Does Cannabis Show in a Hair Follicle Test? | Reddit Facts

Short answer

Yes. A hair follicle test detects THC-COOH, the metabolite the body makes after THC enters the blood. The detection window is longer than urine or saliva. For head hair, a standard test covers about 90 days. Reddit threads about this topic are personal reports. They are not lab results.

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What the test measures

Labs take a sample of head hair, about 1.5 inches (3.8 cm) long, cut close to the scalp. Head hair grows about 0.5 inch (1.3 cm) per month. A 1.5 inch sample covers about 90 days. The lab washes the sample, digests it, and runs an immunoassay screen. A positive screen goes to GC-MS or LC-MS/MS confirmation.

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THC-COOH enters hair through the follicle during growth. Small amounts also reach the shaft from sweat and sebum.

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Detection window

• Head hair: about 90 days at 1.5 inches.
• Body hair: slower growth, so the window can reach 6 to 12 months.
• Recent use: THC may not appear for about 7 days, because the hair needs time to grow.

A hair test does not show impairment. It shows exposure in the past.

Cutoff levels

The proposed federal guidelines from the Department of Health and Human Services list a screen cutoff of 1 picogram per milligram (pg/mg) for THC-COOH and a confirmation cutoff of 0.1 pg/mg. One picogram is one trillionth of a gram. Labs set their own limits inside that range.

What Reddit users claim

Common claims in Reddit threads include bleaching the hair, detox shampoos, vinegar rinses, the Macujo method, and repeated washing. Some users say they passed. Others say they failed after the same steps.

Published research on cosmetic treatments found that bleach and dye lowered THC-COOH levels in some samples. The treatments did not clear the drug in every sample. Bleach also damages the cuticle. Labs can see the damage and flag the sample.

False positives and CBD

Second-hand smoke at the 1 pg/mg cutoff is rare in lab data. CBD products are a larger risk. Full-spectrum CBD can hold small amounts of THC, and labels do not always match contents.

Practical notes

Water does not flush THC from hair. Drinking fluids dilutes urine, not hair. Shaving the head does not solve the problem. Labs can collect body hair or use a different method. A refusal to give a sample is often treated as a positive result by employers.

Bottom line

Hair tests detect cannabis for about 90 days with head hair. Reddit reports of beating the test exist. No product has FDA approval for this purpose. The final result is a lab number from a confirmed test.