Legalizing pot leads to increased marijuana use, according to a new study from the University Colorado Boulder and the University of Minnesota.

The study, published Thursday in the journal Addiction, showed that marijuana use rose nearly 25% in states where recreational marijuana is legal compared to states where it is banned.

Researchers wanted to find out how much marijuana use increases when lawmakers legalize recreational use, and they also wanted to see how that impacts people’s health in the long run.

The study documented marijuana use among 3,400 adult twins before and after 2014, the year Colorado became the first state to legalize recreational marijuana. Researchers said their findings provide some of the strongest evidence to date that legalization leads to increased use.  

They decided to focus on twins because it made it easier to control outside factors. Twins share the same genes, community norms and parental influences.

“This is the first study to confirm that the association between legal cannabis and increased use holds within families in genetically identical individuals,” said co-author John Hewitt, a professor in the Department of Psychology and Neuroscience at CU Boulder.

Marijuana is illegal in Minnesota except for edibles, which contain no more than five milligrams of THC.

Though the study showed that people are using marijuana more in states where recreational use is legal, researchers noted that these kinds of results may not be all bad because, they say, increased use may lead to less alcohol abuse. More than 141 million Americans live in a state where recreational pot is legal.