Study: Pot habit changes the brain

• Study of long-term marijuana users finds they have smaller decision-making area of brain


• Chronic marijuana users had an IQ 5 points lower than those who did not use


• Some scientists say this study shows marijuana is not "a harmless drug"

(CNN) -- Using marijuana at an early age could have long-term consequences on your brain and it may even lower your IQ, according to a new study in the Proceedings of the National Academy of Sciences.

Researchers found that compared to nonusers, people who smoked marijuana starting as early as age 14 have less brain volume, or gray matter, in the orbitofrontal cortex. That's the area in the front of your brain that helps you make decisions.

"The younger the individual started using, the more pronounced the changes," said Dr. Francesca Filbey, the study's principal investigator and associate professor at the School of Behavioral and Brain Sciences at the University of Texas at Dallas. "Adolescence is when the brain starts maturing and making itself more adult-like, so any exposure to toxic substances can set the course for how your brain ends up."

Public perceptions about pot have come a long way, from the dire warnings of "Reefer Madness" to growing acceptance of medical marijuana to the legalization of recreational weed use.

On July 27, the New York Times published "High Time: An Editorial Series on Marijuana Legalization," which called for the federal government to repeal its ban on marijuana.

Matt Figi's 7-year-old daughter Charlotte was once severely ill. But a special strain of medical marijuana known as Charlotte's Web, which was named after the girl early in her treatment, has significantly reduced her seizures. On July 28, Rep. Scott Perry, R-Pennsylvania, introduced a three-page bill that would amend the Controlled Substances Act -- the federal law that criminalizes marijuana -- to exempt plants like Charlotte's Web that have an extremely low percentage of THC, the chemical that makes users high.

While politicians and supporters look on, New York Governor Andrew Cuomo signs a ceremonial bill to establish a medical marijuana program in New York, on July 7, 2014. New York is the 23rd U.S. state to authorize medical marijuana.

In April, Maryland became the 18th state to decriminalize marijuana possession. Research published by the Pew Research Center in February showed 54% of Americans support legalization of marijuana.

Sean Azzariti, an Iraq war veteran and marijuana activist, becomes the first person to legally purchase recreational marijuana in Colorado on January 1. Colorado was the first state in the nation to allow retail pot shops. "It's huge," Azzariti said. "It hasn't even sunk in how big this is yet."

Members of a crowd numbering tens of thousands smoke and listen to live music at the Denver 420 Rally on April 20. Annual festivals celebrating marijuana are held around the world on April 20, a counterculture holiday.

A man smokes a joint during the official opening night of Club 64, a marijuana social club in Denver, on New Year's Eve 2012. Voters in Colorado and Washington state passed referendums to legalize recreational marijuana on November 6, 2012.

People light up near the Space Needle in Seattle after the law legalizing the recreational use of marijuana went into effect in Washington on December 6, 2012.

Nutrient products are placed on shelves in the weGrow marijuana cultivation supply store during its grand opening on March 30, 2012, in Washington, D.C. The store is a one-stop-shop for supplies and training to grow plants indoors, except for the actual marijuana plants or seeds. Legislation was enacted in 2010 authorizing the establishment of regulated medical marijuana dispensaries in the nation's capital.

Marijuana activist Steve DeAngelo wears a "Yes on Prop 19" button as he speaks during a news conference in Oakland, California, on October 12, 2010, to bring attention to the state measure to legalize marijuana for recreational purposes in California. Voters rejected the proposal.

Sonja Gibbins walks through her growing warehouse in Fort Collins, Colorado, on April 19, 2010. Since the state approved medical marijuana in 2000, Colorado has seen a boom in marijuana dispensaries, trade shows and related businesses. So far 20 states and the District of Columbia have made smoking marijuana for medical purposes legal.

A patient prepares to smoke at home in Portland, Maine, on October 22, 2009, a decade after the state approved a medical marijuana referendum.

