Marijuana can stay in your system anywhere from a few hours to 90 days, depending on the type of test and how often you use it. The single biggest factor is frequency of use: a one-time smoke session clears from urine in 3 to 4 days, while daily use can keep you testing positive for up to 21 days.
Why THC Lingers Longer Than Other Drugs
Most drugs dissolve in water, get processed by your liver, and leave your body within a day or two. THC works differently. It’s highly fat-soluble, meaning your body rapidly absorbs it into fat tissue after you inhale or ingest it. From there, it slowly leaks back into your bloodstream over days or weeks as your body metabolizes that fat.
This is why the “high” wears off in a few hours but the chemical evidence sticks around much longer. Your liver converts active THC into an inactive byproduct called THC-COOH, and that byproduct is what most drug tests actually look for. In occasional users, the half-life of THC in blood is 1 to 3 days. In chronic users, it stretches to 5 to 13 days, with some heavy users showing measurable levels for four full weeks after their last use.
Detection Windows by Test Type
Urine Tests
Urine screening is by far the most common method for employment and legal testing. The standard cutoff used in workplace testing is 50 ng/mL, set by federal guidelines. How long you’ll test positive at that threshold depends almost entirely on how often you use:
- Single or occasional use: 3 to 4 days at the standard 50 ng/mL cutoff. Even at a more sensitive 20 ng/mL cutoff, a single session wouldn’t be expected to show up beyond 7 days.
- Regular use (several times per week): Up to 10 days at the standard cutoff.
- Daily or heavy use: Up to 21 days, even at the more sensitive 20 ng/mL threshold. At the standard cutoff, it would be unlikely to exceed 10 days.
The widely cited “30 days” figure is largely a myth for most people. Research published in the Drug Court Review found that even chronic users are unlikely to test positive beyond 21 days at any cutoff level. That said, individual variation exists, and people with higher body fat percentages may retain THC metabolites somewhat longer because there’s simply more fat tissue storing the compound.
Saliva Tests
Oral fluid tests detect THC itself (not the metabolite), which means they’re measuring more recent use. Cannabis is typically detectable in saliva for up to 24 hours, though some evidence suggests detection can stretch to about 30 hours after smoking. This makes saliva tests better at identifying very recent use rather than something from last week. They’re increasingly used in roadside testing and some workplace programs.
Blood Tests
Blood tests detect active THC circulating in your bloodstream and have the shortest detection window of any method. THC levels in blood spike within minutes of smoking, then drop sharply. The initial elimination half-life is roughly 1 to 2 hours, meaning blood concentrations fall quickly once you stop inhaling. Blood tests are mostly used in medical settings or DUI investigations where the question is whether someone is currently impaired, not whether they used cannabis last week.
Hair Tests
Hair testing has the longest detection window: up to 90 days. As THC metabolites circulate in your bloodstream, they get incorporated into the hair shaft as it grows. Since head hair grows at an average rate of half an inch per month, a standard 1.5-inch hair sample covers roughly three months of history. Hair tests are less common for routine employment screening but are sometimes used when employers want a longer usage history. They’re poor at detecting a single, isolated use because the amount of metabolite deposited in the hair from one session may be too small to trigger a positive result.
Factors That Affect Your Timeline
Frequency of use matters most, but several other factors influence how quickly your body clears THC:
Body fat percentage. Because THC is stored in fat tissue, people with more body fat tend to retain metabolites longer. Two people who smoke the same amount on the same day can have noticeably different detection windows based on body composition alone.
Metabolism and activity level. A faster metabolism processes and eliminates THC-COOH more quickly. However, exercise can actually work against you in the short term. Researchers at the University of Sydney found that exercise, which burns fat for energy, releases stored THC back into the bloodstream. In some study participants, post-exercise THC levels rose high enough to trigger a positive test result. So working out to “flush” THC before a test may temporarily raise your levels rather than lower them.
Potency and dose. Higher-THC products deposit more metabolites into your system. A single hit from a low-potency joint creates a smaller metabolite load than a dab of concentrate, and your body clears that smaller load faster.
Method of consumption. Edibles are processed through the digestive system and liver before reaching the bloodstream, which produces higher concentrations of the THC-COOH metabolite compared to smoking the same dose. This can extend the urine detection window slightly.
What About Detox Drinks and Cleanses
Products marketed as THC detoxes or cleanses have no reliable scientific backing. Most work by diluting your urine with excess fluid, which can lower the concentration of metabolites below the test cutoff temporarily. But testing labs check for dilution. If your urine sample is too dilute (measured by its creatinine level and specific gravity), the result is flagged as inconclusive and you’ll typically be asked to retest.
Fasting doesn’t appear to help either. The same University of Sydney research found that 12 hours of fasting had no effect on THC blood levels, unlike exercise, which did cause a measurable spike. There is no shortcut that reliably accelerates the elimination of THC from fat stores. The only consistently effective approach is time.
Quick Reference by User Type
- One-time user, urine test: 3 to 4 days
- Occasional user (a few times per month), urine test: Up to 7 days
- Regular user (several times per week), urine test: Up to 10 days
- Daily user, urine test: Up to 21 days
- Saliva test, any user: Up to 24 to 30 hours
- Blood test, any user: A few hours
- Hair test, any user: Up to 90 days
These windows assume standard testing cutoffs. Some employers or legal systems use lower thresholds, which can extend detection times by several days for urine tests. If you know a test is coming and aren’t sure which cutoff applies, the more conservative estimates (using the 20 ng/mL numbers) give you a safer picture of your actual window.