Cannabidiol interactions with Δ-9-tetrahydrocannabinol on antinociception after carrageenan-induced inflammatory pain in male and female rats

Cannabis products used for pain typically contain Δ-9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD) in varied amounts, but data on the effects of specific cannabinoid formulations on different pain types are lacking. This study used the carrageenan-induced inflammatory pain model to test oral Δ9-THC, CBD, or their combination on acute edema and pain hypersensitivity. Male and female Sprague–Dawley rats (n = 10–14 per sex/group) were pretreated (1 hour) with vehicle (sesame oil), Δ9-THC (1, 3, and 10 mg/kg, p.o.), CBD (10, 30, 100 mg/kg, p.o.), or select doses of Δ9-THC + CBD combinations prior to an intraplantar λ-carrageenan injection into the hind paw. The nonsteroidal anti-inflammatory drug ketoprofen (10 and 20 mg/kg i.p.) or its vehicle (1:1:18 ethanol:Cremophor EL:saline [Millipor Sigma]) was administered to a separate group as a positive control. Measurements were conducted at baseline and 1, 3, and 5 hours after carrageenan injection. Carrageenan produced edema and hypersensitivity to radiant heat (hyperalgesia) and mechanical pressure (allodynia). Δ9-THC alone sex- and dose-dependently decreased hyperalgesia and allodynia but not inflammation, with effects of Δ9-THC being greater in females than males, and the lowest Δ9-THC dose was proinflammatory in males. CBD alone did not affect pain sensitivity but had modest anti-inflammatory effects in males. Isobolographic and dose addition analyses indicated Δ9-THC + CBD was subadditive relative to Δ9-THC alone. These data demonstrate that prophylactic oral Δ9-THC alleviates acute inflammatory pain with sex-dependent effects, and CBD diminishes Δ9-THC antinociception when combined. The findings suggest oral Δ9-THC is superior to CBD or combined Δ9-THC + CBD for acute inflammatory pain. Significance Statement: Despite the popularity of cannabis for pain management, empirical data on how specific cannabinoid formulations affect acute inflammatory pain are limited. This study in rats found that pure Δ-9-tetrahydrocannabinol (Δ9-THC) formulations were most effective at improving inflammatory pain compared to pure cannabidiol or Δ9-THC + cannabidiol combinations, and females were more sensitive than males to the antinociceptive effects of Δ9-THC.