This is Dr. David
the hair sample could have been contaiminated by the drug
there are many drugs which can cause false positive for meth
I included an article about it
cold medications with brompheniramine or phenylpropanolamine can cause false positives.
I bet his nyquil cold medications contained ingredients which caused this false positive
all hair screening tests which are positive have to be confirmed by a MS/GC mass spectroscopy/gas chromatography confirmatory test
if he doesn't use meth, his confirmatory test will be negative.
let me know if you have other questions.
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