Weed can stay in your system anywhere from 1 day to 90 days, depending on the type of drug test and how often you use it. The biggest factors are which biological sample is being tested (urine, blood, saliva, or hair) and your frequency of use. A single smoke session clears far faster than daily use over weeks or months.
Why THC Lingers Longer Than Other Drugs
Most recreational drugs dissolve in water and flush out relatively quickly. THC is different. It’s fat-soluble, meaning your body pulls it out of the bloodstream and stores it in fat tissue. Over time, that stored THC slowly leaks back into circulation and gets broken down by the liver into metabolites, primarily one called THC-COOH. Drug tests usually look for THC-COOH rather than THC itself, because the metabolite sticks around much longer.
For someone who uses cannabis infrequently, THC has a half-life of about 1.3 days. For frequent users, that half-life stretches to 5 to 13 days. This means it takes roughly twice as long for your body to clear half the THC each cycle, and several cycles to eliminate it fully. The delayed clearance in heavy users is caused by THC accumulating in fat tissue and releasing slowly over time.
Urine Tests: The Most Common Screening
Urine testing is the standard for most workplace and pre-employment drug screens. What matters here is the cutoff level the lab uses. Federal workplace testing programs follow guidelines set by SAMHSA, which recommend a screening cutoff of 50 ng/mL and a confirmatory cutoff of 15 ng/mL.
At the standard 50 ng/mL cutoff, a single use is typically detectable for only 1 to 2 days. Drop to a 20 ng/mL cutoff (used by some employers and courts) and that window extends to 1 to 6 days depending on the dose. More sensitive lab methods like GC-MS can detect metabolites for roughly twice as long as standard immunoassay screens.
These numbers apply to occasional or one-time users. If you use cannabis regularly, detection windows expand significantly. General estimates by usage pattern:
- Single or occasional use (once a week or less): 3 to 7 days
- Moderate use (a few times per week): 7 to 21 days
- Daily or heavy use: 30 days or longer, with some chronic users testing positive beyond 45 days
The wide ranges exist because individual biology plays a large role. Two people with identical usage patterns can test differently based on metabolism, hydration, and body composition.
Blood Tests: A Much Shorter Window
Blood tests detect active THC rather than stored metabolites, so the detection window is considerably shorter. After smoking, THC peaks in the blood within about 10 minutes, then drops sharply. For most people, THC falls below detectable levels in whole blood within 3 to 6 hours of a single session.
In a controlled study where participants smoked one cannabis cigarette, THC was undetectable in whole blood for all but one participant by 22 hours post-use. That one outlier still had measurable THC, likely due to individual metabolic variation. The metabolite THC-COOH, however, was still detectable in extended blood samples at 22 hours for all participants, with concentrations varying widely from person to person.
Blood testing is less common for employment screening but is used in DUI investigations and some clinical settings, where the goal is to identify very recent use.
Saliva Tests: Hours, Not Days
Oral fluid testing has the shortest reliable detection window. Cannabis is generally detectable in saliva from about 1 hour after use up to 48 hours, though most positive results fall within the first 24 hours. This makes saliva tests useful for identifying same-day or very recent use, which is why they’re increasingly used in roadside testing.
One nuance with edibles: when you eat cannabis, THC residue coats the inside of your mouth during consumption. This means an oral fluid test can pick up THC almost immediately after eating an edible, but the signal reflects topical residue in the mouth rather than what’s circulating in your blood. The peak concentration in saliva is lower with edibles than with smoking, and the metabolite THC-COOH appears on a delayed timeline.
Hair Tests: Up to 90 Days
Hair follicle tests have the longest detection window of any standard method, reaching back approximately 90 days. As THC metabolites circulate in your blood, small amounts get incorporated into the hair shaft as it grows. A standard hair test uses 1.5 inches of hair measured from the scalp, and since hair grows roughly half an inch per month, that sample covers about three months of history.
Hair tests are less common due to cost and are typically reserved for situations where employers or courts want a longer-term picture of drug use rather than a snapshot of recent activity. They are not effective at detecting a single or very recent use, since it takes about a week for new hair growth containing the metabolite to emerge from the scalp.
Edibles vs. Smoking: Does It Matter?
The method of consumption changes how quickly THC enters and leaves your bloodstream, which can affect detection timing. When you smoke or vape cannabis, blood THC peaks within minutes and drops to baseline within 3 to 6 hours. Edibles are slower: THC peaks in the blood 2 to 3 hours after eating, and levels don’t return to baseline until 6 to 20 hours post-dose.
This slower absorption means edibles keep THC circulating in your blood for longer per session. For a blood or saliva test taken the morning after use, an edible consumed the previous evening could be more likely to show a positive result than a joint smoked at the same time. For urine testing over a period of days, though, total THC exposure matters more than the method of delivery.
Body Fat, Exercise, and Other Variables
Because THC is stored in fat, your body composition directly influences how long it stays detectable. People with higher body fat percentages retain more THC and release it more slowly. The correlation works in both directions: leaner individuals tend to clear THC faster.
Exercise adds an interesting wrinkle. A study of regular cannabis users found that a session of moderate exercise caused a small but statistically significant spike in blood THC levels. The effect was strongest in participants with higher BMI, supporting the theory that physical activity mobilizes THC stored in fat cells. In practical terms, this means exercising shortly before a blood test could temporarily raise your THC levels. Fasting alone, at least over a short period, did not produce the same effect.
Other factors that influence clearance speed include your metabolic rate, hydration level, genetics affecting liver enzyme activity, and the potency of the cannabis used. These variables are why no online calculator can give you a guaranteed timeline.
Can Secondhand Smoke Cause a Positive Test?
Under normal social circumstances, secondhand cannabis smoke is very unlikely to trigger a positive drug test. In a controlled experiment, non-smokers were exposed to cannabis smoke in enclosed spaces. At the standard federal cutoff of 50 ng/mL, only a single presumptive positive occurred across all participants and sessions, a positivity rate of 0.4%. Even at the lower 20 ng/mL cutoff, positives only appeared within 1 to 4 hours of exposure and resolved within 22 hours.
The key detail: the conditions that produced any positive results involved extreme exposure in an unventilated room. Sitting next to someone smoking a joint at a party or briefly passing through a smoky area is not enough to put you at realistic risk. If you do find yourself in a heavily smoke-filled, sealed room, any detectable metabolites would clear within a day.