Table 1.

ED₅₀ values and 95% confidence limits for Δ⁹-THC and anandamide, alone and in combination with URB 597, in monkeys discriminating Δ⁹-THC (0.1 mg·kg⁻¹ i.v.) from vehicle

Drug	ED50 value (95% CL) in mg·kg−1	Potency ratio (95% CL)†
Δ9-THC	0.039 (0.022–0.072)
+URB 597 (1 mg·kg−1)	0.024 (0.015–0.038)	1.6 (0.8–3.5)
+URB 597 (3.2 mg·kg−1)	0.072 (0.029–0.18)	0.5 (0.2–1.4)
Anandamide	5.8 (2.7–13)
+URB 597 (0.32 mg·kg−1)	1.9 (0.38–9.0)	3.1 (0.3–28)
+URB 597 (1 mg·kg−1)	0.45 (0.11–1.8)*	13 (2.1–99)
+URB 597 (3.2 mg·kg−1)	0.18 (0.056–0.57)*	32 (7.8–140)

^*Significant increase in potency.

^†Potency ratios and 95% confidence limits (CL) are the ED₅₀ values of the agonist alone divided by the ED₅₀ value of the agonist in combination with URB 597.