Which of the following most accurately reflects the evidence regarding driving after using marijuana?

• A. There is no increased crash risk after cannabis use; epidemiologic studies show no association after adjustment for confounders.
• B. Acute cannabis impairment is on average similar to driving at a blood alcohol concentration of 0.08%, so crash risk is equivalent to legal alcohol intoxication.
• C. Acute cannabis use modestly impairs driving, slightly increases crash risk, and combined use with alcohol further increases risk; blood THC poorly predicts impairment.
• D. Detection of any blood THC after driving reliably indicates impairment and justifies per‑se DUI enforcement at any detectable level.

Answer: (C)