Which substance is sometimes used as a cutting agent for Marijuana?

The correct answer is THC. Tetrahydrocannabinol (THC) is the primary psychoactive compound found in marijuana, but it can also be used as a cutting agent in synthetic cannabis products. In some instances, when creating illicit marijuana or synthetic cannabis to mimic its effects, manufacturers may use THC as part of the mixture to enhance potency or create an appealing product for users. This practice can be seen in various forms of marijuana products where additional THC is introduced to increase the desired effects.

Other substances listed, like PCP and heroin, are not typically used as cutting agents for marijuana. PCP is a dissociative anesthetic that poses significant health risks and does not serve the role of a cutting agent. HCG (human chorionic gonadotropin) is a hormone that is unrelated to marijuana and not used in this context. Thus, the understanding of THC as a substance that can act as a cutting agent highlights its role in the illicit drug market, especially concerning the production and distribution of marijuana-related products.