The biggest myths about marijuana—debunked by an addiction expert

Everything in moderation.
Everything in moderation.
Image: Reuters/Mark Blinch
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The march of marijuana legalization continues, and so do the questions about its effect on the health of smokers. Kevin Hill, an addiction psychiatrist at McLean Hospital in Harvard Medical School and author of Marijuana: The Unbiased Truth about the World’s Most Popular Weed, recently took to Reddit to answer questions from the public. Quartz has condensed and edited the highlights of the discussion.

What medical uses of marijuana are backed by evidence?

The two commercially available cannabinoids are FDA-approved for nausea and appetite stimulation. Beyond that, I think there is strong evidence supporting the use of marijuana or cannabinoids for chronic pain, neuropathic pain, and spasticity associated with multiple sclerosis.

What are the downsides of using marijuana? How often do people get addicted?

Most who use marijuana do not become addicted to it. Published data say that 9% of adults and 17% of young people who use it become addicted.

How do you diagnose marijuana addiction? What are the risks of withdrawal?

Usually there are problems in work, school, or relationships. For a family member, teacher, or coach, you have to have a good sense of what is normal for a person and be able to tell if things are normal any longer. Have they stopped doing the things they normally do? Is their mood different? These types of things.

Marijuana can affect the brain like other addictive substances by causing surges in certain chemicals, like dopamine, in the brain. The release of these chemicals is pleasurable and reinforcing—this makes it more likely that people will decide to use again. Marijuana addiction is both psychological and physical. People who really like to use marijuana may overdo it to the detriment of other important areas of their lives. They may rely upon using as a key coping mechanism to deal with stress in their life.

It can be physically addictive as well—if you are using daily, multiple times a day. The withdrawal symptoms—anxiety, irritability, difficulty sleeping—make it more likely that someone will continue to use. Importantly, these withdrawal symptoms are not life-threatening. Alcohol withdrawal can cause seizures that can be fatal.

While marijuana increases likelihood of respiratory infections like bronchitis, there are no long-term studies linking it to cancer at this point. Marijuana, on the whole, is not as dangerous as alcohol, which is probably not as dangerous as opioids. However, this does not mean that marijuana is not potentially dangerous.

Does inhaling marijuana have different risks from eating it?

The risks are mostly associated with what’s in marijuana, not the form it is consumed. So the risks associated with edibles are more due to the fact that the onset of action is longer and people unwittingly take higher doses than they intend to if they do not feel the effects quickly.

Is there a marijuana drug test?

I am not aware of a drug-test kit. Generally, marijuana will cause a positive urine test about 4 hours after use.

Is marijuana getting more potent?

Potency has increased dramatically. Average THC content—which is the active substance in marijuana—in 1960s was 3-4%. Latest published data puts potency at 13%.

Where do you stand on legalization of marijuana?

Arguments for legalized marijuana include freedom of choice for adults, ability to raise tax revenue, and decrease the number of marijuana-related arrests. Against legalization arguments include: increased use could increase addiction, alcohol and tobacco companies could target certain groups, and risk of compromising driving safety.

I am in favor of legalized recreational marijuana largely because I think adults should be allowed to do with their bodies and to their bodies what they choose, so long as it does not hurt others.

I want to emphasize, though, that in many states, like Massachusetts, that will have legalized marijuana on the ballot soon, the real question is no longer who is in favor and who is not, but rather, if it gets passed, what should the laws look like. More and more states will legalize marijuana, so we need to work hard to craft policy that gives people what the want while limiting risk.

What is the most dangerous marijuana myth?

The most dangerous myth: “Marijuana is harmless.” It’s not harmless. It is not as dangerous as opioids, for example, but while marijuana may not be as bad as opioids, it still can be dangerous.

Most researchers agree that early, regular use of marijuana—young people below 25 whose brains are developing—is a bad idea. Major negative effects of long-term use include cognitive difficulties, worsening anxiety, worsening depression, and increased likelihood of expressing a psychotic disorder (not causing one).