Weed, or marijuana, stays in the system for varying lengths depending on frequency of use, test type, metabolism, body fat, and other factors. Typically:

• In urine tests, THC metabolites can be detected for about 1 to 3 days after a single use, 5 to 7 days with moderate use, 10 to 15 days if used daily, and 30 days or more for heavy use.
• Blood tests detect THC for up to 12 hours, maybe longer with heavy use.
• Saliva tests detect weed for up to 24 hours.
• Hair tests can show THC use for up to 90 days.
• THC is stored in fat cells and metabolized slowly, which extends detection in heavy users.

The effects of the drug last a few hours, but metabolites stay in the body weeks after the high has worn off. There is no reliable method to speed up the elimination process beyond metabolic and lifestyle factors.