“It is hard for most to be objective about cannabis. Some say it is the greatest thing ever, others say if you use you are doomed. Neither is true. I encourage everyone to be open to the idea that the real answers are somewhere in the middle.”

kevin hill

Kevin Hill, MD


These are the words of Kevin Hill, MD, an addiction psychiatrist at McLean Hospital in Massachusetts. In 2015, he published the book Marijuana: The Unbiased Truth about the World’s Most Popular Weed and has made it a professional priority to translate the current state of marijuana research into information that the public can actually use.

For example, you can find him on the website Reddit, where he’s conducted two recent AMA’s (Ask Me Anything) that allow regular folks from all over the world to ask him questions about marijuana. As you can imagine, he gets all sorts of questions. Like:

What do you think would happen if you have someone receive an IV of pure THC over an extended period of time?

He has no idea.


In the meantime, the National Institute on Drug Abuse hosted its first-ever Marijuana Research Summit earlier this week. The purpose of the summit was to consolidate the research community’s knowledge on three questions about marijuana: 1) What do we know? 2) How do we know what we think we know? and 3) What do we still need to know?

Like Hill, federal leaders have decided it’s time to get past emotional arguments about marijuana and focus on facts. In fact, it’s overdue.

How do I know we’re overdue? Here’s an example. As I listened to neuroscientists at the NIDA summit describe the body’s endocannabinoid system (which is affected by marijuana use), I thought it might be helpful to watch a video overview of the system. You know, try and get a handle on the neurotransmitters and enzymes and ligands the scientists rattled off so fast and furious. Every single video I found on YouTube about the endocannabinoid system was published by a marijuana advocate like the420TeaParty or Decriminalise It

Here’s another example. Hop on Pinterest and search #marijuana. There, you’ll find cute marijuana cupcake recipes and fancy glass pipes, but that’s to be expected. More importantly, you’ll find authoritative-looking infographics about cannabis strains, medical marijuana, and drug policy created not by scientists or clinicians, but by everyday people with a pro-marijuana agenda. Where’s the science? How does the public find accurate information about marijuana?

The conversation has already begun. We’re quite late to the party.


Here’s a quick rundown of information shared at the NIDA summit about marijuana and cannabinoids. Although there were plenty of interesting discussions about marijuana’s therapeutic value, this list refers to the health risks of marijuana use, including addiction.

We need to look at strains and how they vary in their effects on health. Past research has neglected this area.

THC is just one of more than 80 cannabinoids in marijuana, but it’s the one that gets you high, so marijuana plants have been bred to produce it. In recent decades, the THC content in marijuana has climbed from 3-4% to 18 or 21%. The THC content in high-potency marijuana products like concentrated hash oil can reach 80%. Although the body of research literature on marijuana use goes back several decades, we have extremely limited knowledge on comparative risks and benefits of various strains, many of which are available for consumers to buy legally in some states.

Marijuana addiction is a real thing.

Just like alcohol, tobacco, and every other mood-altering drug we know of, some people get addicted marijuana, although most who use it do not. There is ample evidence of marijuana’s addictive potential when you look at it from any angle imaginable: there’s a marijuana withdrawal syndrome, people diagnosed with cannabis use disorder meet the same criteria as people diagnosed with other substance use disorders, and a substantial number of people admitted to addiction treatment facilities are there because of marijuana use.

We don’t yet know of “low risk” levels of marijuana use, as we do with alcohol.

We don’t have nearly enough population-level data on patterns of use and the mental and physical health effects associated with it to determine “low-risk” guidelines for marijuana use. In his Reddit AMA last month, Hill said, “Hard to set a limit. Just like alcohol, no concrete limit fits everyone. We tend to think of problematic use as being 4x a week or more — this is a general guide. There could be instances where 4x a week or more may not be a problem, but it would be a red flag for a clinician like me.”

Regular cannabis use seems to affect cognitive function, especially if use begins in adolescence.

Two presenters at the NIDA Summit shared research that suggests that persistent cannabis use can affect cognitive function–and those effects may not be reversible. Madeline Meier summarized a well-known prospective longitudinal study with New Zealanders that tracked participants over a period of more than 20 years. In it, people who met the diagnostic criteria for cannabis use disorder at several times in their life actually lost IQ points over time. Susan Tapert showed that adolescents who use marijuana regularly tend to score lower on tests of memory and attention. However, after several weeks of abstinence, these differences shrink.

Cannabis use can contribute to first-episode psychosis for a small but significant portion of the population. This risk is higher if use is daily or if the product is high-potency synthetic marijuana.

Cannabis exacerbates symptoms of pre-existing psychosis or genetic susceptibility to schizophrenia. There is strong evidence that the use of marijuana–especially daily marijuana use or high-potency marijuana product use–is associated with first-episode psychosis in young people. Although it’s not clear whether cannabis use causes psychosis or simply provokes it earlier in life, we know that the earlier the onset of a psychotic episode, the worse health outcomes we see.

Said Hill, “It is sad when marijuana use triggers a psychotic break in young people. We are left to wonder if such a break would have occurred without cannabis.”

As with treatment of other substance use disorders, behavioral treatments for cannabis addiction can be successful, but there’s lots of room for improvement.

At the NIDA summit, the aptly-named Alan Budney presented his lab’s cannabis use disorder research findings. Their results showed that, as with other substance use disorders, behavioral therapies like Motivational Enhancement Therapy, Cognitive Behavioral Therapy, and Contingency Management (otherwise known as Motivational Incentives) is effective for some people. Even with the best combination of behavioral therapies, he found that only 30% of participants with cannabis addiction were abstinent after 12 months. However, abstinence is not the only treatment goal worth achieving.

“Total abstinence is a great goal, but one can significantly reduce marijuana use and see tremendous clinical benefit,” Hill wrote on Reddit last month. “I have worked with many patients who used 4x a day, everyday, for years and were able to cut down to a couple times a week. They feel pretty good about that type of result and I do, too.”

Pharmacological treatments are being developed, but we don’t have any pinned down just yet.

One promising medication is the hormone pregenolone, which may block the high created by THC, similar to the way naltrexone can block opiate effects.


ONDCP Michael Botticelli

ONDCP Director Michael Botticelli

Michael Botticelli, Director of the White House ONDCP, spoke briefly in support of marijuana research at the NIDA summit. He emphasized the importance of shaping policy with science. And he commended American scientists for their global leadership on drug research.

He’d just come from the 59th UN Commission on Narcotic Drugs in Vienna. There, he was reminded of what vital contributions American researchers make to the world’s knowledge base on drugs and addiction. We are world leaders in this area and it’s something to be proud of, he said.

It was funny to be reminded that America leads the world in drug research and that we still have so much to learn about marijuana and health. Which is not to say we know nothing.

For example, we know quite a bit about what happens to our endocannabinoid system when we use marijuana. Like this:

That’s not to shabby. But we don’t have a full picture of the risks of marijuana use. We’re just sketching them out now. And we have failed to effectively communicate to the public that there are risks, even if we don’t fully understand them.

Madeline Meier, whose landmark study shows an association between persistent marijuana use and lower IQ, said at the NIDA summit, “When I talk to adolescents about this, they just don’t believe me.”

Kevin Hill echoed her concern on Reddit. “When I give talks,” he said, “I like the comparison between alcohol and marijuana. Most who use either don’t develop problems. As a society, though, we recognize the dangers of alcohol in a way that we do not for cannabis.”


Recorded video of the two-day NIDA Summit

Kevin Hill on Reddit

SBIRT for Adolescents, a free online course led by pediatrician Sharon Levy

Marijuana Lit by the National ATTC Network