Chemical Hair Treatment Can Increase THC-COOH While Lowering Parent THC
Chemical hair treatment did not move every cannabinoid measurement in the same direction. In an experiment using authentic hair specimens, parent THC usually decreased, while the measured THC-COOH metabolite usually increased. The reason for the increase remains incompletely established.
A laboratory treatment experiment
The researcher selected 100 previously positive head-hair samples for a study of cannabinoids and cocaine-related analytes. Cannabinoid results were available for 99 specimens because one sample had not originally been analyzed for cannabinoids.
Separate groups of approximately ten samples underwent one of nine permanent dye treatments or one bleach treatment. Original and treated portions were compared using LC–MS/MS. This was treatment of collected hair, not additional cannabinoid exposure of the donors.
Parent and metabolite results diverged
THC concentrations decreased in 89% of cannabinoid specimens. THC-COOH concentrations increased in 82%, decreased in 17% and remained unchanged in 1%. These specimen-level proportions describe this selected experiment; they are not the probability of a particular outcome for every salon treatment.
Seven of nine dyes produced significant mean THC-COOH increases. Two showed increases that did not reach significance. Bleach produced a significant decrease instead. The intended dye color showed no consistent relationship to the concentration change.
A proposed mechanism is not a demonstrated pathway
The paper proposed that damaged hair could release more retained material during extraction. It also discussed possible oxidative formation of additional metabolite within the hair.
The experiment did not establish how much each mechanism contributed. In particular, it did not demonstrate that environmental THC contamination alone necessarily generates a positive THC-COOH result after dyeing. The author identified that as a future research question.
Implications for interpreting a changed result
A higher metabolite value after chemical treatment need not mean that the donor consumed more cannabis between measurements. Conversely, this study does not justify a universal numerical correction for treated hair.
Document the treatment history, tested segment, analytes and laboratory procedures. The specimens were previously positive and underwent limited laboratory treatment conditions, so the findings do not establish detection windows, impairment or the circumstances of an individual exposure. Their contribution is showing why both upward and downward analytical changes require consideration.
Related: Interpreting THC concentration and impairment.
Primary research
The Effect of Permanent Dye Colour on Illicit Drug and Metabolite Levels in Chemically Treated Hair. DOI: 10.1002/dta.70098.
