Can taking a benedryl affect a drug test?

It depends,,: It depends on what you're being tested for and how much benedryl you took. Apparently it may cause a false positive result for Methadone in some urine drug screens using competitive binding immunoassays, and if too much is taken, it can cause blurry vision, photophobia, heart failure, and death, but a lot has to be taken. Otherwise, there should not be much of a problem. Good luck.