Texas Doctor Warns Marijuana Lowers IQ, Damages Brain—Research Shows He's Wrong

This summer, Oklahomans will have the chance to vote whether or not they would like to legalize medical marijuana. Recently, an addiction psychiatrist from Texas spoke with the Oklahoma Medical Board about the dangers of this drug. However, his claim that marijuana lowers IQ seems to be debatable.

Dr. Harold Urschel is the chief medical strategist for EnterHealth, an addiction treatment program in Dallas. He spoke with the Oklahoma Medical Board, as well as local Oklahoma news channel KOCO News 5, about the dangers of marijuana. In light of the upcoming Oklahoma vote on whether or not to legalize medical marijuana, Urschel has warned residents of the Sooner State that the long-term risks of this drug are not worth the short-term relief, the news channel reported.

Related: Marijuana Legalization 2018: Which States Might Consider Cannabis Laws This Year?

"For teenagers, it decreases your IQ by eight points, which is a significant drop,” said Urschel in the KOCO News 5 clip. “It causes significant risk of heart attacks, lung cancer. Doubles your risk of stroke."

03_08_marijuana Marijuana plants are grown at Essence Vegas' 54,000-square-foot marijuana cultivation facility on July 6, 2017, in Las Vegas, Nevada. A claim that marijuana lowers a person's IQ is still debatable. Ethan Miller/Getty Images

Urschel is referring to a 2012 study that showed individuals who heavily smoked marijuana before the age of 18 had around an eight-point reduction in their IQ. The most important takeaway from this study seems to be the vulnerability of the young still developing the brain, Forbes reported. For example, similar studies have also shown that heavy alcohol use during adolescence can also lead to permanent brain damage and reduce memory. If marijuana is legalized in Oklahoma, only those aged 18 and older can have access to it. 

Related: Legalizing Marijuana Nationwide Would Create One Million Jobs, Study Says

For every study that suggests that marijuana lowers your IQ, there are several that show the opposite. The most recent of these, a twin study from 2016, studied the effects of marijuana on the IQ of identical twins, one of which was a habitual user and the other was not, over the course of 10 years. The conclusion was that there was absolutely no measurable link between marijuana use and lower IQ, Science Mag reported.

Dr. Bennet Davis, an addiction specialist and director of pain recovery at Arizona-based Sierra Tucson, told Newsweek that he was familiar with the research Urschel was referring to, but emphasized that the effect was found in teen brains, not adults. There is little research on marijuana’s effect on adult brains, and Davis said much of the lack of research is related to the drug’s current classification.

“It’s difficult to get NIH funding to study a drug that is illegal,” Davis said.

For this reason, we are in a catch 22—we do not know much about marijuana’s effects on the brain because it is illegal, but the drug remains illegal because we do not know much about its effect on the brain.

The association between marijuana use and IQ may still be up for debate, but the conclusion is clear for Urschel. “I believe the IQ change is real and based on the science that I’ve seen,” he told Newsweek.

In June, Oklahomans will vote to legalize the use and sale of medical marijuana for patients at least 18 and older.