Marijuana can stay in your system anywhere from 24 hours to 90 days, depending on the type of drug test. For the most common test, a urine screening, a single use is typically detectable for 3 to 4 days, while regular use can be detected for up to 21 days. The biggest factors that determine your detection window are how often you use, what kind of test you’re facing, and the cutoff level the lab applies.
Detection Windows by Test Type
Not all drug tests measure the same thing or look back the same distance in time. Here’s what to expect from each type.
Urine Tests
Urine testing is by far the most common method used for employment and legal screenings. These tests don’t look for THC itself but for a byproduct your body creates as it breaks THC down. Most standard urine panels use a cutoff of 50 ng/mL, meaning the test only flags positive if that byproduct is present above that concentration.
At the standard 50 ng/mL cutoff, a one-time or occasional user will generally test clean within 3 to 4 days. For someone who uses regularly, the window extends but is unlikely to exceed 10 days after the last session. Some labs use a more sensitive 20 ng/mL cutoff, which stretches the window further: up to 7 days for a single use and up to 21 days for chronic use. Even at that lower threshold, detection beyond 21 days is uncommon.
These numbers may be shorter or longer depending on your body composition, metabolism, and hydration level, but they represent well-studied averages. The THC byproduct that urine tests detect has an average half-life of about 2 days, according to research from Johns Hopkins, meaning your body reduces its concentration by roughly half every 48 hours once you stop using.
Saliva Tests
Oral fluid tests have the shortest detection window. Cannabis is typically detectable in saliva for up to 24 hours after use. These tests are increasingly popular for roadside checks and some workplace screenings because they’re quick, hard to tamper with, and better at identifying very recent use rather than use from days or weeks ago.
Blood Tests
Blood tests detect active THC rather than its byproducts, so they primarily reflect recent use. THC enters the bloodstream almost immediately after smoking and peaks within minutes. For occasional users, THC drops below detectable levels in blood within a few hours to a couple of days. Frequent users may test positive for several days longer because THC accumulates in fat tissue and slowly re-enters the bloodstream over time. Blood tests are less common for employment screenings and more often used in clinical or legal contexts like DUI investigations.
Hair Tests
Hair follicle tests have the longest look-back window: up to 90 days. As THC byproducts circulate through your bloodstream, trace amounts get deposited into the hair follicle and become locked into the hair shaft as it grows. Labs typically collect a 1.5-inch sample from the scalp, which represents about three months of growth. Hair tests cannot pinpoint the exact date of use since hair growth rates vary between people, but they’re effective at identifying patterns of use over that three-month period. These tests are less common for standard pre-employment screenings but are used in some industries, court-ordered testing, and federal positions.
Why Frequency of Use Matters Most
THC is fat-soluble, which is the key reason it lingers in your body far longer than most other substances. When you consume cannabis, your body stores THC in fat cells throughout your tissues. A single use deposits a small amount that clears relatively quickly. But with repeated use, THC accumulates in those fat stores faster than your body can eliminate it, creating a reservoir that slowly releases back into your bloodstream and eventually into your urine over days or weeks.
This is why a person who smoked once at a party faces a fundamentally different timeline than someone who uses daily. The daily user has built up significant THC stores in their fat tissue, and even after stopping completely, those stores take time to deplete. Body fat percentage plays a role here too. Someone with more body fat can retain THC byproducts longer than a leaner person, all else being equal. Physical activity, metabolism rate, and hydration also influence how quickly your body processes and excretes them.
Edibles vs. Smoking
The method of consumption changes how THC enters and moves through your body, which can affect detection. When you smoke or vape, THC hits your bloodstream through the lungs almost instantly, peaks quickly, and starts declining right away. With edibles, THC is absorbed through the digestive tract and processed by the liver first, which means it enters the bloodstream more slowly and produces a prolonged release of THC byproducts.
In practical terms, edibles can extend the window during which your body is actively producing detectable byproducts compared to the same dose smoked. The overall detection window in urine still depends primarily on frequency of use, but edibles may push the timeline slightly longer for equivalent amounts of THC because of that slower, more sustained metabolic process.
What Can Cause a False Positive
Standard urine drug screens use a method called immunoassay, which is fast and inexpensive but not perfectly specific. Certain medications and substances can trigger a false positive for cannabinoids. These include some proton pump inhibitors (commonly taken for acid reflux), the anti-seizure medication lamotrigine, the HIV medication efavirenz, and the prescription cannabinoid dronabinol.
Ibuprofen and naproxen are frequently cited as potential culprits, though it’s worth noting that the immunoassay formulations responsible for ibuprofen false positives were corrected over 20 years ago. Modern tests are less likely to have this issue, but older references still list it. If you receive a positive result you believe is wrong, a confirmation test using a more precise method can distinguish between actual THC byproducts and cross-reacting substances. Most formal testing programs automatically send positive screens for this confirmation step before reporting a final result.
Federal and Workplace Testing Rules
Despite shifting state laws around recreational and medical marijuana, federal drug testing requirements have not changed. In December 2025, an executive order directed the Department of Justice to reschedule marijuana from Schedule I to Schedule III, but that process is not yet complete. Until it is, marijuana remains a Schedule I substance under federal testing rules.
For anyone in a safety-sensitive transportation role governed by the Department of Transportation, marijuana use is still prohibited and tested for regardless of state legality. The DOT explicitly stated that its drug testing regulations, along with the procedures labs and medical review officers follow, will remain unchanged until rescheduling is finalized. Private employers outside of federal oversight set their own policies, and some have dropped THC from their panels in states where cannabis is legal, but this varies widely by company and industry.
Quick Reference by User Type
- One-time or occasional use: Urine positive for 3 to 4 days (standard cutoff) or up to 7 days (sensitive cutoff). Saliva up to 24 hours. Blood up to 1 to 2 days.
- Regular use (several times per week): Urine positive for up to 10 days at standard cutoff, potentially longer at sensitive cutoff.
- Daily or heavy use: Urine positive for up to 21 days at sensitive cutoff. Blood potentially positive for several days. Hair positive for up to 90 days.
These ranges assume you’ve stopped using entirely. Continued use, even occasional, resets the clock and adds to the THC stored in your fat tissue, extending the window further.