Contrary to what many advertised drug tests might promise, not all substances leave their telltale chemical signature in the body for the same amount of time.
The moment we take a drug — whether we snort, smoke, or swallow it — our bodies begin to break it down. In the process, metabolites, or byproducts, of the drug are produced, which can linger in our blood, urine (and even in our hair) for long after the initial effects of the drug are felt. Traces of these metabolites are what drug testers look for, since they’re a good indication that someone has actually used a drug rather than merely come into accidental contact with it.
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Source Credits: Erin Brodwin and Dragan Radovanovic in Business Insider. Photo by flyingpingu69 in Deviantart