COLUMBUS, Ohio- Several studies have shown that frequent use of marijuana may hurt the brains of teenagers and young adults.

Smoking marijuana just once a week can have a “significant” negative effect on the brains of teenagers and young adults, including cognitive decline, poor attention and memory, and decreased IQ, according to psychologists discussing the health implications of legalizing marijuana at the American Psychological Association’s 122nd Annual Convention.

A 2012 study found that 6.5 percent of high school seniors reported smoking marijuana daily, up from 2.4 percent in 1993. Additionally, 31 percent of young adults between the ages of 18 and 25 reported using marijuana in the last month. A 2013 study of more than 17,000 teenagers in Montana found that marijuana use among teenagers was higher in counties where larger numbers of people voted to legalize medical marijuana in 2004. In addition, teens in counties with more votes for the legalization of medical marijuana perceived marijuana use to be less risky.

Morgan Fox with the Marijuana Policy Project believes the way to curb that increase would be to legalize marijuana. He points to Colorado, where he claims usage rates are down.

"Whether it's because of more stringent identification at these stores or because of elimination of the elicit market or because simply that teenagers don't think marijuana is cool any more because it's legal," Fox said.

Brain imaging studies of regular marijuana users have shown significant changes in their brain structure, particularly among adolescents, according to Dr. Krista Lisdahl, director of the brain imaging and neuropsychology lab at the University of Wisconsin-Milwaukee.

"We know especially teens that use it at an earlier age that it really can cause some problems and science is really showing that," said Tony Coder with the Drug-Free Action Alliance in Ohio.

Brain experts are urging lawmakers to consider regulating the level of tetrahydrocannabinol, or THC, in marijuana. Today's marijuana plants are being grown to produce more of the chemical than plants grown decades ago.

Fox argues that higher THC levels could actually be a benefit since people using marijuana for medical purposes would not need to smoke as much.

Coder worries that legalizing marijuana will lead to commercialization.

"Commercialization means that there's going to be more pot in the community," he said.

Fox disagrees. He'd like to see marijuana treated more like alcohol and tobacco. He thinks that's the best way to get usage rates in check among young people.

"We need to take it out of the hands of drug dealers and put it in the hands of legitimate businesses that are regulated and have an incentive not to sell to minors," he said.

Coder says the drug is dangerous and should remain illegal. He often hears the argument that no one has ever died from using marijuana.

"Fine they aren't dying by overdose, but there are so many issues, just like smoking, where the long-term effects are really what is driving the safety or the non-safety of this drug," Coder said.