Coffeeshop Blue Sky worker Jon Sarro, left, shows a customer different strains of medical marijuana on July 22, 2009, in Oakland, California. Voters in the city approved a measure during a vote-by-mail special election for a new tax on sales of medicinal marijuana at cannabis dispensaries.

Medicinal marijuana patient Angel Raich wipes her eyes during a press conference on March 14, 2007, in Oakland, California. The 9th circuit U.S. Court of Appeals in San Francisco ruled that 41-year-old Raich, who used medicinal marijuana to curb pain from a brain tumor as well as other ailments, did not have the legal right to claim medical necessity to avoid the possibility of prosecution under federal drug laws.

Different varieties of medical marijuana are seen at the Alternative Herbal Health Services cannabis dispensary in San Francisco on April 24, 2006. The Food and Drug Administration issued a controversial statement a week earlier rejecting the use of medical marijuana, declaring that there is no scientific evidence supporting use of the drug for medical treatment.

People in New York gather for a pro-cannabis rally on May 4, 2002. That same day, almost 200 similar events took place around the world to advocate for marijuana legalization. It was dubbed the "Million Marijuana March."

Dennis Peron takes notes during a phone interview while Gary Johnson lights up at the Proposition 215 headquarters in San Francisco on October 11, 1996. The ballot measure was approved when voters went to the polls in November, allowing medical marijuana in California.

A television ad aired in 1996 by Republican presidential candidate Bob Dole's campaign included footage from a 1992 MTV interview of a laughing President Clinton saying he would inhale marijuana if given the chance to relive his college days.

President George H. Bush holds up a copy of the National Drug Control Strategy during a meeting in the Oval Office on September 5, 1989. In a televised address to the nation, Bush asked Americans to join the war on drugs.

Robert Randall smokes marijuana that was prescribed to treat his glaucoma in 1988. He became the first legal medical marijuana patient in modern America after winning a landmark case in 1976.

First lady Nancy Reagan participates in a drug education class at Island Park Elementary School on Mercer Island, Washington, on February 14, 1984. She later recalled, "A little girl raised her hand and said, 'Mrs. Reagan, what do you do if somebody offers you drugs?' And I said, 'Well, you just say no.' And there it was born." She became known for her involvement in the "Just Say No" campaign.

President Jimmy Carter, with his special assistant for health issues, Dr. Peter Bourne, beside him, talks to reporters at the White House about his drug abuse control message to Congress on August 2, 1977. Among other things, he called for the elimination of all federal criminal penalties for the possession of up to one ounce of marijuana.

Panel members of the National Commission on Marijuana and Drug Abuse attend a hearing In Denver on January 10, 1972. From left, Dr. J. Thomas Ungerleider, psychiatrist; Michael R. Sonnenreich, commission executive director; Raymond P. Shafer, commission chairman; Mitchell Ware, Chicago attorney; Charles O. Galvin, Dallas law school dean. The commission's findings favored ending marijuana prohibition and adopting other methods to discourage use, but the Nixon administration refused to implement its recommendations.

Protesters wade in the Reflecting Pool at the National Mall in Washington during the "Honor America Day Smoke-In" thrown by marijuana activists in response to the official "Honor America Day" rally organized by President Nixon supporters at the Lincoln Memorial on July 4, 1970.

Marijuana reform was the Life magazine cover story in October 1969. The banner read: "At least 12 million Americans have now tried it. Are penalties too severe? Should it be legalized?"

Police dogs trained to smell out hidden marijuana examine U.S. soldiers' luggage at the airport during the Vietnam War in 1969. Drug use was widespread during the war.

People share a joint during a 1969 concert in Portland, Oregon. In 1973, Oregon became the first state to decriminalize cannabis.

Marijuana use became more widespread in the 1960s, reflecting the rising counterculture movement.

Research scientist Dr. Reese T. Jones, right, adjusts the electrodes monitoring a volunteer's brain response to sound during an experiment in 1969 that used a controlled dosage of marijuana. The tests were conducted at the Langley Porter Institute at the University of California, San Francisco.

