Legalizing medical marijuana does not increase the use of the drug among adolescents, according to a recent study.

Researchers from Rhode Island Hospital found that states with medical marijuana laws did not see an increase in marijuana use in teens.

"Any time a state considers legalizing medical marijuana, there are concerns from the public about an increase in drug use among teens," Esther Choo, M.D., principal investigator and an attending physician in the department of emergency medicine at Rhode Island Hospital, said in a statement.

For the study, researchers compared 20 years worth of data from states with and without medical marijuana laws. They compared trends in self-reported adolescent marijuana use between states and found no increase in marijuana use that could be attributed to the law.

"This adds to a growing body of literature published over the past three years that is remarkably consistent in demonstrating that state medical marijuana policies do not have a downstream effect on adolescent drug use, as we feared they might," Choo said.

Medical marijuana is currently legal in 21 states and the District of Columbia.

The study also examined a nationally representative sample of high school students. The data showed that past-month marijuana use was common, at nearly 21 percent of the study population. However, there were no statistically significant differences in marijuana use before and after policy changes in any state pairing.

"Researchers should continue to monitor and measure marijuana use," Choo said. "But we hope that this information will provide some level of reassurance to policymakers, physicians, and parents about medical marijuana laws."

The findings were recently published online in advance of print in the Journal of Adolescent Health.

Founded in 1863, Rhode Island Hospital in Providence, R.I., is a private, not-for-profit hospital and is the principal teaching hospital of The Warren Alpert Medical School of Brown University.