For a single use, weed is typically detectable in urine for 3 to 4 days. For regular users, that window extends to about 10 days, and daily heavy users can test positive for up to 21 days after their last use. But the exact timeline depends on the type of test, how often you use, and your body composition.
Urine Test Detection Windows
Urine testing is by far the most common method, especially for employment screening. The standard cutoff used in federal workplace testing is 50 ng/mL for an initial screen, with a confirmatory test at 15 ng/mL. Most private employers use that same 50 ng/mL threshold.
At the standard 50 ng/mL cutoff, here’s what to expect:
- One-time or occasional use: 3 to 4 days
- Moderate use (a few times per week): 5 to 7 days
- Daily or near-daily use: up to 10 days
Some labs and testing programs use a lower cutoff of 20 ng/mL, which catches smaller amounts of metabolites. At that threshold, a single use could show up for about 7 days, and chronic daily use could be detectable for up to 21 days. A review published in Drug Court Review found it would be “uncommon” for anyone to test positive beyond 21 days, even at the lower cutoff. The widely circulated idea that heavy users can test positive for 30, 60, or 90 days is not well supported by controlled evidence.
Blood, Saliva, and Hair Tests
Blood tests have the shortest detection window. THC is only measurable in blood for a few hours after use, making this test useful mainly for detecting very recent consumption, like in roadside impairment checks.
Saliva tests detect THC for roughly 24 hours, though some evidence suggests the window can stretch to about 30 hours. Federal oral fluid testing uses a cutoff of 4 ng/mL for the initial screen and 2 ng/mL for confirmation. Saliva testing is becoming more common in workplace programs because it’s harder to tamper with than urine.
Hair follicle tests cover the longest period: up to 3 months. As THC metabolites circulate in your blood, they get deposited into hair follicles and remain locked into the hair shaft as it grows. Labs typically collect a 1.5-inch sample from the scalp, which represents roughly 90 days of growth. The tradeoff is that hair tests can’t pinpoint when you used, only that you did at some point during that window. They’re also less reliable for detecting a single, isolated use.
Why THC Lingers Longer Than Other Drugs
Most recreational drugs dissolve in water, get processed by your liver and kidneys, and leave your body within a day or two. THC works differently. It dissolves in fat, not water, which means your body stores it in fat cells throughout your tissues. Over time, those fat cells slowly release THC and its metabolites back into your bloodstream, where they eventually get filtered out through urine.
This is why frequency of use matters so much. If you smoke once, there’s a small amount stored in fat that clears quickly. If you use daily for weeks or months, THC accumulates across a much larger reservoir of fat tissue, and it takes longer for your body to work through that backlog.
What Speeds Up or Slows Down Clearance
Your body fat percentage is the single biggest factor beyond usage frequency. People with more body fat have more storage capacity for THC, which means a longer detection window. People with less body fat and a faster metabolism will generally clear it sooner. Hydration, age, and overall metabolic rate also play smaller roles.
Exercise creates a counterintuitive wrinkle. Because physical activity burns fat, it can actually release stored THC back into your bloodstream. Researchers at the University of Sydney recruited 14 daily cannabis users and had them ride an exercise bike hard for 35 minutes. Every participant showed increased THC blood levels after the workout, and in some cases the spike was high enough to trigger a positive test result, despite not having used cannabis since the night before. If you have a test coming up, intense exercise in the days right before could temporarily raise your metabolite levels rather than lower them.
Drinking large amounts of water right before a test can dilute your urine, which may bring metabolite concentrations below the cutoff. However, labs check for dilution. If your sample is flagged as too dilute, you’ll likely be asked to retest, and a second dilute result is often treated as a positive.
Can Secondhand Smoke Make You Fail?
It’s possible, but only under extreme conditions. Research from UCLA Health found that people exposed to marijuana smoke for three hours in a well-ventilated space had THC levels well below the threshold for a positive test. However, people exposed to high-potency marijuana smoke for an hour in an unventilated, enclosed room absorbed enough THC to fail a standard drug screen and showed impaired motor skills. Casual exposure at a party or walking past someone smoking outdoors won’t put you at risk.
Federal Workplace Testing Still Includes Marijuana
Even as marijuana laws change at the state level, federal workplace drug testing has not changed. The Department of Transportation still tests safety-sensitive workers (truck drivers, pilots, train operators, pipeline workers) for marijuana under the same rules. A December 2025 executive order directed the rescheduling of marijuana from Schedule I to Schedule III, but until that process is complete, DOT regulations remain in effect and a positive marijuana result is still a violation. Many private employers in states with legal marijuana have dropped THC from their panels, but you should know your employer’s specific policy before assuming your test won’t include it.