Table 2

Mean ED₅₀ values and 95% confidence limits for cocaine and heroin administered alone or in various combinations in substituting for the 10:1 cocaine/heroin training combination

Test Drug or Drug Combination	ED₅₀ (mg/kg)	95% Confidence Limit
Cocaine alone	0.48	0.23–0.99
Heroin alone	0.20	0.16–0.26
30:1 cocaine/heroin	0.20 cocaine^2-150	0.10–0.39
	0.0067 heroin^2-151	0.0035–0.013
10:1 cocaine/heroin	0.19 cocaine^2-150	0.12–0.23
	0.019 heroin^2-151	0.019–0.020
3:1 cocaine/heroin	0.090 cocaine^2-150	0.037–0.22
	0.030 heroin^2-151	0.012–0.072

↵2-150 Significantly different from cocaine alone (P < .05).
↵2-151 Significantly different from heroin alone (P < .05).