Is marijuana dangerous? Should it be legal?

September 19th, 2013

A Q&A with addiction researcher Bernard Le Foll

Jenny Hall

A spate of politicians recently admitted to smoking marijuana, and the public, for the most part, shrugged its shoulders. With talk of decriminalization gaining momentum, we spoke to Dr. Bernard Le Foll about pot’s effect on the body and brain, and about the complex issues that surround the debate over legalization.

At U of T, Le Foll is a professor in the Departments of Family and Community Medicine, Pharmacology & Toxicology, Psychiatry and the Institute of Medical Sciences. At the Centre for Addiction and Mental Health (CAMH), he is head of the Alcohol Research and Treatment Clinic and of the Translational Addiction Research Laboratory at the Campbell Family Mental Health Research Institute. His clinical activity is centered on alcohol and tobacco dependence. The goal of his research is to improve treatment of drug addiction. He has received scientific prizes and awards from the Canadian Institutes for Health Research, the National Institutes of Health – National Institute of Drug Abuse, the French Academy of Medicine, the American College for Neuropsychopharmacology, the College on Problems on Drug Dependence, the Society for Research on Nicotine and Tobacco, NARSAD, Pfizer, OPGRC, the Ontario Lung Association and the Heart and Stroke Foundation.

[Since this interview was originally published on Sept. 19, 2013, the information above was revised to reflect Professor Le Foll’s research record.] 

Marijuana use seems to be increasingly socially acceptable. Several politicians recently admitted that they have smoked pot. What’s your take on this?

Politicians are gradually catching up with the reality of use in society. It’s a drug that is widely used. It’s also a drug that is used for medical purposes. There has been pressure from the public to recognize those facts. But on the other hand, it’s a drug that has a clear addictive potential and has many negative effects.

The conventional wisdom is that marijuana is not addictive.

It’s clear that marijuana is addictive. The addictive potential is probably higher than most people believe. Five to seven per cent of users will develop dependence over time after repeated exposure, but more than a third of users will have difficulty controlling their use at some point in their lives. If you are chronically exposed to marijuana, when you attempt to stop, you can develop withdrawal symptoms, and you will have difficulty maintaining abstinence.

And I think it’s important to say that if you develop cannabis use disorder there is currently no pharmacological treatment to help you. This is different from alcohol, tobacco or opioid dependence, where we have medications to help. We are doing research at CAMH on the possibility of developing a substitution therapy for cannabis. Take the analogy of smoking: if you want to quit, you can take a nicotine replacement. If you’re a heroin user you can get a medication like methadone. We have the idea that the same approach can be used for cannabis, and we are evaluating the possibility of using Sativex, a buccal spray that contains THC and cannabidiol, which are the two main components of cannabis smoke. Sativex is currently on the market as a multiple sclerosis treatment.

Earlier you said marijuana has many negative effects. What are they?

Marijuana is almost always smoked. Therefore, users are exposed to the same type of health-related consequences as smoking tobacco, which might mean cardiovascular impact, respiratory impact and so on. There is also a probability of developing cancer due to exposure.

The difficulty is dissociating what is due to cannabis versus what is due to tobacco because those two substances are very often used simultaneously. But there is agreement by most physicians and experts in the field that it’s very likely that you’re exposed to at least the same health risk as tobacco.

But what is different from tobacco is that on top of those effects, with cannabis you have clear psychiatric effects. There is a very clear association with risk of developing schizophrenia and psychosis, and there are suggestions that it may also facilitate other psychiatric disorders such as depression and anxiety. Clear cognitive effects and decrease of general motivation are seen in daily users. There was also a study published a few months ago showing negative impact on IQ after exposure.

For this reason, allowing easy access to cannabis may result in increasing negative consequences. But that is true for all drugs of abuse. The more you open the door to their use, the more people will develop negative consequences. There is nothing specific to cannabis here.

Can we make a distinction between an occasional user versus a regular user in terms of these negative outcomes?

It is clear that vascular and respiratory effects are likely to occur even with limited exposure. For psychiatric consequences, we don’t know what the threshold is. This is all highly dependent on your genetic makeup. This means that it’s very likely that some people may develop, even with very low exposure, some psychiatric effects. Other people can take larger quantities and not develop negative consequences. Right now we cannot predict who will develop negative psychiatric consequences and who won’t.

This is why the debate is complex. Proponents of use say they have used for a long time and everything is fine. But this does not necessarily account for long term health effects that may occur years later. In addition, the absence of psychiatric effects may be true for one person, but another person could develop a psychiatric disorder after much less exposure.

So do I infer that you’re not personally in favour of legalization?

I believe we have to look at this in an objective manner. We currently have tobacco and alcohol on the market. Tobacco is killing 50 per cent of its users. Nine per cent of the Ontario population has alcohol use disorder, and another nine per cent uses alcohol in a risky manner—bingeing, for example. So right now you have between 15 and 20 per cent of the Ontario population having trouble controlling their alcohol use. There is an indication here that if you open the door widely to addictive drugs, there can be large-scale negative consequences. Also, we already have some form of legalization with the medical marijuana program, under which users can use cannabis for medical reasons. So there is already an experience in Canada of allowing use under specific circumstances.

On the other hand, we know that we will likely not get rid of cannabis in society by banning it. Keeping marijuana illegal creates specific negative effects: some people lose trust in the system of regulation because they believe it’s unfair that cannabis is illegal (as compared nicotine and alcohol, for example) and then they put themselves outside of the legal system to get it. This puts users in contact with dealers who may then offer other types of drugs. More importantly, lots of money goes into the trade of cannabis. Putting it into the illegal market provides billions of dollars per year into organized crime. Legalizing it could allow the government to control the situation, and it could have a positive financial impact. Another potential advantage of legalization would be to put users into contact with the support they need. A large majority of regular users have mental health problems, and a large number of those may benefit from connecting with the health care system.

So, taking all this into consideration, I believe we have to think of new systems to regulate access to cannabis. In my view, such a system should ultimately aim at reducing the negative impact of cannabis on individuals and society. We do have to be careful because legalization without proper regulation can lead to increased negative consequences.

Can you talk a little more about how medical use of marijuana works?

Our body relies on an internal cannabinoid system to function properly. Under normal circumstances, cannabinoid substances are synthetized in multiple organs in our body, such as the brain, and are involved in multiple functions such as brain and metabolic regulation. Cannabis or other drugs target this system by acting on receptors, which are like targets on our cells for those substances. By modulating those targets, marijuana is likely producing beneficial effects such as pain control in some people. Unfortunately, inhaling cannabis smoke is not a good way to deliver the cannabinoid drug to patients because they get exposed to the negative consequences of inhaling smoke.

But does it always have to be smoked?

Most users smoke, but some users take cannabis orally, or they use a vaporizer. Those are likely less harmful way of using it. It is important for every user to assess the balance between the benefit and the risk of their consumption. Discussion with a health care provider can be useful for that. There are also pharmaceutical alternatives coming—some companies are putting cannabinoid drugs into pills or spray. The advantage of this is that we will be able to assess the benefit and risk more clearly for these drug preparations. It is currently a very active area of research.


A joint. Photo by kt_sarah,