How long does cannabis stay in your system for drug testing purposes?

Detection windows vary dramatically by test type, frequency of use, and individual metabolism. Urine (most common): THC-COOH (inactive metabolite) is detectable for 3–4 days in occasional users, 10–15 days in moderate users, and 30+ days (sometimes 90+ days) in daily heavy users. THC-COOH is lipophilic and accumulates in fat tissue, explaining prolonged detection in heavy users. Blood: THC detectable for 3–4 hours after acute use; in heavy users, detectable for 1–7 days. Blood testing reflects recent use more accurately than urine. Saliva: THC detectable for 1–3 days; used for roadside impairment testing. Hair: THC metabolites detectable for 90 days (reflects 3 months of use). Important caveats: (1) Urine testing detects past use, not current impairment. (2) Secondhand smoke exposure rarely causes positive tests at standard cutoffs. (3) CBD products with trace THC (<0.3%) can cause positive urine tests in heavy CBD users. (4) Workplace drug testing policies vary by state and employer.