Once a state legalizes recreational marijuana, residents are more likely to start using it, even those below the legal age of 21, according to a new study.

HealthDay reports researchers at the University of California, San Diego studied more than 6,900 youths ages 12 to 20, as well as almost 15,000 adults, using a national database. Participants were from four states with legal recreational marijuana (California, Massachusetts, Nevada and Maine); 11 states with medical marijuana; and 17 states that prohibit marijuana use.

“Our findings provide useful information to policymakers and public health practitioners interested in understanding the consequences of legalizing recreational cannabis,” lead researcher Yuyan Shi said in a news release. “It’s especially concerning that increased cannabis use occurs among young people because of the detrimental health effects associated with cannabis use at a young age, including impaired respiratory function, cardiovascular disease, and adverse effects on mental health.”