Cannabis metabolites stay detectable in head hair for roughly 90 days, which is the window a standard 1.5 inch (3.9 cm) hair sample covers. Occasional users may drop below the lab cutoff sooner, and daily long-term users tend to stay positive across the full three months. Body hair holds metabolites longer because it grows more slowly. The deciding factors are how much and how often someone uses, the length and type of hair collected, and the cutoff the laboratory applies.
Does a Hair Drug Test Show How Long You Used Cannabis?
How hair testing captures cannabis use
Blood vessels feed the follicle, and trace amounts of drug metabolites circulate through it as the hair shaft forms. Those metabolites become locked inside the keratin structure. Because the shaft grows about half an inch (1.25 cm) per month, each segment of hair maps to a rough period of use. A lab that cuts the closest 1.5 inches is reading the last three months. Screening usually happens with an immunoassay, and any positive is confirmed with GC-MS/MS or LC-MS/MS.
how long does cannabis stay in hair
Detection windows by use pattern
- Single use or very occasional use: often 30 days or less, sometimes not detected at all
- Weekly use: about 30 to 60 days
- Daily or near-daily use: up to 90 days
- Heavy chronic use with long hair: 90 days and beyond if longer segments are tested
These are ranges, not guarantees. A person who uses once and has slow-growing hair can still test positive near day 85, while a moderate user with faster growth might fall under the cutoff earlier.
Head hair, body hair, and nails
Head hair is the standard sample because its growth rate is predictable. Body hair grows more slowly and stays in the growing phase longer, so it can hold metabolites well past the 90 day mark. Labs rarely use body hair for that reason, but it happens when head hair is too short to collect. Nail clippings and toenail samples behave in a similar way and can carry a longer window than head hair.
how long does cannabis stay in hair
Cutoffs and why they matter
Hair testing is far more sensitive than urine testing. Federal hair testing guidelines that were proposed set an initial screening cutoff of 1 pg/mg and a confirmatory cutoff of 0.1 pg/mg for the marijuana metabolite, and many commercial labs work in that same range. A result below the cutoff is reported as negative even when some metabolite is present. This is why two people with similar use can get different answers from different labs.
Does CBD show up on a hair test
CBD isolate products should not trigger a THC metabolite result because they contain no THC. Full-spectrum hemp products can legally contain up to 0.3 percent THC, and repeated daily use of a high-dose full-spectrum product can add up. Hair cutoffs sit at a fraction of a picogram per milligram, so a heavy full-spectrum routine carries some theoretical risk even when the label says hemp-derived. If a drug test matters for work or legal reasons, isolate-based CBD is the safer choice.
What changes the result
- Frequency and dose: the single biggest factor
- Metabolism and body fat: THC is stored in fat and released over time
- Hair growth rate: faster growth moves older metabolites out of the tested segment
- Chemical treatment: bleach, dye, and relaxers damage the shaft and can lower detectable levels, though labs screen for tampering
- Secondhand smoke: exposure at these cutoffs is a weak contributor, not a common cause of positives
- Collection length: a lab that takes 3 inches reads a much longer history than one that takes 1.5 inches
Pros and cons of hair testing for cannabis
Pros
- Wide detection window compared with urine or saliva
- Harder to cheat than a urine sample
- Can show a pattern of chronic use rather than a single recent day
Cons
- Cannot prove impairment on the day of collection
- Costs more than urine screening
- Cutoff differences between labs create inconsistent results
- Cosmetic hair treatments can skew results in either direction
Bottom line
Plan on 90 days as the working answer for head hair, with 30 days as a realistic best case for light, one-time use. Body hair and nails stretch the window further. Anyone buying CBD who faces a drug test should stick to THC-free isolate products, keep dosing moderate, and expect the hair test to reflect the past three months rather than the past few days.