The psychoactive properties of cannabinoids are well known, and there are controversies over whether cannabinoids can be used for therapeutic purposes worldwide. Δ⁹-tetrahydrocannabinol ( THC) is the main psychoactive substance in cannabis. The neurological mechanisms of THC were only recently discovered, and its neurological mechanism of action is still not fully understood. The blood-brain barrier (BBB) is a very important structure protecting the brain and is the first line of defense preventing foreign substances from entering the brain. THC’s lipophilic nature and its interaction with the endocannabinoid system make it more likely to act on the BBB. In this paper, we review the neurotoxic effects of THC, focusing on its effect and mechanism of action on the BBB, and provide a theoretical basis for studies elucidating the neural mechanism of THC.