For all those who strongly advocate the legalization of marijuana, a recent study might come as a major surprise. The study by the University of Michigan Medical School claimed that using cannabis for a long time can actually dampen the brain’s response to reward. Under the influence of marijuana, it is normal for a person to be upbeat due to the effect of cannabis on areas of the brain that respond to rewards.
However, with prolonged use of marijuana that high doesn’t last too long, said the study. With time, users would develop tolerance and gradually start abusing it. The dampened and blunted response after some time may increase the risk of addiction to it or other drugs, the researchers said.
The first long-term study, published in the JAMA Psychiatry in July 2016, evaluated young marijuana users and tracked their brains’ responses to rewards over a period of time. The study found that there are measurable changes in the brain’s reward system caused by marijuana use. The changes were observed without taking into account other factors like alcohol use and cigarette smoking.
Marijuana use may hijack the reward system
Senior author of the study and U-M neuroscientist Mary Heitzeg, Ph.D., said that over time, marijuana use leads to a lower response to a monetary reward. “This means that something that would be rewarding to most people was no longer rewarding to them, suggesting but not proving that their reward system has been ‘hijacked’ by the drug, and that they need the drug to feel reward-or that their emotional response has been dampened,” she said.
The study that involved 108 people in their early 20s monitored their brain scans for over a period of four years. The volunteers were made to play a game at the time of scanning their brains and were told they might win some amount of money in the game. The investigators wanted to study the response of the reward centers of the volunteers’ brains called the nucleus accumbens. They observed that cells of the nucleus accumbens usually swing into action in anticipation of the reward.
Marijuana tied to lower response in nucleus accumbens
The researchers found that the more marijuana a volunteer used, the smaller was the response in his or her nucleus accumbens over time. Previous studies have shown that people who use high-inducing drugs very often also respond strongly after getting any cue related to the drug. Once that happens, it means it is harder to quit that particular drug.
And if that happens and holds true for marijuana users, it might spell trouble for them as well. “It may be that the brain can drive marijuana use and that the use of marijuana can also affect the brain. We’re still unable to disentangle the cause and effect in the brain’s reward system, but studies like this can help that understanding,” said author Meghan Martz, a doctoral student in developmental psychology at U-M.
Apart from bringing changes in the reward system over time, marijuana use also impacts the emotional functioning of a person, the researchers said.