Dr. Claude Cyr is a palliative care doctor at the 51吃瓜网 Health Centre. An interest in the medical use of cannabis led him to his former position as an Associate Researcher for the , the world鈥檚 first research database on the use of cannabis for medical purposes. On Palliative Care McGill鈥檚 Continuing Professional Development Day (November 21st, 2025),听Dr. Cyr will discuss the potential of cannabis use in palliative care. In this interview, provides us with his insight ahead of his talk.
Vanessa Ruan (VR): What is the potential of cannabis in palliative care?
Dr. Claude Cyr (CC): I think the potential is enormous. Once you get used to managing and authorizing cannabinoid (components of cannabis) use in life-threatening illnesses, you realize that despite the current lack of evidence, there are many patients who derive multiple benefits from using it, such as the reduction of pain and anxiety.
VR: Wait, so cannabis can both reduce anxiety and induce euphoria?
CC: Yes! There's a U-shaped response for THC (see illustration), one of the major cannabinoids in cannabis. At sub-psychoactive doses (<2.5mg), it reduces pain and anxiety with little chance of perceiving the subjective effects. This is regarded as the psychoactive threshold. Above the psychoactive threshold, people perceive subjective effects, such as a bit of euphoria and relaxation. At a high dose, it may increase anxiety depending on your baseline endocannabinoid tone, and it may cause hypotension as well.
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VR: Is it possible to exploit the intoxicating effect of THC in palliative care?
CC: That is the most important question. In my opinion, cannabis was designed for palliative care. William O'Shaughnessy was a British physician in the 1800s who, while working in India, introduced cannabis to Western medicine. He gave cannabis tinctures to patients who were dying and remarked, "It strews the path to the tomb with flowers.鈥�
Cannabis allows people who are aware that they're dying to see that life is still worth living and to enjoy those little moments. At moderate doses, THC alters our salience attribution. It makes people pay attention to things that they didn't, and this gives a sense of novelty. Interestingly, THC also makes people easily distractible. That is not a good thing if you're driving. But if you're depressed and you鈥檙e obsessing over your cancer, and suddenly you're thinking鈥斺�渙h, what's that? That's a strange thing.鈥� Your salience network becomes a little activated, you start focusing on something else, and you forget about your cancer for about 10 minutes.
Moreover, most people feel time slows down when they're using THC. If my subjective perception of time slows down, it feels like I have more time than I thought I had. And if there's one thing that people who have cancer or terminal disease become obsessed with, it's the time that they have left. THC helps people to appreciate the time that they had, as it also enhances people鈥檚 senses and sociability: suddenly, you're not thinking about your cancer, you're having a conversation with somebody, and your coffee this morning tasted better than usual.
At high doses of THC, it produces psychedelic effects that are considered by many to be identical to psilocybin. Psilocybin was found to reduce anxiety in patients with advanced cancer because people have mystical experiences where they feel they are connecting with the universe. One patient, after his psilocybin session, said he realized that consciousness is not something that belongs just to him: 鈥渋t exists everywhere, and I'm part of that fabric. I know that when I'm going to die, consciousness will go on.鈥�
VR: Do you mean that one of the goals of palliative care is to bring about this cognitive change?
CC: I see the future of cannabis in palliative care as a stepping stone to get to this. One of the main issues that we have in palliative care and in oncology is existential distress. Death anxiety. When people realize that they're going to die, most of them do not take it well. We see this especially with our young patients, the 20-25-year-olds. They're completely stuck in their little bubble, disconnected from the world because they feel hopeless. However, when you ask them, 鈥淲hat are the most important things in your life?鈥�, it's usually their connections with other people. So, how do you get people out of that spiral of despair and continue to live a meaningful life while knowing that they have six months or a year to live? We don't know. We give antidepressants or tranquilizers to reduce the symptoms of distress and anxiety. It works.
VR: But it doesn鈥檛 change cognition.
CC: Exactly. We don't want to sedate these people. We could, and we often do because we have no choice, because people are in such distress and say, 鈥淚 don't want to feel this anymore.鈥� When you sedate them, well, now they really can鈥檛 enjoy their life because they鈥檙e just in bed all day.
Psilocybin does change cognition, but it is illegal. As mentioned, there have been studies that investigated psilocybin鈥檚 use in patients with advanced cancer and found that it significantly reduced patients鈥� death anxiety. However, psilocybin gives such an intense experience that research participants need multiple sessions to debrief and integrate the experience. Once they make sense of their experience, it's like shaking a snow globe: all the little snowflakes fall to the ground and land in a different place. Cannabis provides a glimpse of what this is. If you're giving low or moderate doses, your patient is not going to get a psychedelic experience like connecting to the universe or seeing demons, but they will understand that 鈥淚'm not losing my mind. For just about a couple of hours, I see things in life a bit differently.鈥� The angle changes. It鈥檚 like watching things through a prism. And this is what patients in palliative care need.
One of the things that people often don't realize is that it is not death that they鈥檙e afraid of. It is living. They鈥檙e afraid that something bad is going to happen when they continue living. But all the time that you're worrying, your time is ticking. Days and weeks and months are going by when you鈥檙e sitting here, twirling your thumbs, staring at the walls, and worrying. In this case, there's only one loser here. And that's you.
With THC, instead of putting a lid on their anxiety like sedatives do, we let it transcend and go to the other side: acceptance. It is the door that we need to open for people to get out of that rut of worrying about their mortality, so that they can continue living and have a bit of fun during the time that they can still function and think properly, still talk to their family and friends, still travel, et cetera.
VR: What are some contraindications that people need to consider when introducing cannabinoids in palliative care?
CC: In palliative care, there is one major contraindication, which, in my opinion, is still underappreciated. It is the fact that THC interacts with immune checkpoint inhibitors (immunotherapy) and may make them less effective. There are two studies showing that patients who use cannabis during their treatment had about a 30% lower response rate to immunotherapy, which was dramatic. Another study showed a similar trend but was questioned due to its method. Still, as a precaution, if you're a cancer patient and you're having immunotherapy, please consider the risks of using cannabis that are involved with your survival and your response to immunotherapy. Whether you have pain or anxiety, consider using something else to treat your symptoms. Immunotherapy is a revolution in oncology. It has dramatically increased survival in cancer patients over the last 10 to 15 years. But now we may not be getting as many benefits as we think we are because one out of every four of our patients is using cannabis during their treatment. This is two to three times higher than the rate of cannabis use in the general population. Among cancer patients who are using cannabis, one-third of them started using cannabis for the first time in their lives after they were diagnosed with cancer.听There are, of course, other contraindications, including having prior mental health problems such as being actively psychotic or a schizophrenic, but it is the interference with immunotherapy that worries me the most.
For more information on Dr. Cyr鈥檚 lecture and CPD Day, please visit the CPD Day webpage. Make sure you !