11-nor-tetrahydrocannabinol-9-COOH is detectable by immunoassay 3-5 days after a single use of which substance?

• A. Methamphetamine
• B. Cocaine
• C. Benzodiazepine
• D. Marijuana

Answer: (D)

The key idea is that urine immunoassays screen for a drug’s specific metabolite rather than the parent drug itself, and detection windows depend on how that metabolite is formed and cleared. For cannabis, the important metabolite is 11-nor-9-carboxy-THC (THC-COOH). After marijuana use, THC is metabolized to THC-COOH, which remains detectable in urine for several days. A 3–5 day window after a single use fits cannabis exposure because THC-COOH is the metabolite these immunoassays target, so a positive result in that window points to marijuana.

The other substances listed don’t produce this metabolite, and immunoassays for them screen for different compounds. Thus, a 3–5 day detectable immunoassay result is characteristic of marijuana, not methamphetamine, cocaine, or benzodiazepines.