When it comes to polarizing health topics, few subjects spark more debate than weed (except maybe CrossFit or the Paleo Diet). Can it improve your health? Lower stress? Make you more forgetful? Even make you skinnier?

The science is still, well, hazy—but some research is starting to give us an idea of what exactly weed does to the human body.

For instance: Toking up regularly could dull your emotional response and cause addiction, according to a marijuana study from the University of Michigan Health System. Researchers analyzed 108 people in their early 20s (69 men and 39 women), all of whom were taking part in a larger study of substance use. In the study, participants sat in an MRI while they played a game, in which they pressed a button when they saw a target on a computer screen cross in front of them. Before each round, they were told they could win 20 cents or $5—or they might lose that amount, or have no reward or loss. Scientists assessed the moment of anticipation (a.k.a. when volunteers knew they could get a few dollars richer).