New research released this week from the University of Pretoria has confirmed that the prescription drug Efavirenz (brand name Sustiva or Stocrin), an antiviral medicine used in the treatment of human immunodeficiency virus (HIV), cross-reacts in urine screens with tetrahydrocannabinol (THC), the active ingredient in marijuana.
Accordingly, the most widely used urine screening tests cannot distinguish between a prescription antiviral medication and cannabis. Individuals subject to urine screening for court, or employment, should insist on a confirmatory gas chromatography – mass spectrometry (GC – MS) test, particularly when cross-reactivity with prescription medication is suspected.
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