How does marijuana produce its effects?
THC and other cannabinoid chemicals in marijuana are similar to cannabinoid chemicals that naturally occur in the body. These endogenous cannabinoids (such as anandamide; see figure) function as neurotransmitters because they send chemical messages between nerve cells (neurons) throughout the nervous system. They affect brain areas that influence pleasure, memory, thinking, concentration, movement, coordination, and sensory and time perception. Because of this similarity, THC is able to attach to molecules called cannabinoid receptors on neurons in these brain areas and activate them, disrupting various mental and physical functions and causing the effects described earlier. The neural communication network that uses these cannabinoid neurotransmitters, known as the endocannabinoid system, plays a critical role in the nervous system’s normal functioning, so interfering with it can have profound effects.
For example, THC is able to alter the functioning of the hippocampus (see “Marijuana, Memory, and the Hippocampus”) and orbitofrontal cortex, brain areas that enable a person to form new memories and shift their attentional focus. As a result, using marijuana causes impaired thinking and interferes with a user’s ability to learn and to perform complicated tasks. THC also disrupts functioning of the cerebellum and basal ganglia, brain areas that regulate balance, posture, coordination, and reaction time. This is the reason people who have used marijuana may not be able to drive a car safely (see “Does marijuana use affect driving?”) and may be impaired at playing sports or other physical activities.
THC, acting through cannabinoid receptors, also activates the brain’s reward system, which includes regions that govern the response to healthy pleasurable behaviors like sex and eating. Like most other drugs of abuse, THC stimulates neurons in the reward system to release the signaling chemical dopamine at levels higher than typically observed in response to natural stimuli. This flood of dopamine contributes to the pleasurable “high” that recreational marijuana users seek.
This series of reports simplifies the science of research findings for the educated lay public, legislators, educational groups, and practitioners. The series reports on research findings of national interest.