For most people, THC drops below detectable levels in blood within a few hours to a couple of days after a single use. If you smoke or vape, blood concentrations peak within about 10 minutes and fall rapidly over the next few hours. Regular, heavy users are a different story: THC and its breakdown products have been detected in blood up to 30 days after last use.
The wide range exists because THC doesn’t simply pass through your body and leave. It’s fat-soluble, meaning it gets absorbed into fatty tissues and then trickles back into your bloodstream slowly over time. How fast that process plays out depends on how often you use cannabis, how you consume it, and your body composition.
What Happens to THC in Your Blood
When you inhale cannabis, THC floods your bloodstream almost immediately, reaching peak levels within about 10 minutes. From there, concentrations drop quickly as your liver begins breaking THC down and your body redistributes it into tissues, especially fat. This initial drop is steep. Within a few hours, blood levels may be a small fraction of their peak.
Your liver converts THC into a secondary compound (often written as THC-COOH in lab results) that is inactive, meaning it doesn’t get you high, but it lingers much longer. While active THC may be undetectable in a casual user’s blood within 12 to 24 hours, the inactive metabolite can remain detectable for days or, in chronic users, up to a month. Whether a blood test looks for active THC, the metabolite, or both matters a lot for how long you’ll test positive.
Occasional Users vs. Daily Users
If you use cannabis once or a few times a month, active THC is typically detectable in blood for roughly 2 to 12 hours after use. By the next day, most occasional users will have blood levels low enough to fall below standard testing cutoffs.
Daily or near-daily users build up a reservoir of THC in fat tissue. Each session adds to the supply, and the compound slowly leaks back into the bloodstream between sessions. A 2025 study from the Association for Diagnostics and Laboratory Medicine measured baseline THC levels in 190 regular users who had been told to abstain for at least 48 hours. Even after that abstinence period, 43% still had detectable THC in their blood. Nearly one in four exceeded 2 ng/mL, and about 5% were above 5 ng/mL, thresholds used by some states to define impaired driving. Crucially, those elevated baseline levels did not translate into worse performance on a driving simulator, highlighting how blood THC concentration alone is a poor measure of impairment.
Edibles vs. Smoking or Vaping
The way you consume cannabis changes the timeline significantly. Inhaled THC behaves almost like an intravenous dose: rapid peak, rapid decline. Edibles follow a very different curve. Because THC has to pass through your digestive system and liver before reaching your bloodstream, oral bioavailability is estimated at just 6%. Peak blood concentrations are delayed by 2 to 4 hours and are much lower than what you’d see from smoking the same amount of THC.
The tradeoff is that edibles produce a longer, flatter blood concentration profile. You won’t spike as high, but THC stays in your blood at moderate levels for longer. This means the window during which a blood test could pick up active THC may extend further after edibles compared to inhaled cannabis, even though peak levels are lower.
Body Fat, BMI, and Genetics
Because THC clings to fat cells, people with higher body fat percentages tend to store more of it and release it more slowly. Two people who smoke the same amount on the same schedule can have meaningfully different clearance timelines based on body composition alone. Genetics also play a role: some people’s livers metabolize THC more efficiently than others, speeding up elimination.
Hydration, metabolism, and age all contribute to variation, but body fat is the most studied factor. If you carry more body fat, expect THC to linger in your system longer than average estimates suggest.
Exercise Can Temporarily Raise Blood THC
One counterintuitive finding: exercise can actually bump your blood THC levels up in the short term. A study published in Drug and Alcohol Dependence had 14 regular cannabis users cycle on a stationary bike for 35 minutes at moderate intensity. The exercise triggered a small but statistically significant spike in blood THC, because burning fat releases stored THC back into the bloodstream. The effect was more pronounced in participants with higher BMI.
This doesn’t mean exercise slows your overall clearance. Over time, burning fat should help deplete THC stores. But if you’re facing a blood test in the near term, a hard workout right before could temporarily push your levels higher rather than lower.
Blood Testing Cutoffs and Legal Limits
There is no single universal cutoff for a “positive” THC blood test. Federal workplace testing regulated by the Department of Transportation uses a threshold of 15 ng/mL for the THC metabolite (THC-COOH) in urine-based initial tests, but blood testing cutoffs vary by jurisdiction and purpose.
For driving-related enforcement, six U.S. states use per se laws that set a legal limit of either 2 or 5 ng/mL of active THC in blood. Twelve states have zero-tolerance laws, meaning any detectable amount is treated as a violation. The practical problem is that regular users can exceed these thresholds without being impaired, simply because of the way THC accumulates and slowly clears from the body. A blood draw taken days after your last use could still return a result above a zero-tolerance or per se limit if you’re a frequent user.
Realistic Timelines at a Glance
- Single use, inhaled: Active THC typically undetectable within 3 to 12 hours. Metabolites may linger 1 to 2 days.
- Single use, edible: Active THC may be detectable for 6 to 24 hours due to slower absorption. Metabolites follow a similar 1 to 2 day pattern.
- Moderate use (a few times per week): Active THC may be detectable for 1 to 3 days. Metabolites for up to a week.
- Daily or heavy use: Active THC can persist at low levels for a week or more. The inactive metabolite has been detected up to 30 days after the last use.
These ranges assume standard test sensitivity. Higher-sensitivity assays or zero-tolerance cutoffs will extend the effective detection window for any usage pattern. If you’re preparing for a specific test, the type of test (active THC vs. metabolite, and the cutoff level) matters as much as when you last used.