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Fact or Fiction

Marijuana-related claims proven, disputed, disproven in recent studies


Studies about pot's effects continue to evolve.
  • Studies about pot's effects continue to evolve.

As the marijuana industry grows, so too do the number of studies being conducted about its effects on users, including dental health, DNA, and teen usage rates and related behavioral problems.

The research is always evolving, so take these results with a grain of salt.

CLAIM: Smoking marijuana can cause your teeth to fall out.

FACT: Well, sort of. It's not the cannabis that's hurting gums, according to a study of 1,000 New Zealanders who smoked cannabis or tobacco for 20 years, but rather the smokers themselves, who are less likely to take care of their teeth than nonsmokers. The study found that cannabis users brush and floss their teeth less often, which can lead to periodontitis, a disease that affects gum tissue. If periodontitis isn't treated, teeth can become loose and fall out.

CLAIM: Marijuana mutates DNA.

FACT/FICTION: This one is a depending-on-who-you-talk-to kind of thing. Late last month, scientists from the University of Western Australia announced that using cannabis mutates DNA and leaves users more susceptible to diseases. They also claimed that the mutated DNA could be passed down to children, potentially causing slow cell growth in babies and poor development of a baby's organs and other body parts. The scientists also claimed that the mutated DNA could cause cancer to develop.

But earlier this month, marijuana researcher and board-certified neurologist Ethan Russo, also the founding editor of the Journal of Cannabis Therapeutics, told that the initial report was based on falsehoods.

"Cannabis is not mutagenic (productive of mutations in DNA), nor is it teratogenic (productive of birth defects) or carcinogenic (causative of cancer)," Russo said. "Countless animal studies and human ... studies support its relative safety in this regard."

CLAIM: Marijuana usage rates among teens are rising as more states legalize weed.

FICTION: According to researchers at Washington University School of Medicine in St. Louis, teen marijuana use (and marijuana-related behavioral problems) is actually dropping in the U.S.

The researchers reviewed responses to the National Survey on Drug Use and Health from more than 216,000 teens from 2002 to 2013. They found that in 2002, just over 16 percent of respondents used marijuana. In 2013, less than 14 percent used.

Likewise, the percentage of teens with cannabis use disorders fell from 4 to 3.

Legalization advocates are using results like these, and that of the 2015 Monitoring the Future survey, which also found a drop in the percentage of teens consuming marijuana, to fuel their argument that legalization doesn't negatively affect teens. ♦