How long does weed stay in your system? It depends on the test and on how often you use cannabis. A standard urine test can pick up a single use for up to about three days, while chronic, heavy use can show up for a month or more. Blood and saliva tests mostly catch recent use, and hair tests can reach back about three months. These are typical ranges, not promises, because bodies and tests vary. Here's the chart, what moves the numbers and what a result can and can't tell you.
How long does weed stay in your system? The detection chart
Every drug test has its own detection window. In practice, the test you take decides how long marijuana stays detectable. A SAMHSA guide for clinicians calls its own figures approximate, and they shift with the dose, your habits, your body and the lab's cutoff.
| Test | What it looks for | Occasional use | Frequent or heavy use |
|---|---|---|---|
| Urine | THC-COOH, an inactive by-product of THC | Up to about 3 days | Up to about 10 days with heavy use; 30 days or more with chronic, heavy use |
| Blood | THC itself | Hours | Days; at least a week in some heavy users |
| Saliva | THC left in the mouth | Hours to a day or two | Up to about 3 days in some heavy users |
| Hair | THC-COOH trapped in the hair shaft | Often not detected | Up to about 3 months |
For urine, the SAMHSA guide breaks the window down further:
- Single use: up to 3 days
- Moderate use: up to 4 days
- Heavy use: up to 10 days
- Chronic, heavy use: 30 to 36 days
THC vs. THC-COOH: what a test is really measuring
THC is the compound behind cannabis's effects. Your liver breaks it down into THC metabolites, and the main one labs look for in urine is THC-COOH. It's inactive, meaning it doesn't produce a high, but it lingers.
The reason is fat. THC dissolves easily in fat, so some of it is stored in fatty tissue and slowly seeps back into the bloodstream at very low levels. From there it's broken down and passed in urine. That slow release is why regular use leaves such a long tail.
Tests don't flag every trace of THC-COOH. They use cutoffs. Under federal workplace guidelines, a urine sample screens positive at 50 nanograms per milliliter, and a positive screen then goes to a second, more precise lab test with a cutoff of 15. Some clinical tests screen at 20, which catches smaller amounts and stretches the window.
Urine, blood, saliva and hair tests compared
Urine tests
A urine screen targets THC-COOH rather than THC, which is why it can pick up use from days or even weeks before. How long THC stays in urine depends mostly on how often you use, as the chart shows.
Blood tests: how long does weed stay in your blood?
Blood tests look for THC itself, which drops quickly after occasional use, so the window is usually hours. Heavy, long-term use is a different story. In an Australian study of 21 dependent users in residential detox, some still had detectable THC in their blood after 7 days without cannabis.
Saliva tests
Saliva tests pick up THC left in the mouth after smoking, vaping or eating cannabis, so they mainly reflect recent use. In the same Australian study, some heavy users' saliva still tested positive for THC up to 78 hours after they entered detox.
Hair tests
A hair test for marijuana looks back much further. Hair grows about a centimeter a month, and labs usually test a segment covering about three months. Metabolites take roughly 7 to 10 days to appear in hair, so it can't show very recent use. Cannabis metabolites also bind to hair less readily than many other drugs, which makes hair a poor tool for catching occasional use.
What makes the detection window longer or shorter
The SAMHSA guide lists the factors that matter most:
- How often you use. This is the big one. A single use and daily use produce very different timelines.
- How much THC you take. More THC, or more potent products, means more to clear.
- Body fat. Because THC is stored in fat, people with more body fat may hold on to it longer.
- Metabolism. How quickly your body processes THC varies from person to person.
- Hydration at test time. How dilute your urine is affects the reading.
- The test itself. A lower cutoff catches smaller amounts for longer.
That's why no chart can promise an exact day. Two people with similar habits can get different results from the same test.
