NIDA for Teens: The Science Behind Drug Abuse
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Marijuana

How Does Marijuana Affect the Brain?

The main chemical in marijuana that affects the brain is delta-9-tetrahydrocannabinol (THC). When marijuana is smoked, THC quickly passes from the lungs into the bloodstream, which carries it to organs throughout the body, including the brain. As it enters the brain, THC attaches to cells, or neurons, with specific kinds of receptors called cannabinoid receptors. Normally, these cells are activated by chemicals that occur naturally in the body. They are part of a communication network in the brain called the endocannabinoid system. This system is important in normal brain development and function.

Most of the cannabinoid receptors are found in parts of the brain that influence pleasure, memory, thinking, concentration, sensory and time perception, and coordinated movement. Marijuana triggers an increase in the endocannabinoid system. One of the effects is a release of dopamine in the brain, which creates the pleasurable feelings or “high.” Other effects include changes in perceptions and mood, lack of coordination, difficulty with thinking and problem solving, and disrupted learning and memory.

Certain parts of the brain have a lot of cannabinoid receptors. These areas are the hippocampus, the cerebellum, the basal ganglia, and the cerebral cortex. (Learn more about these areas and how THC affects them.) The functions that these brain areas control are the ones most affected by marijuana:

Marijuana's Effects on the Brain
  • Learning and memory. The hippocampus plays a critical role in certain types of learning. Disrupting its normal functioning can lead to problems studying, learning new things, and recalling recent events. A recent study followed people from age 13 to 38 and found that those who used marijuana a lot in their teens and continued into adulthood had a large drop in IQ, even if they quit.
  • Coordination. THC affects the cerebellum, the section of our brain that controls balance and coordination, and the basal ganglia, another part of the brain that helps control movement. These effects can affect performance in such activities as sports, driving, and video games.
  • Judgment. Since marijuana can affect decision-making, using it can cause you to do things you might not do when you are not under the influence of drugs—such as engaging in risky sexual behavior— which can lead to sexually transmitted diseases (STDs), like HIV, the virus that causes AIDS—or getting in a car with someone who’s been drinking or is high on marijuana.

When marijuana is smoked, its effects begin almost immediately and can last from 1 to 3 hours. Decision-making, concentration, and memory can suffer for days after use, especially in regular users.2

If marijuana is consumed in foods or beverages, the effects of THC appear later—usually in 30 minutes to 1 hour—but can last up to 4 hours.

Long-term, regular use of marijuana—starting in the teen years—may impair brain development and lower IQ, meaning the brain may not reach its full potential.3,4

Learn more about how the brain works and what happens when a person uses drugs.

2. Crean RD, Crane NA, Mason BJ. An evidence based review of acute and long-term effects of cannabis use on executive cognitive functions. Journal of Addiction Medicine 2011;5:1-8.

3. Zalesky A, Solowij N, Yücel M, et al. Effect of long-term cannabis use on axonal fibre connectivity. Brain 2012;135:2245-55.

4. Meier MH, Caspi A, Ambler A, et al. Persistent cannabis users show neuropsychological decline from childhood to midlife. Proceedings of the National Academy of Sciences U S A 2012;109:E2657-64.