Hair drug tests can detect cannabis for up to 90 days after last use, which is the standard detection window for a 1.5-inch head hair sample. Body hair and repeated heavy use can extend detection to 12 months or longer. The test looks for THC-COOH, a metabolite that enters the hair shaft as it grows.
can cannabis be detected in hair after one use
How long does cannabis stay in hair?
Most head hair tests use a 90-day window because head hair grows about 0.5 inch (1.3 cm) per month. A 1.5-inch segment near the scalp covers roughly three months of growth. Labs can test shorter segments to estimate a narrower timeframe.
How Long Do Cannabis Metabolites Stay in Hair? Detection Window Guide
Body hair grows more slowly and stays in the growth phase longer. That makes body hair a wider detection net, often up to 12 months. Chronic, high-dose users may show detectable THC-COOH beyond 90 days in head hair, though this varies by lab and cutoff.
how long do cannabis metabolites stay in hair
What do hair test cutoffs mean?
Cutoffs are the minimum metabolite levels a lab reports as positive. Common screening cutoffs for THC-COOH are around 1 picogram per milligram (pg/mg), with confirmation at lower levels such as 0.1 pg/mg. A lower cutoff raises the chance of detecting older or lighter use.
A positive or negative result depends on the cutoff, the lab method, and the sample size. A result below the cutoff is reported as negative even if trace metabolite is present. No home remedy reliably removes THC-COOH from hair.
Can CBD products cause a positive hair test?
Full-spectrum CBD products can contain small amounts of THC. Repeated use may allow THC-COOH to accumulate in hair, especially at low cutoffs. CBD isolate products with no detectable THC carry less risk, but label accuracy varies.
Hair tests are highly sensitive and can pick up trace exposure from close contact or shared devices. If you use CBD and face a drug test, choose third-party lab-tested products and review certificates of analysis. This is general information, not legal or medical advice.
What affects how long cannabis stays in hair?
- Use frequency and dose: daily high-THC use tends to produce more metabolite.
- Hair type and growth rate: slower growth can stretch the timeline.
- Body location: head hair covers about 90 days; body hair can cover a year or more.
- Lab cutoff and method: lower cutoffs detect more use.
- External contamination: smoke, residue, or contact can affect results.
How do labs test hair for cannabis?
Collectors cut a small sample close to the scalp, usually about 1.5 inches and the width of a pencil eraser. The lab washes the sample, extracts metabolites, and screens with immunoassay or mass spectrometry. Positive screens are confirmed with GC-MS or LC-MS/MS.
Key takeaways
- Standard head hair detection: up to 90 days.
- Body hair detection: up to 12 months or longer.
- Heavy chronic use can extend the head hair window.
- CBD products with trace THC may contribute to accumulation.