How Long Does Weed Stay in Your System?

Sources: urine windows from Moeller et al., Mayo Clinic Proceedings; blood from StatPearls and Bergamaschi et al.; saliva from Niedbala et al.; hair from Taylor et al.. Every window is an average from studies, not a promise about any one person.

Urine is the specimen most workplaces use, and frequency of use is the biggest driver of how long it stays positive. A clinical review in Mayo Clinic Proceedings gives these approximate windows at standard screening cutoffs:

Mayo Clinic Laboratories publishes a similar table (up to 3, 5, 10, and 30 days respectively) and notes the actual time "depends on dose, frequency of use, and individual metabolism." StatPearls puts infrequent users at 1–3 days (up to 5) and chronic users at 10–30 days or longer, and a separate StatPearls chapter notes cannabinoids can be detectable in urine for up to 3 months after heavy chronic use.

In a controlled single-dose study, urine first turned positive about 4–6 hours after smoking and the last positive specimen came an average of 42–58 hours later, with a maximum of 72 hours.

The high from smoked cannabis fades within hours, but the body keeps clearing what it absorbed for much longer. THC is fat-soluble: it is stored in fatty tissue and released slowly, and the liver converts it to THC-COOH, the metabolite urine tests detect. Mayo Clinic Laboratories describes THC-COOH as inactive and very lipid soluble.

The clinical review lists the factors that change the window: route of use, dose, product potency, frequency of use, body mass, and individual metabolism. Frequency matters most, because regular use builds up a reservoir in fat that keeps releasing metabolite after you stop. That is also why two people who used the same amount on the same day can get different results.

A drug test does not report "any THC at all." It reports whether a sample is above a cutoff concentration. Under the federal workplace guidelines, a urine screen is positive at 50 ng/mL of THC-COOH and must be confirmed at 15 ng/mL by a second, more specific test. Oral fluid uses 4 ng/mL of THC to screen and 2 ng/mL to confirm. Some labs use a lower 20 ng/mL urine screen, which catches use for longer.

Screening is usually done by immunoassay, and a presumptive positive is confirmed with gas or liquid chromatography–mass spectrometry. If you are being tested, the cutoff the lab uses is one of the few details worth asking about.

A positive cannabinoid test confirms exposure, not impairment. Because THC-COOH can linger for days or weeks, a urine positive cannot say when you last used or whether you were high at the time of the test. Blood and saliva are closer to recent use, but even blood can stay positive for weeks in chronic daily users who have stopped.

Legal products are not exempt. CBD products that contain small amounts of THC can produce a positive urine test; see CBD and drug tests. For the employment side (when a positive can cost you a job, and when state law steps in) see our cannabis laws hub.