Marijuana Use Can Change Your Brain In An Unexpected Way, New Study Says

by Talia Koren
Jaki Portolese

Smoking weed can often give you a sudden rush of calmness and happiness, but it turns out it might some negative effects on other parts of your brain. 

New research from the University of Michigan has shown that although you may feel happiness from smoking weed in the short term, extended use of the drug can diminish activity in weed smokers' brains when they're presented with a reward. Basically, smoking a lot of weed can make moments that are supposed to make you feel happy and exciting less so.

The study, published in JAMA Psychiatry, shows that the brain's reward system changes under the influence of marijuana. The senior author of the study, Mary Heitzeg, PhD says,

What we saw was that over time, marijuana use was associated with 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.

Just over 100 people in their early 20s participated in the study. Their brains were monitored in an MRI scanner while they played a game that prompted them to click a button when they saw a target on a screen. They were told before each round that they could possibly win a small amount of money, lose money or have no loss or reward.

The researchers were looking to see what happened in participants' brains when they were presented with a monetary reward. With the prospect of a positive outcome, their brains should have been flooding with dopamine, but that wasn't the case with people who reported use of marijuana. Researchers saw consistently subdued responses in the brains of weed smokers when they were promised or given a reward. It's not that they didn't care at all, but compared to non-smokers, there was less brain activity.

Here's the most interesting part, though. Other studies have shown that when people who smoke weed are shown rewards that involve the drug, their reactions are stronger. Meaning, the brain gets more excited for marijuana as a reward than any other kind of reward, like money.

I guess weed smokers truly do care about one type of green over the other.

Citations: Marijuana use dampens brain's response to reward over time, study finds (Science News)