (diphenhydramine) typically stays in your system anywhere from about 4 to 60 hours, depending on various factors such as age, metabolism, dosage, liver and kidney health, and frequency of use.

• The half-life of diphenhydramine-the time it takes for half the drug to be eliminated-ranges from approximately 2.4 to 9.3 hours, averaging around 4.3 hours in healthy young adults

• Based on this half-life, it can take roughly 13 to 49 hours for Benadryl to be fully cleared from the body

• Some sources note that while the primary effects of Benadryl usually wear off within 4 to 6 hours, the drug itself can remain detectable in the system for up to 48 to 60 hours

• Drug tests can detect diphenhydramine in urine for up to 4 days, and in blood and saliva for 3 to 4 days after the last dose

Factors that influence how long Benadryl stays in your system include:

• Age: Older adults and children metabolize it more slowly, extending its presence

• Metabolism and hydration: Faster metabolism and good hydration help clear the drug quicker

• Dosage and frequency: Higher doses and frequent use prolong elimination time

• Liver and kidney function: Impaired organ function slows metabolism and clearance

• Body composition: Higher body fat can retain the drug longer since diphenhydramine is lipophilic

In summary, while you may stop feeling Benadryl’s effects after 4 to 6 hours, it can remain in your system for 1 to 3 days or longer depending on individual factors