Observer ratings were completed by trained research assistants who were blinded to the drugs being administered. Observer ratings were conducted before dosing and 0.5, 1, 2, 3 and 4 h after dosing. Ratings were based on the overall level of effect that the staff member observed on each item since the last rating, based on observation of the participant's behavior rather than on the participant's verbal reports or ratings. The participant was rated on a 5-point scale, from 0, indicating normal, to 4, indicating extreme impairment or disruption, on 8 dimensions (e.g., sedation, strength of drug effect; see Evans et al., 1990 for details). A total observer-rating score was calculated by taking the sum of the 8 items at each time point. Heart rate and blood pressure were measured after approximately a 30-min rest period before each assessment battery while participants were in a seated position using a Sentry II vital signs monitor (Model 6100; NBS Medical Services, Costa Mesa, CA).
