The active ingredient in marijuana is delta-0-tetrahydrocannabinol (THC). THC mimics the action of the natural neurotransmitter N-arachidonoyl ethanolamide (anandamide).  Anandamide binds to CB1 cannabinoid receptors throughout the brain and CB2 receptors in the body. CB2 receptors have a role in regulating immune function. CB1 receptors impacts mood, memory, appetite, pain, and cognition.