The best-supported answer is a terminal plasma half-life of about 1 to 3 days for occasional users and 5 to 13 days for people who use cannabis daily. That range comes from controlled pharmacokinetic studies that track THC and its metabolites in blood over hours and days. The criteria that separate one estimate from another are the study population, the route of administration, the sensitivity of the lab assay, and whether the test measures THC itself or its metabolite THC-COOH.
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What Half-Life Means in a Blood Test
Half-life is the time it takes for the concentration of a drug in blood to drop by half. THC does not follow one clean curve. It has an initial distribution phase measured in minutes, a faster elimination phase measured in hours, and a terminal phase measured in days. The terminal phase matters most for a blood test because it reflects THC leaving fat tissue and re-entering the bloodstream.
Cannabis Drug Test Cutoff Levels: Urine, Oral Fluid, Hair
Option 1: 1 to 3 Days for Occasional Use
This is the range most controlled single-dose studies support for someone who uses cannabis once a week or less.
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- Pros: matches data from casual users, accounts for redistribution from fat, and is easy to apply to a routine blood draw.
- Cons: understates chronic users, does not fit high-dose edibles, and shifts with the lab cutoff.
Use this range if you use once a week or less and need a rough planning window for a blood test.
Cannabis Half-Life and Body Fat: How Long THC Stays Stored
Option 2: 5 to 13 Days for Chronic Daily Use
Repeated exposure saturates fat stores, so the terminal half-life stretches out.
- Pros: fits daily users, explains positive blood results after several days of abstinence, and helps clinicians interpret unexpected positives.
- Cons: too long for light users, changes with body fat and liver enzyme activity, and may not apply if the test only measures THC-COOH.
Use this range if you use daily or nearly daily, especially with concentrates or edibles.
Option 3: About 30 Hours After a Single Moderate Dose
Some sources cite a plasma half-life near 30 hours for a single moderate dose in a person with no recent use.
- Pros: simple number for one-time use, reflects the early elimination phase, and is easy to explain.
- Cons: ignores accumulation from repeated use, skips the terminal phase, and misleads frequent users.
Use this number only for a one-time low dose in a person with low body fat and no recent cannabis use.
Why the Estimates Disagree
- Frequency of use: daily use lengthens the terminal half-life.
- Route: smoked THC peaks fast and clears fast, while edible THC clears slower.
- Body composition: more fat tissue means a longer release phase.
- Assay cutoff: a lower lab cutoff detects THC for more days.
- Analyte: THC and THC-COOH have different half-lives in blood.
Bottom Line
For most blood test questions, use 1 to 3 days for occasional use and 5 to 13 days for chronic daily use. The 30-hour figure is a single-dose number and should not be applied to routine or heavy use. The lab cutoff, not the half-life alone, decides whether a result is positive.