U.S. Customs agents track the nationwide marijuana market during Operation Intercept, an anti-drug measure announced by President Nixon in 1969. The initiative intended to keep Mexican marijuana from entering the United States.

Members of the Grateful Dead talk with reporters from their home in San Francisco on October 5, 1967. The band was protesting being arrested for marijuana possession.

A woman buys ready-rolled marijuana cigarettes from a dealer at her door circa 1955.

Even after Congress cracked down on marijuana in 1937, farmers were encouraged to grow the crop for rope, sails and parachutes during World War II. The "Hemp for Victory" film was released in 1942 by the U.S. Department of Agriculture.

Marijuana cigarettes are hidden in a book circa 1940. Congress passed the Marijuana Tax Act in 1937, effectively criminalizing the drug.

A poster advertises the 1936 scare film "Reefer Madness," which described marijuana as a "violent narcotic" that first renders "sudden, violent, uncontrollable laughter" on its users before "dangerous hallucinations" and then "acts of shocking violence ... ending often in incurable insanity."

Harry Anslinger was named commissioner of the Federal Bureau of Narcotics when it was established in 1930. While arguing for marijuana prohibition, he played on Americans' fear of crime and foreigners. He spun tales of people driven to insanity or murder after ingesting the drug and spoke of the 2 to 3 tons of grass being produced in Mexico. "This, the Mexicans make into cigarettes, which they sell at two for 25 cents, mostly to white high school students," Anslinger told Congress.

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

History of marijuana in America

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Photos: History of marijuana in America

Researchers also found increased brain connectivity in chronic users. Connectivity, when different parts of the brain connect to each other, is important for adaptive learning abilities. It also helps your mind make associations. This wiring of the brain starts to deteriorate with chronic marijuana use.

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Colorado's booming marijuana industry

"Too much or too little of anything isn't good. There needs to be an equal balance," said Filbey.

There were 48 marijuana users enrolled in this study. All started smoking between age 14 and 30. The average age of the person enrolled in the study was 18. On average they used marijuana three times a day. Most said they had been using it for 10 years, although some had been smoking pot for three decades.

Scientists compared this group to a group of 62 nonusers of the same basic age and gender. All gave urine samples. All had an MRI scan and all went through IQ testing.

Filbey said the people who regularly used marijuana had IQ's that were five points lower, on average, than the nonusers in the study, although there is no definitive proof that marijuana alone was to blame for the lower IQ.

"While our study does not conclusively address whether any or all of the brain changes are a direct consequence of marijuana use, these effects do suggest that these changes are related to age of onset and duration of use," Filbey said.

Dr. Susan Weiss, associate director for Scientific Affairs at the National Institute on Drug Abuse said the study provides more strong evidence about the dangers of marijuana.

"This is a complex and interesting study that adds to the growing body of evidence that heavy marijuana use, particularly at a young age, is linked to significant adverse brain changes," said Weiss. "This study showed that the orbitofrontal cortex, an area involved in reward, decision making and motivation, was smaller in heavy users and that other brain circuits were enhanced, likely to compensate for the diminished function in that region. Further prospective studies are needed to clarify this, but these mounting scientific findings certainly challenge the widespread belief that marijuana is a harmless drug."

The National Institute on Drug Abuse helped fund the study.

Mason Tvert, director of communications for the Marijuana Policy Project, said marijuana use does not cause IQ loss.

"Once again, researchers have failed to find any conclusive evidence that marijuana use causes mental health problems. The researchers note their findings are nonconclusive, that they might be skewed by other factors, and that effects, if any, could be temporary, Tvert said. "The study doesn't justify keeping marijuana illegal, nor does it say anything about making it legal. There remains no doubt that marijuana is far less harmful than alcohol to the brain and to the rest of the body. The possibility that marijuana might have some harm for some people -- but might not -- is not a good reason to keep arresting and punishing hundreds of thousands of adults simply for using it."

Filbey next plans to do long-term observational studies with people who do not use marijuana to see if there are underlying factors like pre-existing conditions before exposure to THC, the psychoactive ingredient in cannabis, that could account for some of these effects.