“∆⁹ –Tetrahydrocannabinol (∆⁹-THC) and cannabidiol (CBD), major psychoactive constituents of marijuana, induce potentiation of pentobarbital-induced sleep in mice.

We have elucidated the mechanism of enhancement of the anesthetic effect of pentobarbital by cannabinoids.

These results suggest that binding of ∆⁹-THC to the CB₁ receptor is involved in the synergism with pentobarbital, and that potentiating effect of CBD with pentobarbital may differ from that of ∆⁹-THC. We successfully demonstrated that ∆⁹-THC enhanced the anesthetic effect of pentobarbital through the CB₁ receptor.”

https://www.ncbi.nlm.nih.gov/pubmed/30636988

“The pharmacological results indicate the effect of ∆⁹-THC co-administered with pentobarbital was a synergistic, but not additive, action in mice. Further evidence suggests the CB₁ receptor plays an important role as a trigger in potentiating pentobarbital-induced sleep by ∆⁹-THC.”

https://link.springer.com/article/10.1007%2Fs11419-018-0457-2