July 2022 in “Research Square (Research Square)” Hair analysis can somewhat track past testosterone levels but is influenced by factors like hair washing, growth rate, sex, and hair color.
January 2025 in “Scientific Reports” Hair analysis can show changes in vitamin D levels over time.
67 citations
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May 2013 in “Therapeutic drug monitoring” Wait 4-5 weeks after drug use before hair testing and cut hair into three segments to confirm single drug exposure.
September 2023 in “Scientific reports” Segmental hair analysis can track testosterone over time but needs adjustments for sex, hair color, and washing frequency.
30 citations
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March 2012 in “Journal of Analytical Toxicology” THCCOOH levels in hair decrease from root to tip and don't match well with self-reported cannabis use.