Teens Don't Smoke More Pot After Medical Marijuana Laws Passed, Study Finds

New research has cast serious doubts on the argument that legalization of medical marijuana would lead to more widespread use among teenagers.

The study, which was published Tuesday by Columbia University researchers in the The Lancet Psychiatry, examined marijuana use among more than a million teenagers over 24 years.

The researchers found no discernible impact in the 21 states that had legalized the drug for medical use. “The risk of marijuana use in states before passing medical marijuana laws did not differ significantly from the risk after medical marijuana laws were passed,” the co-authors wrote.

While researchers observed no discernible change after the laws were passed, they did find drug use rates were generally higher in states that had legalized marijuana. “State-level risk factors other than medical marijuana laws could contribute to both marijuana use and the passage of medical marijuana laws, and such factors warrant investigation,” the authors concluded.

Go Inside the Harvest of Colorado's Most Controversial Marijuana Strain

Charlotte's Web grows on the Stanley brother's farm near Wray, Colo. on Sept. 22, 2014. The Stanley Brothers have developed a popular strain of cannabis that has been found to be helpful in reducing seizures in some children. Charlotte's Web is high in a compound called cannabidiol (CBD) and low in tetrahydrocannabinol (THC) the compound that causes a high.

Matt Nager for TIME

Charlotte's Web grows on the Stanley brother's farm near Wray, Colo. on Sept. 22, 2014.

Matt Nager for TIME

From left: Zachary Sobol, Michael Atchley, and Jared Stanley walk to the farm to prepare for harvest of Charlotte's Web near Wray, Colo. on Sept. 22, 2014.

Matt Nager for TIME

Rows of Charlotte's Web await harvest at the Stanley brother's farm near Wray, Colo. on Sept. 22, 2014.

Matt Nager for TIME

Jared Stanley helps in the harvest of Charlotte's Web on the Stanley brother's farm near Wray, Colo. on Sept. 22, 2014.

Matt Nager for TIME

Colin Sparks searches for seeds during the harvest of Charlotte's Web on the Stanley brother's Charlotte's Web farm near Wray, Colo. on Sept. 22, 2014.

Matt Nager for TIME

Discarded leaves of Charlotte's Web at a farm near Wray, Colo. on Sept. 22, 2014.

Matt Nager for TIME

Tim Knight helps in the harvest of Charlotte's Web on the Stanley brother's farm near Wray, Colo. on Sept. 22, 2014.

Matt Nager for TIME

Rows of Charlotte's Web await travel to a drying facility after being harvested on a farm near Wray, Colo. on Sept. 22, 2014.

Matt Nager for TIME

Zachary Sobol catches a ride on a trailer to the Stanley brother's farm during harvest of Charlotte's Web near Wray, Colo. on Sept. 22, 2014.

Matt Nager for TIME

Rows of Charlotte's Web await travel to a drying facility after being harvested from a farm near Wray, Colo. on Sept. 22, 2014.

Matt Nager for TIME

One of the Stanley brother's greenhouses growing cannabis near Wray, Colo. on Sept. 22, 2014.

Matt Nager for TIME

Zachary Sobol hangs rows of Charlotte's Web to dry after harvest in Wray, Colo. on Sept. 22, 2014.

Matt Nager for TIME

Penn Mattison, left, and Zachary Sobol, right, hang rows of Charlotte's Web to dry after being harvested from a farm near Wray, Colo. on Sept. 22, 2014.

Matt Nager for TIME

The Stanley brothers' new company laboratory in Boulder, Colo. on Sept. 23, 2014.

Matt Nager for TIME

A petri dish full of cannabis explants await transfer and transplanting at the Stanley brothers' lab in Boulder, Colo. on Sept. 23, 2014.

Matt Nager for TIME

Molecular plant biologist and lab manager Bear Reel awaits the cooling of agar to help induce rooting of transplanted cannabis plants at the Stanley brothers' company laboratory in Boulder, Colo. on Sept. 23, 2014.

Matt Nager for TIME

The lab notebook of molecular plant biologist and lab manager Bear Reel at the Stanley brothers' company laboratory in Boulder, Colo. on Sept. 23, 2014.

Matt Nager for TIME

A flask of agar cools before explants of hemp are transplanted to help induce rooting and new growth at the Stanley brothers' company laboratory in in Boulder, Colo. on Sept. 23, 2014.

Matt Nager for TIME

Tissue cutter technician Meg Regan holds a vial of explants before sanitizing and transplanting at the Stanley brothers' laboratory in Boulder, Colo. on Sept. 23, 2014.

Matt Nager for TIME

1 of 20

Advertisement

Contact us at editors@time.com.