Weed stays in your system anywhere from 3 days to 90 days, depending on the type of drug test and how often you use it. A one-time smoker will typically test clean on a urine test within 3 to 4 days, while a daily user may test positive for 10 to 21 days. The single biggest factor is your frequency of use, but body fat, metabolism, and the type of test all play a role.
Detection Windows by Test Type
Different drug tests look for THC or its byproducts in different parts of the body, and each has its own detection window.
Urine tests are by far the most common. The standard screening looks for THC metabolites at a cutoff of 50 nanograms per milliliter (ng/mL). At that threshold, here’s what to expect:
- Single use: detectable for up to 3 days
- Moderate use (about 4 times a week): 5 to 7 days
- Daily use: 10 to 15 days
- Heavy daily use (multiple times a day): up to 30 days
Some labs use a lower cutoff of 20 ng/mL, which extends these windows. At that stricter threshold, a single use could show up for about 7 days, and chronic use could be detected for up to 21 days. A review published in Drug Court Review concluded that even at the lower cutoff, it would be uncommon for anyone to test positive beyond 21 days after their last session.
Blood tests have a much shorter window. THC is detectable in blood for 24 to 48 hours in most people. Heavy, chronic users are the exception: THC can linger in their blood for up to 25 days. Blood tests are less common for employment screening and more often used in roadside testing or medical settings, where the goal is to detect recent or active impairment.
Saliva tests detect THC for roughly 24 to 72 hours. These are becoming more popular for workplace testing because they’re easy to administer and focus on very recent use. Cleveland Clinic estimates detection at up to 24 hours, though some sources extend that to 72 hours for heavier users.
Hair tests have the longest detection window: up to 90 days. Head hair grows about half an inch per month, so a standard 1.5-inch sample captures approximately three months of history. Hair testing is less common and typically reserved for situations requiring a longer look-back period.
Why THC Lingers Longer Than Other Drugs
Most recreational drugs are water-soluble, meaning your body flushes them relatively quickly. THC is different. It dissolves in fat, and after you use cannabis, your body converts THC into metabolites that get stored in fat cells throughout your body. This is the main reason weed has such a long detection window compared to substances like alcohol or cocaine.
When you use cannabis occasionally, your body clears the stored metabolites within a few days. About 70% to 90% of a single THC dose is excreted within 3 to 5 days. But with repeated use, THC and its byproducts build up in fat tissue faster than your body can release and eliminate them. The active compound has a plasma half-life of about 1.5 to 2 hours, but the inactive metabolite that drug tests actually look for has a half-life of 120 to 144 hours (5 to 6 days). That slow breakdown is what keeps chronic users testing positive for weeks.
Factors That Speed Up or Slow Down Clearance
How Often and How Much You Use
Frequency of use is the dominant variable. Someone who smoked once at a party is dealing with a fundamentally different timeline than someone who uses multiple times a day. Heavy daily users accumulate so much THC in their fat stores that even after quitting completely, it can take weeks for levels to drop below the testing threshold.
Body Fat Percentage
Since THC binds to fat molecules, people with a higher body fat percentage have more storage space for THC metabolites. A leaner person with a faster metabolism will generally clear THC more quickly than someone with a higher BMI, even if they used the same amount.
Metabolism and Genetics
Your individual metabolic rate, shaped by genetics, age, and overall health, affects how quickly your liver processes THC. Some people are naturally “fast metabolizers” who break down THC efficiently, while others are “slow metabolizers.” Metabolism also tends to slow with age, which can extend clearance times for older adults.
Method of Consumption
Edibles are processed through the digestive system and liver, which changes how THC is absorbed and metabolized compared to smoking or vaping. While the available research on detection windows focuses primarily on smoked cannabis, edibles generally produce a more prolonged release of THC metabolites because absorption is slower and more extended.
Why Exercise and Water Won’t Save You
It’s tempting to think you can sweat or flush THC out of your system before a test. The reality is more complicated. Exercise does release stored THC from fat cells into the bloodstream through a process called lipolysis, but this can actually backfire. One study found that frequent aerobic exercise elevated THC blood levels temporarily by freeing it from fat stores. Over time, regular exercise may support elimination, but working out right before a test could spike your levels.
Drinking large amounts of water dilutes your urine, which can lower the concentration of THC metabolites in a sample. But this doesn’t speed up actual clearance from your body, since the metabolites are stored in fat, not floating in water. Labs are also trained to flag overly diluted samples, which can result in a retest. Detox drinks work on the same principle: they’re typically loaded with diuretics that temporarily dilute urine without doing anything to your underlying metabolite levels.
What Drug Tests Actually Measure
An important distinction: most drug tests don’t measure active THC, the compound that causes impairment. They measure an inactive metabolite called THC-COOH, which your liver produces after breaking down THC. This metabolite has no psychoactive effect. It simply indicates that cannabis was used at some point in the past. This is why you can test positive days or weeks after your last use, long after any impairment has worn off.
The standard federal urine screening uses an initial cutoff of 50 ng/mL. If that comes back positive, a confirmatory test is run at a lower cutoff of 15 ng/mL to verify the result. The initial screen casts a wide net, and the confirmation test narrows it down. Knowing which cutoff your test uses matters, because the difference between 50 ng/mL and 20 ng/mL can mean several extra days of detection.
For blood tests, the distinction between active THC and the inactive metabolite is more relevant. Active THC drops below detectable levels within hours for occasional users, but the inactive metabolite can persist much longer. This is why blood tests are sometimes used to assess recent impairment, while urine tests are better suited for detecting use over a longer period.