The next day (Day 2) all participants underwent an extinction session in which one of the CS+s (e.g., blue square) was extinguished (CS+E) whereas the other CS+ (e.g., yellow square) was not (CS+U). Approximately 120 minutes prior to initiation of extinction training participants ingested an opaque gelatin capsule (size 00) with dextrose filler that contained either synthetic THC (Marinol; 7.5 mg; Solvay Pharmaceuticals, Marietta, GA) or dextrose alone (placebo; PBO) [PBO, 123.80 ± 3.19 min; THC, 119.36 ± 2.45 min]. The timing insured presence of peak subjective effects and plasma levels of THC (Wachtel et al., 2002) during the extinction training. The THC dose used is the lowest effective dose found to produce behavioral and subjective effects (Kirk and de Wit, 1999; Phan et al., 2008; Rabinak et al., 2011; Wachtel et al., 2002). During extinction learning the CS+E was presented in the absence of the US, whereas the CS+U was not presented. There were 15 CS+E and 15 CS− trials.
