TABLE 1.

Group mean ED₅₀ values for each μ-opioid receptor agonist alone or in combination with Δ⁹-THC or CP 55,940 with 54°C water and group mean potency ratios for the combinations

Opioid Agonists	Control ED₅₀ (95% CL)^{^a}	Pretreatment with a Cannabinoid Receptor Agonist
		Δ⁹-THC (1.0 mg/kg)		CP 55,940 (0.032 mg/kg)
		Test ED₅₀ (95% CL)	Potency Ratio (95% CL)^{^b}	Test ED₅₀ (95% CL)	Potency Ratio (95% CL)^{^b}
Etorphine	0.00065 (0.00039–0.0011)	0.000078 (0.000020–0.00029)	12.43 (0.02–24.84)	0.000047 (0.000020–0.00010)	19.65 (2.57–36.73)^{^c}
Fentanyl	0.042 (0.019–0.088)	0.0024 (0.00074–0.0078)	20.60 (6.63–34.56)^{^c}	0.00088 (0.00036–0.0022)	52.99 (26.91–79.08)^{^c}
Morphine	5.24 (4.32–6.37)	1.64 (1.28–2.10)	3.37 (2.28–4.46)^{^c}	0.84 (0.42–1.66)	7.91 (2.33–13.48)^{^c}
Buprenorphine	0.93 (0.31–2.81)	0.24 (0.10–0.58)	5.42 (2.08–8.76)^{^c}	0.25 (0.090–0.67)	4.08 (2.17–6.00)^{^c}
Nalbuphine	2.40 (0.096–59.67)	7.33 (1.02–52.54)	0.55 (0.06–1.04)	1.18 (0.097–14.22)	3.58 (−1.05–8.21)

CL, confidence limit.
↵^a ED₅₀ expressed in milligrams per kilogram.
↵^b Potency ratios were calculated for individual subjects by dividing the control ED₅₀ by the test ED₅₀ and then averaged for the group.
↵^c Shifts in dose-effect curves were considered statistically significant if the 95% confidence limits of the potency ratios, averaged across monkeys, did not include 1.