After a single use, THC typically becomes undetectable in blood within 3 to 6 hours if you smoked or vaped, and within 6 to 20 hours if you ate an edible. For daily users, the picture is dramatically different: THC can remain detectable in blood for weeks, with a median last detection time of 22 days in one controlled study of chronic smokers.
These numbers vary based on how much you use, how you consume it, your body composition, and the sensitivity of the test. Here’s what the research shows for each scenario.
Single Use: Blood Clears Within Hours
When you smoke or vape cannabis once, THC floods the bloodstream fast. Blood levels peak within about 10 minutes and can reach anywhere from 15 to 192 ng/mL depending on the dose. But the drop-off is equally sharp. In controlled studies, blood THC returned to baseline within 3 to 6 hours after a single smoking session. By 22 hours, only 10% of whole-blood samples still showed detectable THC.
Edibles follow a different curve. THC from oral consumption enters the blood more slowly, peaking 2 to 3 hours after you eat it, and the peak levels are far lower (never exceeding 5 ng/mL in controlled studies, compared to peaks of 42 to 87 ng/mL from smoking). The tradeoff is that it lingers longer: blood levels from a single oral dose can take 6 to 20 hours to return to baseline.
Regular Users: Days to Weeks
If you use cannabis daily, THC accumulates in your body and seeps back into the bloodstream long after your last session. A National Institutes of Health study monitored chronic daily smokers in a controlled setting where no new cannabis was consumed. The median time to the last positive blood test was 22 days. Two participants still had detectable THC on day 30. One person maintained blood concentrations above 1 ng/mL for 12 consecutive days.
Even within this group, there was wide variation. Fewer than half of the participants had positive blood samples after 16 days, but some kept testing positive well beyond that. The takeaway: if you’ve been using daily for months or years, expect THC to show up in blood for at least two to three weeks, and possibly a full month.
Why THC Lingers in the Body
THC is fat-soluble. After entering your bloodstream, it quickly moves into fat tissue throughout the body. From there, it slowly leaks back into the blood over days or weeks. This is why the plasma half-life of THC (the time it takes for blood levels to drop by half) is so different depending on usage: 1 to 3 days for occasional users, but 5 to 13 days for chronic users. Heavier, longer-term use means more THC stored in fat, which means a longer trickle back into circulation.
Body fat percentage matters here. People with more fat tissue have more storage capacity for THC, which can extend clearance time. Interestingly, anything that triggers your body to burn fat, like intense exercise or fasting, can actually release stored THC back into the blood at higher-than-normal levels. This won’t get you high again, but it can push blood concentrations up enough to affect a test result.
THC vs. Its Metabolites
Blood tests can look for different things. Delta-9-THC is the active compound, the one that causes psychoactive effects. Your liver breaks it down into other compounds, the most important being THC-COOH, an inactive metabolite. These two have very different timelines in blood.
Delta-9-THC peaks quickly and drops fast. THC-COOH, by contrast, rises slowly, peaks around two hours after smoking, and plateaus for an extended period before declining. Some blood tests measure only delta-9-THC (particularly in legal driving contexts), while others measure metabolites as well. Which compound the test targets directly affects whether you’ll pass.
Legal Thresholds and What They Mean
Several U.S. states, including Colorado and Washington, set a legal limit of 5 ng/mL of delta-9-THC in whole blood for driving. Twelve additional states have zero-tolerance laws, meaning any detectable THC (as low as 0.5 ng/mL) can result in a charge.
This creates a real problem for regular users. The NIH study found that chronic daily smokers can exceed the zero-tolerance threshold for weeks after their last use, and can stay above 1 ng/mL for nearly two weeks. A daily user who hasn’t consumed cannabis in a week could still test above legal limits in some states, despite no longer being impaired. Unlike alcohol, where blood alcohol levels directly correlate with intoxication, the relationship between blood THC concentration and actual cognitive impairment remains unclear. Detection in blood does not mean you are currently high.
Estimated Detection Windows at a Glance
- Single use, smoked or vaped: 3 to 12 hours in most people, up to 24 hours in some
- Single use, edible: 6 to 20 hours
- Moderate use (a few times per week): 1 to 3 days
- Daily or heavy use: 7 to 30 days, with a median around 22 days
These ranges assume standard laboratory sensitivity. More sensitive tests will extend these windows, less sensitive ones will shorten them. Your metabolism, body fat, hydration, and the potency of what you consumed all shift the timeline in one direction or the other. The single biggest factor is frequency of use: a one-time user and a daily user are operating on completely different biological clocks when it comes to clearing THC from blood.