How Marijuana Affects the Brain

Julie Shenkman
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THC, the psychoactive chemical in marijuana, causes shrinking in the orbitofrontal cortex region of the brain. This area of the brain is responsible for making good — or bad — decisions. The orbitofrontal cortex contains cannabinoid receptors that allow the psychoactive chemical to bind to the area. Researchers study how marijuana works in the brain to determine positive and negative effects.

Regular marijuana usage decreases the number of receptors in the orbitofrontal cortex in order for the area to regain balance. Overabundance of THC leads to less receptors, thus compromising how a person makes a decision. It also builds a resistance to marijuana, requiring a person to use more in order to achieve the same effects.

The findings about the way marijuana affects the orbitofrontal cortex region of the brain leads some researchers to believe that marijuana is mentally and physically addictive. A percentage of users report cravings for marijuana and slight withdrawal symptoms, such as irritability, after ceasing use. Marijuana retailers in states where the substance is legal, such as Colorado, may benefit from people who excessively use and crave marijuana. Marijuana tourism and regular users in the state allow the retailers to raise the price of the substance, because the retailers know that users are likely to pay high amounts. The fact that people are willing to pay double or triple the street price for marijuana is another indicator that the substance is possibly addictive.

Whether or not marijuana is addictive, there is no evidence that the effects on the orbitofrontal cortex cause a change in IQ levels or intelligence of the user. A test performed on marijuana users and non-marijuana users found that IQ levels were lower in those who used. The test was inconclusive, however, because it was possible that other unknown factors caused the lower scores. In another study, marijuana smokers displayed escalated connectivity in the orbitofrontal cortex. This increased connectivity improves communication in the network of the orbitofrontal cortex and other parts of the brain. The most positive connectivity effects occurred in people who began smoking marijuana during adolescence. However, after about 6 years of continuous marijuana usage, the connection reverses.

The studies performed on how marijuana affects the brain also give researchers a better understanding of how the substance can benefit people who suffer from certain mental or physical health conditions.

As of 2014, researchers continue to study the effects of marijuana on the brain. The legalization in some states allows scientists to perform more tests on occasional and chronic marijuana users. Researchers are finding new information on how THC alters the way a person thinks and acts. Arguments exist on whether or not the substance is addictive, especially since only some marijuana users seem to experience cravings and withdrawal symptoms.


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