How long do cannabis metabolites stay in hair?
Most standard hair drug tests can detect cannabis metabolites for about 90 days. That window matches the common lab sample of 1.5 inches (3.8 cm) of scalp hair, which represents roughly three months of growth. Heavy, chronic use can push detection beyond 90 days. Body hair can retain metabolites much longer because it grows slower.
Does a Hair Drug Test Show How Long You Used Cannabis? A CBD Buyer's Guide
What a hair test looks for
Labs test hair for THC-COOH, the main carboxy metabolite of delta-9 THC, not just parent THC. After use, metabolites enter the bloodstream and are deposited into the hair follicle as hair grows. Scalp hair grows about 1 cm per month. A standard 1.5-inch sample therefore covers about 90 days of exposure.
how far back can a hair drug test detect cannabis
Detection window by hair type and use pattern
- Scalp hair, standard 1.5-inch sample: about 90 days.
- Scalp hair, longer sample or slow growth: can exceed 90 days, especially with heavy chronic use.
- Body hair: up to 12 months in some cases because growth is slower and retention is longer.
- Occasional use: may fall below the cutoff sooner, but this is not a reliable pass.
Factors that affect how long metabolites stay
- Frequency and dose: daily high-THC use leaves more residue than one-time use.
- Hair growth rate: slower growth stretches the calendar window.
- Hair treatment: bleaching, dyeing, and relaxing can damage hair and alter results, but they do not reliably remove metabolites.
- Test cutoff: a lower cutoff, such as 1 pg/mg, catches more use than a higher cutoff.
- Sample length and body site: longer samples and body hair widen the window.
Does CBD affect a hair test?
CBD itself is not the target of standard cannabis hair tests. The target is THC-COOH. Full-spectrum CBD can contain small amounts of THC. Repeated use of a product with trace THC could add exposure, but the effect on a hair test depends on dose, product, and lab cutoff. CBD isolate carries lower THC risk. Check a batch-specific COA before assuming a product is THC-free. This is general information, not a guarantee about any test result.
What does not reliably clear hair
Detox shampoos, vinegar rinses, and home remedies do not have consistent evidence for removing THC-COOH from hair. Harsh treatments can damage the sample and may prompt a lab to collect a new sample. No shampoo or supplement is a proven way to shorten the detection window.
can cannabis be detected in hair after one use
Practical timeline
- Identify the sample type. Standard scalp hair tests usually cover about 90 days.
- Add time for heavy chronic use. Allow for detection beyond 90 days when use was daily or concentrated.
- Add more time for body hair. Body hair can reflect a window up to 12 months.
- Check the test cutoff. A 1 pg/mg cutoff is more sensitive than higher thresholds.
- Treat any clean timeline as an estimate. Lab methods, hair growth, and use history change the result.