Testing cutoff concentrations for benzodiazepine are at 200 ng/mL. So how long do benzos stay in the body? Benzodiazepine can be detected up to 30 days in urine although chronic use (1+ years) can be detected 4–6 weeks after last dose in urine. Benzos can also be detected in serum and plasma for 12 hours to 2 days after last dose.