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Welcome to Just Answer and thanks for your question. Hair follicle tests are run via GC/MS (gas chromatography/mass spectrophotometry where every chemical is different, and differentiating between them is even more accurate than fingerprint analysis. Unless the samples were somehow switched in the chain of custody with another person's sample, then if amphetamines and methamphetamine were found, then those were the drugs that had been used at some time in the past 3 months. There are no false positives with GC/MS analysis.