Twice As Many Americans Follow Marijuana Smoke 'Toward the Riff Filled Land'

If you ever wondered how three separate "Harold and Kumar" stoner movies got made, scholars may have found the answer. According to an article published in JAMA Psychiatry, the number of American adults who used marijuana more than doubled between 2001 and 2013, leaping from 4.1 to 9.5 percent. Researchers gathered the data by comparing thousands of responses to the "National Epidemiologic Survey on Alcohol and Related Conditions" from 2001-2002 and 2012-2013.

Their most troublesome conclusion found an increase in marijuana use disorders, with more than 6.8 million Americans affected. What's a "marijuana use disorder"? Well, the DSM-IV (the fourth edition of the "Diagnostic and Statistical Manual of Mental Disorders," if you're not into the whole brevity thing) basically classifies it as marijuana abuse or dependence. Bummer, man.

While nearly three out of every 10 marijuana users (an estimated 2.8 percent of the U.S. adult population) dealt with abuse or dependence in 2012-2013, there isn't cause for alarm just yet. The rise was likely due to the overall increase in people using marijuana, including new users. In fact, among existing marijuana users there was actually a decline in addiction and dependence.

So why are there so many more adults smoking pot? The study suggests it's because U.S. laws and attitudes toward marijuana are more lenient now. Twenty-three states currently have medical marijuana laws, while four have also legalized it for recreational use. So perhaps less "fear and loathing" leads to more bong rips.

The study also reported increased marijuana use in specific demographics: women, black individuals, Hispanic individuals, those living in the American South and those middle-aged or older. 

Another bummer? As people age, chronic marijuana use can hasten the loss of neurons in the hippocampus region of their brain. Another study published in March of this year found that teens who smoke marijuana daily for three years or more may have an abnormally shaped hippocampus. We've covered this further in the BrainStuff video above on how marijuana affects memory, because it turns out these brain deformations seem to be connected to poor performance on memory tests. The shape of the hippocampus actually becomes more abnormal the longer people use marijuana chronically. Even after stopping their marijuana use for more than two years, the abnormalities don't seem to go away either.

The authors of the JAMA Psychiatry study suggest this rise in marijuana use requires more public education about its potential risk for addiction. As with alcohol though, not everyone who uses it becomes an addict. Still, it's important to recognize that increased use in the population does seem connected to the growth of those experiencing addiction and dependence.