Rosh Psychiatry Board Practice Exam

How does delta-9-tetrahydrocannabinol (THC) primarily function in the brain?

1. Partial agonist at the cannabinoid 1 and cannabinoid 2 receptors

2. Partial agonist at the cannabinoid 2 receptor

3. Pure agonist with high affinity at cannabinoid 1 receptor

4. Pure agonist with very high affinity at the cannabinoid 1 receptor

The correct answer is: Partial agonist at the cannabinoid 1 and cannabinoid 2 receptors

Delta-9-tetrahydrocannabinol (THC) primarily functions in the brain as a partial agonist at both cannabinoid 1 (CB1) and cannabinoid 2 (CB2) receptors. This means that THC binds to these receptors and activates them but does not elicit a maximal response even at high concentrations, which distinguishes it from a full agonist. The action of THC at the CB1 receptors, which are predominantly found in the central nervous system, mediates the psychoactive effects of cannabis, contributing to feelings of euphoria and altered perception. In addition, THC's role as a partial agonist at CB2 receptors, which are mainly located in the peripheral nervous system and immune system, suggests it might have some effects outside of the central nervous system, including potential anti-inflammatory properties. This dual action contributes to the diverse pharmacological profile of THC, influencing various physiological processes and producing both therapeutic and adverse effects. While other answers touch upon aspects of THC’s action, the selection that emphasizes it as a partial agonist at both receptors accurately captures the nuanced effects THC has in the brain and body, without overstating its potency at the CB1 receptor alone.