How long does Marijuana last in the system? Marijuana is the most commonly used illicit drug. The length it lasts in your system is different than other drugs. If the test that is completed is a urine test, it can show up to 30 days after usage depending on the factors listed above. Saliva tests have a time limit of 72 hours after usage and blood tests can detect marijuana up to 4 hours after use. Hair follicle tests can detect marijuana up to 90 days before the test.