11 Key Findings From One Of The Most Comprehensive Reports Ever On The Health Effects Of Marijuana

The change in attitudes toward cannabis and in legal access to marijuana around the US over the past several years is staggering.

As of last fall, 57% of adults in the US said they thought marijuana should be legal, with only 37% taking the opposing view — which is essentially a reversal of the opinions held a decade ago.

And after November’s elections, 20% of Americans live in a state that has voted to legalize recreational use. Far more live in states with some access to medical marijuana.

But this obscures a crucial fact: From a scientific perspective, there’s still a ton we don’t know about cannabis.

A massive report released today by the National Academies of Sciences, Engineering, and Medicine gives one of the most comprehensive looks — and certainly the most up-to-date — at exactly what we know about the science of cannabis. The committee behind the report, representing top universities around the country, considered more than 10,000 studies for its analysis, from which it was able to draw nearly 100 conclusions.

In large part, the report reveals how much we still have to learn, but it’s still surprising to see how much we know about certain health effects of cannabis.

This summation was sorely needed, as is more research on the topic.

“The policy has outpaced science, and it’s really too bad,” Staci Gruber, an associate professor of psychiatry at Harvard Medical School and director of the Marijuana Investigations for Neuroscientific Discovery program at McLean Hospital, told Business Insider in an interview last week, several days before we saw the report.

“As a scientist, I think the goal is always to try very hard to get to the findings and to be able to disseminate those findings so that we can make good decisions grounded in science,” Gruber said. Cannabis “has been around for thousands of years; it’s not like we just made it in a lab.”

Having good research is essential so that we know “how best we can use it, what are the safest ways, and what are the real risks,” she added.

Surprising findings on cancer, mental health, and more

Before we dive into the findings, there are two quick things to keep in mind.
First, the language in the report is designed to say exactly how much we know — and don’t know — about a certain effect. Terms like “conclusive evidence” mean we have enough data to make a firm conclusion; terms like “limited evidence” mean there’s still significant uncertainty, even if there are good studies supporting an idea; and different degrees of certainty fall between these levels. For many things, there’s still insufficient data to really say anything positive or negative about cannabis.

• to experience chronic bronchitis and that stopping smoking was likely to improve these conditions. There’s not enough evidence to say that that cannabis does or doesn’t increase the risk for respiratory conditions like asthma.
• There was limited evidence that smoking marijuana could have some anti-inflammatory effects.
• Substantial evidence suggests a link between prenatal cannabis exposure (when a pregnant woman uses marijuana) and lower birth weight, and there was limited evidence suggesting that this use could increase pregnancy complications and increase the risk that a baby would have to spend time in the neonatal intensive care unit.
• In terms of mental health, substantial evidence shows an increased risk of developing schizophrenia among frequent users, something that studies have shown is a particular concern for people at risk for schizophrenia in the first place. There was also moderate evidence that cannabis use is connected to a small increased risk for depression and an increased risk for social anxiety disorder.
• Limited evidence showed a connection between cannabis use and impaired academic achievement, something that has been shown to be especially true for people who begin smoking regularly during adolescence (which has also been shown to increase the risk for problematic use).
• One of the most interesting and perhaps most important conclusions of the report is that far more research on cannabis is needed. Importantly, in most cases, saying cannabis was connected to an increased risk doesn’t mean marijuana use caused that risk.
• And it’s hard to conduct research on marijuana right now. The report says that’s largely because of regulatory barriers, including marijuana’s Schedule I classification by the Drug Enforcement Administration and the fact that researchers often can’t access the same sorts of marijuana that people actually use. Even in states where it’s legal to buy marijuana, federal regulations prevent researchers from using that same product.

 

Without the research, it’s hard to say how policymakers should best support legalization efforts — to say how educational programs or mental health institutions should adapt to support any changes, for example.

“If I had one wish, it would be that the policymakers really sat down with scientists and mental health practitioners” as they enact any of these new policies, Krista Lisdahl, an associate professor of psychology and director of the Brain Imaging and Neuropsychology Lab at the University of Wisconsin at Milwaukee, told Business Insider in an interview shortly before we could review this report.

It’s important to know what works, what doesn’t, and what needs to be studied more. This report does a lot to show what we’ve learned in recent years, but it also shows just how much more we need to learn.

In studying cannabis, “we’re not really after the good or the bad — we’re after the truth,” Gruber said.