Frequent use and long detection windows
With daily, long-term use, more THC ends up stored in fat, and it keeps seeping out for weeks after you stop. The SAMHSA guide puts urine detection at 30 to 36 days for chronic, heavy use. In the Australian detox study, some participants' urine still held more than 1,000 nanograms per milliliter of THC-COOH more than five days after their last use. That's 20 times the standard screening cutoff.
A short break doesn't reset things. If you're stepping away from cannabis to bring your tolerance down, our guide to T-breaks explains how to plan one. Just don't count on a few days off to clear a test.
Edibles vs. smoking: which shows up longer?
If you're wondering how long edibles stay in your system, the short answer is that switching to them won't shorten anything. In a Johns Hopkins study published in 2022, 21 infrequent users ate THC brownies in some sessions and vaped cannabis in others. At both active dose levels, peak metabolite levels in urine were higher after eating (10 or 25 mg of THC) than after vaping (5 or 20 mg). Under federal workplace cutoffs, urine tested positive after 98% of the edible sessions and 60% of the vaping sessions.
The study only tracked the first 8 hours after each dose, so it doesn't settle how many extra days edibles might add. It does show that eating cannabis is no way around a test. How much THC you take and how often you use still matter most. Learn more about how edibles work.
Testing positive after the effects fade
A positive test shows that cannabis was used at some point. It doesn't show when, or whether someone is impaired right now. Urine tests measure an inactive by-product that can linger well after the high is gone, sometimes for weeks, so a heavy user can test positive while completely sober.
The reverse holds too: a negative result isn't a green light. Tests measure chemicals, not how you feel or how well you can drive. If you feel the effects, don't drive. Michigan's adult-use law doesn't cover driving or operating a vehicle while under the influence.
CBD products and drug tests
Standard drug tests look for THC's by-product, not CBD. In a 2020 study, healthy adults took 100 mg of pure CBD, swallowed or vaped, and none of their urine samples crossed the federal lab-test cutoff. Only one of 218 samples even screened positive at the most sensitive screening level.
The catch is THC. When the same volunteers vaped CBD-dominant cannabis that also contained 3.7 mg of THC, several samples tested positive. Products sold as CBD can carry THC, so read the label for THC content if you're tested.
Myths: detox drinks, sweating it out and niacin
Detox drinks. Products that promise to cleanse urine mostly have you drink large amounts of fluid, which waters the sample down. Labs routinely check whether a sample has been diluted. A sample that looks too dilute is reported that way, which can mean a retest. Time clears THC metabolites, not a drink.
Sweating it out. THC is stored in fat and released slowly, and a hard workout or a sauna session doesn't put you in charge of that schedule. There's no good evidence that sweating shortens a detection window.
Niacin. Niacin, a B vitamin, is promoted as a way to flush THC. There's no good evidence it works. Emergency doctors have reported serious reactions, including liver damage, in people who took it to try to pass a drug test.
Secondhand smoke. Being around people who smoke usually doesn't produce a positive at the standard 50 ng/mL workplace cutoff, according to the SAMHSA guide. Extreme exposure, such as sitting in a closed car with people smoking, can push levels past a lower 20 ng/mL clinical cutoff.
What to weigh before buying if you're tested
If your job or another program tests for cannabis, think these through before you buy anything:
- Your workplace policy. Legal isn't the same as allowed at work. Michigan's adult-use law doesn't make employers permit cannabis, and they can still enforce drug policies, discipline workers or decline to hire someone who violates them.
- Product type. Edibles aren't a workaround, as the Johns Hopkins study showed.
- CBD labels. A product sold as CBD can still contain THC, so read the THC line.
- Timing and frequency. Even occasional use can show up for days, and regular use for weeks. If your job has a no-cannabis policy, the only dependable plan is not to use.
See our guide to Michigan cannabis laws for what state law does and doesn't cover, and our cannabis buyer's guide for reading labels and comparing products. If you have questions about a product's THC content, the budtenders at your nearest High Society store can walk you through the label, though nobody can predict a test result. 21+ only. Please consume responsibly.
