Im due in 6weeks how long will it take to get a negative at birth for marijuana use? Please let Doctor: & medical team know about your use. Single use of marijuana should be out of your urine in 1 to 7 days. Regular use of marijuana – should be out of urine in 7 to 100 days. Single use marijuana can be detected 12 to 24 hours in blood. Regular use marijuana can be detected for 2 to 7 days in blood. Marijuana regular use detected in hair for months.