This depends on the drug you are taking:
Marijuana: take 500mg of niacin(vitamin b3) once a day or a few days before your test. RESEARCH THIS FIRST
Amphetamines: take vitamin c or citric acid because the acid helps the drug metabolize faster in your system
Any other drugs I'm really not sure of a foolproof way of passing
Google whatever drug you're trying to pass for
Hope I helped a little
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