Usually how long can weed stay in someones system?

Depends on 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. Single use might not be picked up in hair.