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The recreational use of cannabis is illegal in the Jewish state, but for the past 10 years its therapeutic use has not only been permitted but also encouraged. Last year, doctors prescribed the herb to about 25,000 patients suffering from cancer, epilepsy, post-traumatic stress and degenerative diseases. The purpose is not to cure them but to alleviate their symptoms. Forbidden to export its cannabis plants, Israel is concentrating instead on marketing its agronomic, medical and technological expertise in the hope of becoming a world hub in the field.
 / AFP / JACK GUEZ        (Photo credit should read JACK GUEZ/AFP/Getty Images)
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An Israeli agricultural engineer inspects marijuana plants at the BOL (Breath Of Life) Pharma greenhouse in the country's second-largest medical cannabis plantation, near Kfar Pines in northern Israel, on March 9, 2016. The recreational use of cannabis is illegal in the Jewish state, but for the past 10 years its therapeutic use has not only been permitted but also encouraged. Last year, doctors prescribed the herb to about 25,000 patients suffering from cancer, epilepsy, post-traumatic stress and degenerative diseases. The purpose is not to cure them but to alleviate their symptoms. Forbidden to export its cannabis plants, Israel is concentrating instead on marketing its agronomic, medical and technological expertise in the hope of becoming a world hub in the field. / AFP / JACK GUEZ (Photo credit should read JACK GUEZ/AFP/Getty Images)
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GO WITH AFP STORY by Desiree Martin A picture taken on April 12, 2013 shows plants of marijuana at the plantation of the Sibaratas Med Can association in Mogan on the southwest coast of the island of Gran Canaria. The plants grow from cuttings for approximately two months and then blossom before being harvested, dried, stored in jars for a month and later processed to be consumed on site. Spanish law prohibits the possession of soft drugs like cannabis in public and its growth to be sold for profit is illegal. But the law does tolerate growing cannabis for personal use and its consumption in private. Dozens of private marijuana smoking clubs operate across Spain that take advantage of this legal loophole that serve cannabis users who do not want to get their drugs from the streets. AFP PHOTO / DESIREE MARTIN (Photo credit should read DESIREE MARTIN/AFP/Getty Images)
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(CNN) —  

Marijuana use among young people in the United States overall has climbed in recent years, but a new paper suggests that in states where recreational marijuana has been legalized, marijuana use among youth may actually be falling.

Laws that legalized recreational marijuana were associated with an 8% drop in the number of high schoolers who said they used marijuana in the last 30 days, and a 9% drop in the number who said they’d used at least 10 times in the last 30 days, according to the paper published in the medical journal JAMA Pediatrics on Monday.

“Just to be clear we found no effect on teen use following legalization for medical purposes, but evidence of a possible reduction in use following legalization for recreational purposes,” said Mark Anderson, an associate professor at Montana State University in Bozeman, Montana, who was first author of the paper.

“Because our study is based on more policy variation than prior work, we view our estimates as the most credible to date in the literature,” he said.

The paper involved analyzing data, from 1993 to 2017, on about 1.4 million high school students in the United States from the US Centers for Disease Control and Prevention’s annual national Youth Risk Behavior Surveys.

The researchers took a close look at self-reported marijuana use in the surveys among the students as well as survey responses in areas where medical or recreational marijuana was legalized.

The researchers examined the responses before and after the marijuana laws were implemented.

The data showed that marijuana use among high schoolers was not statistically associated with medical marijuana laws, but there was a link with recreational marijuana laws.

The paper had some limitations, including that only an association was found in the study – not a causal relationship – and more research is needed to determine why this association exists.

“Because many recreational marijuana laws have been passed so recently, we do observe limited post-treatment data for some of these states,” Anderson said. “In a few years, it would make sense to update our estimates as more data become available.”

The new study appears to contradict some separate state-level studies that suggest marijuana use among teens remains unchanged – instead of declining – following legalization, said Bonnie Halpern-Felsher, professor of pediatrics in Stanford University’s Division of Adolescent Medicine in Palo Alto, California, who was not involved in the new paper.

For instance, a 2018 report from the Colorado Division of Criminal Justice Office of Research and Statistics found that the proportion of high school students in the state who said they used marijuana ever in their lifetime or in the past 30 days remained statistically unchanged from 2005 to 2017. Colorado legalized the adult use of recreational marijuana in 2014.

When it comes to the new paper, “I think the big question is why,” Halpern-Felsher said. “Why are they seeing in this national dataset decreases – pretty significant decreases – when other studies are finding no difference?”

The researchers wrote in the paper that one possible explanation could be that in states where recreational marijuana is legal, “it is more difficult for teenagers to obtain marijuana as drug dealers are replaced by licensed dispensaries that require proof of age.”

Halpern-Felsher called that “a good point.”

“Maybe now because of having legalization, you don’t have the street sales anymore,” she said. “So dispensaries, we would hope, would be better at carding and checking for age verification.”

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Meanwhile on the national front, the overall prevalence of marijuana-only use among youth in the United States since the early 1990s increased from 0.6% in 1991 to 6.3% in 2017, according to a study published in the American Journal of Public Health on Wednesday.

“The other question is, are youth getting the message about the fact that using marijuana during adolescence is more harmful because of their brain development?” Halpern-Felsher said. “Given the legalization, we need more education around marijuana or cannabis use for youth and we don’t really have a lot of education.”