For most occasional users, THC clears from the blood within 24 hours. If you use cannabis regularly, detectable levels can linger for days or, in heavy use cases, up to a month. The exact timeline depends on how often you use, how you consume it, and your body composition.
Detection Windows for Occasional vs. Chronic Users
After a single smoking session, THC concentrations in blood spike within minutes, then drop rapidly over the next few hours. In occasional users, blood levels typically return to zero within 24 hours. Chronic users tell a different story: research tracking blood THC over time found that chronic consumers still had detectable THC (around 1 ng/mL) even after 24 hours had passed since their last use. For daily or near-daily users, blood tests can pick up THC for 2 to 12 days after stopping, and in extreme cases of heavy, prolonged use, traces have been detected up to 30 days later.
The reason for this gap comes down to accumulation. THC is fat-soluble, so every time you use cannabis, some of it gets stored in fatty tissue throughout your body. Occasional users don’t build up much of a reservoir. Chronic users do, and that reservoir slowly leaks THC back into the bloodstream even after they stop using.
What Blood Tests Actually Measure
Blood tests can look for two different things: active THC (delta-9-THC) or its inactive breakdown product, THC-COOH. Active THC is what causes impairment and peaks shortly after use. It’s cleared from blood relatively quickly because your liver converts it into metabolites. THC-COOH, the main metabolite, sticks around longer in blood but doesn’t produce a high.
This distinction matters for legal purposes. Some states set limits based on active THC, others on the metabolite, and the cutoff values differ. Ohio, for example, sets its legal driving limit at 2 ng/mL of active THC in whole blood, while its per se limit for the metabolite is 50 ng/mL. States like Colorado and Washington use a 5 ng/mL threshold for active THC. Knowing which compound a test targets helps you understand what the result actually means.
Smoking vs. Edibles
How you consume cannabis changes the blood concentration curve significantly. When you smoke or vape, THC enters the bloodstream through the lungs within minutes, producing a sharp peak that fades over 1 to 3 hours. Edibles take a completely different path: they pass through the digestive system and liver before reaching the blood, with onset typically taking 30 to 90 minutes (faster for cannabis beverages or sublingual products, which can kick in within 15 to 45 minutes).
Because edibles are absorbed more slowly, THC enters the blood at lower peak levels but stays elevated longer. The effects of edibles typically last 4 to 8 hours, sometimes longer at higher doses. This extended absorption means THC may remain detectable in blood for a longer window after eating an edible compared to smoking the same amount.
Why Body Fat and Metabolism Matter
THC’s fat solubility is the single biggest reason detection times vary so much from person to person. After THC enters your bloodstream, it rapidly distributes into tissues, with a particular affinity for fat cells. Your body then slowly releases stored THC back into the blood as those fat cells break down through normal metabolic processes.
This release isn’t constant. Anything that triggers your body to burn fat can temporarily increase blood THC levels, even days after your last use. Research published in the journal Drug and Alcohol Dependence demonstrated this directly: when rats that had been repeatedly exposed to THC were subjected to fasting for 24 hours or given a stress hormone that promotes fat breakdown, their blood levels of both THC and its metabolite rose measurably. In practical terms, this means intense exercise, crash dieting, or periods of high stress could briefly push stored THC back into your bloodstream.
People with higher body fat percentages tend to store more THC and release it over a longer period. Faster metabolisms clear it more quickly. Age, sex, and genetics also play a role, since they all influence how efficiently your liver processes THC and how much fat tissue is available to absorb it.
Rough Timeline by Usage Pattern
- Single use: THC is typically undetectable in blood within 12 to 24 hours.
- Occasional use (a few times per week): Expect a detection window of 1 to 3 days.
- Daily use: THC may remain detectable for 1 to 2 weeks after stopping.
- Heavy, long-term use: Detection is possible for up to 30 days in some cases, though most people clear it sooner.
These ranges assume standard blood testing sensitivity. More sensitive lab equipment with lower detection thresholds can extend these windows. The cutoff used by the testing lab, whether it’s 1 ng/mL, 2 ng/mL, or 5 ng/mL, directly affects whether a result comes back positive or negative at any given point in the clearance timeline.
Blood Tests Compared to Other Test Types
Blood testing has a relatively short detection window compared to urine or hair testing. Urine tests, which look for THC-COOH rather than active THC, can detect use for 3 to 30 days depending on frequency. Hair tests can go back roughly 90 days. Saliva tests fall somewhere between blood and urine, generally detecting use within the past 24 to 72 hours.
Blood tests are most commonly used in roadside impairment testing and hospital settings because they reflect recent use more accurately than urine. If you’re facing a blood draw for employment screening, that’s relatively uncommon since most workplace drug tests use urine. If the concern is a traffic stop or legal proceeding, the active THC threshold in your state is what matters most.