It’s possible to test positive for illegal drugs without taking one.

This is true...at least when it comes to initial urine SCREENING tests.

Certain substances can cause false positives on urine immunoassay-based screens...but the same sample will come back negative with a stricter laboratory-based test such as gas chromatography-mass spectrometry (GC-MS) or high-performance liquid chromatography (HPLC).

SCREENING tests for opiates and amphetamines often result in false positives.

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