As America Inhales, Scientists Raise Health Concerns

Marijuana is going mainstream. So far, 23 states have legalized medical use of the drug or effectively decriminalized it. Ohio recently voted against legalization, but another 17 states will consider the issue next year. As laws and societal mores around marijuana are rewritten, public health scientists at the Mailman School are taking a close look at a range of issues, from who is using it and how widely to its long-term consequences.

Epidemiology professor Deborah Hasin has written more than 350 papers on the epidemiology of drug and alcohol use disorders. In October, she published a study in JAMA Psychiatry finding marijuana use among adults more than doubled between 2001 and 2012. The numbers of people diagnosed as abusing the drug or dependent on it also climbed, reaching nearly 7 million, or nearly three in ten users. Was legalization of marijuana for medical purposes a factor? Among one group, at least, it wasn’t. A study of teenagers, published by Hasin in Lancet Psychiatry, found teen use of pot was elevated in states with medical marijuana laws, but because the rates of use were higher in these states before they even passed the laws, some other factor seems to be responsible for both the higher rates of use and the laws.

As director of the Substance Dependence Research Group at the New York State Psychiatric Institute, Hasin sees considerable evidence that using marijuana involves some risk. “Our studies show there are dangers from using marijuana,” she says. “Others have shown lasting impairments in brain functioning among adolescents who are heavy, regular users, while adults with marijuana use disorders show impairments across various areas of functioning.” 

Silvia Martins, associate professor of Epidemiology, points to a wealth of data on the health risks of regular marijuana use. Using it this way over the long-term is associated with reduced IQ, and with hallucinations, schizophrenia, and major depression, particularly if adults started using it heavily as teenagers. “Research shows that about one in eleven users can become addicted,” she says. “Regular and heavy marijuana use during the adolescent years can affect brain development and may reduce thinking, memory, and learning.”

Some of us are more attune to the risks than others. A study by Martins published in Drug and Alcohol Dependence earlier this year found women were twice as likely to see regular use of cannabis as potentially harmful, although that number had dropped from 59 percent in 2002 to 27 percent in 2012.

What Is the Evidence for Medical Marijuana?

Three-quarters of Americans favor using marijuana for medicinal purposes. Many in the medical community too favor its use for pain, as muscle relaxer, appetite enhancer, and for other reasons. Yet there has been very little careful research to back up this and other potential upsides. “We see segments on the news about children with epilepsy showing tremendous improvement from taking the drug,” says Hasin, a professor of Epidemiology. “Yet while it does help some, it could harm others, and we still need rigorous studies and data to guide our decisions about medical marijuana.”

One significant hurdle to research: marijuana is still classified as a Schedule I drug. This could change. Recently presidential hopeful Hillary Clinton echoed the sentiment of the American Medical Association by saying she would like to see marijuana reclassified so it can be more easily studied. “I want to move from Schedule 1 to Schedule 2 so researchers can research what's the best way to use it, dosage, and how it works with other medications," she said.

Driving High

It’s well known that alcohol and automobiles are a deadly combination. According to the Centers for Disease Control, almost 30 people in the United States die in motor vehicle crashes that involve an alcohol-impaired driver every day. What about pot? While driving under the influence of marijuana is illegal no matter what state you live in, growing numbers of marijuana users are getting behind the wheel.

In an analysis of toxicology reports from fatal car accidents published in the American Journal of Epidemiology, Guohua Li, found that one in eight drivers tested positive for the drug—up three-fold from a decade ago. A study published in the journal Accident Analysis & Prevention, found that relative to drivers who tested positive for neither alcohol nor drugs, the odds of a fatal crash climbed 13-fold for drivers testing for alcohol alone, but 24 times for those positive for both alcohol and marijuana. Whether or not the driver was high was unknown—marijuana lingers in the system for days—but it does point to the fact that the driver uses marijuana. In the future Li says, a breathalyzer-type device might provide more accurate information on intoxication. 

But the notion that alcohol is more dangerous than marijuana should be subjected to rigorous scrutiny and requires important qualification, argues Li, a professor of Epidemiology. “Although alcohol is more addictive and more impairing to cognitive functions than marijuana, moderate alcohol consumption may confer significant health benefits,” he says. Whether marijuana has a similar upside remains to be seen. And there is always potential for its misuse. Says Li, “There is no such thing as safe substance abuse, regardless of the drugs involved.”