Test-retest stability of cardiovascular and subjective responses to intravenous cocaine in humans

Sixteen male i.v. cocaine users were measured on their cardiovascular and subjective responses to placebo followed on a separate day by 40 mg i.v. cocaine injections. They were retested within 2 weeks, again receiving placebo and 40 mg i.v. cocaine injections in a random order on separate days. Significant increases in baseline (pre-injection) heart rates during the later sessions were interpreted as possibly reflecting conditioning effects. There were no significant differences in post-injection increases in cardiovascular or subjective responses between the initial and later 40 mg conditions, which might have been indicative of tolerance or sensitization development. Test-retest correlations, indicative of response stability, were moderate to high for any particular timepoint for blood pressure, heart rate, and subjective responses, but pre- vs. post-injection change scores were stable across testings on these measures only under placebo. With the possible exception of some subjective responses, there was little evidence of test-retest stability in responses (change scores) to the 40 mg cocaine injection.