Laura Murphy : Cannabis for Pain : Navigating the Weeds

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Laura Murphy, Pharmacy Clinical Site Leader at University Health Network

Opiates and Pain Management

Ontario is facing an opioid crisis that is driven, in part, by prescribing practices. This session will discuss practical ways for clinicians to help patients manage pain. It will include strategies to safely deprescribe and discuss the impact of both medical and recreational cannabis use.

Descriptive Transcript

So I have nothing to disclose. No commercial or financial interests. I am an employee of the University Health Network. I’m a member of Project Echo Ontario pain hub team. And I’m also a member of the pharmacists mentoring in addiction and pain, which is an offshoot of the medical mentoring, addiction and pain. I’d like to acknowledge some of the contributors of slides to this presentation. This is certainly a topic that a lot of people have interest in and something that I continue to learn about every day from my patients and colleagues.

And really I think what we can achieve today is navigating some of these practicalities around cannabis for pain. So we have not only patients that we’ve provided medical authorizations to in the chronic pain clinic, but many more patients who come to us and tell us they’re already using cannabis for pain. And they come to us with interesting questions related to safety, related to titration, and I think these questions really come out of a huge swirling amount of information around them, related to cannabis for pain, coming from lots of different sources, just like many other options for management for pain, but I don’t want to discount experiences from other people and their own lifetime experience with cannabis, because they bring that with them and I think it’s our job as clinicians not only to decide if it’s appropriate, but also to help guide, you know what’s reasonable information to consider when they’re making their own choice around cannabis for pain.

So there is a body of evidence that continues to grow, we’re very excited. So there have been five meta-analysis and systemic systematic reviews in the last decade, but even more recently than that. This one looked at several studies with vaporized or smoked cannabis. So this was primarily herbal cannabis that they looked at, and they did find that at low doses it did help with refractory neuropathic pain. Then of course more recently there was a Cochrane review that came out, and like many of the other meta-analysis or systematic reviews that included cannabis based medicines or cannabinoids. So some of the pharmaceutical products that we have and in contrast this study, when they kind of slice and dice the evidence a different way, found that the harms actually outweighed the benefits for cannabinoid based medicines for chronic neuropathic pain. So I think we do need more information a lot of these studies had many many limitations.

So just a bit of animation here I’ll just skip right through. So the Cochrane review really considered some of the CNS adverse effects and some of the psychiatric adverse effects, to make that decision around the fact that the harms that weighed the benefits. I think what we can gather from the evidence at this point is that cannabis has a lot of promise, and may be beneficial for some individuals in reducing their pain. What we don’t know yet if it helps them to improve their function at this point with related to their chronic pain. And we do need to monitor for some of these adverse effects. Most of the studies that have been done have been in various doses, so we really don’t know at specific doses what types of adverse effects we could expect, especially with the rising THC percentages that we see in products on the market. And then there are the less common adverse effects to consider.

Things like cannabis use disorder, that we really should be screening for, and also other rare adverse effects. Cannabis withdrawal syndrome is something we’re very interested in the hospital, and we’re expecting we may be seeing this more often, but without screening for it we have very little ways of knowing, especially when people coming in with poly substance use, whether or not they’re withdrawing from cannabis. So I think many hospitals around the country are interested in developing protocols for management of withdrawal. If you are considering providing authorization for cannabis, it’s very important to identify if there any contraindications and certainly age less than 25 years because of the continuing development of the brain at that point, is something very important to consider. Personal or strong family history of psychosis also important, and also a person’s substance use to consider their risk.

And if you are considering authorizing, there is a medical document available from Health Canada that prompts for all the required information, but the access to cannabis for medical purpose regulation continues to provide people access through licensed producers, or for people to register with Health Canada to either produce their own cannabis or to designate someone else to grow cannabis for them. I’ve included the possession limits here. So it is higher if somebody has a medical authorization as opposed to if somebody’s buying it through like the Ontario cannabis store. But really all that’s required on the medical document at this point is a license number a period of use for up to one year and a daily quantity of dried cannabis or the equivalent and then really the person can self-select with the licensed producer or grow whatever strains or really percentages in terms of the components that they would like.

And the cost is quite high for many of our chronic pain patients compared to other things that are covered, or other things they may pay out-of-pocket for. There are some private plans that are starting to provide coverage for some of this, especially with extended coverage. And I think that will start to change quite rapidly. So cannabis is not just one thing, as I’ve alluded to it’s many many active compounds, over 550 chemical compounds in fact, and we know very little about most of them. The ones we do know mostly about is THC and CBD. And in terms of how to dose these different percentages we know very little about dosing CBD, it mostly comes from anecdotal evidence, and basically starting low and going very slow, but we are finding that people are needing much much higher doses than we ever anticipated to get any sort of benefit.

With THC there’s an even stronger emphasis on starting very low and going slow, and that meta-analysis I showed earlier found that at very low doses of THC, found that at very low doses of THC. So you can see 1.9 milligrams to 34 milligrams per day teach to your equivalent people were seeing a small benefit of about 30% of pain reduction. The route is also very important to consider in terms of pharmacokinetics, people who are used to using vape, vaporized or inhaled or smoked, they’re used to getting in effect in seconds, and so now we see people switching to oils and they don’t see in effect for 30 to 60 minutes. They may take a second dose, a third dose, or edibles, also we see people having one, two, three gummy bears, whatever’s in those gummy bears, and then within two to four hours when those doses peak they’re finding themselves to be very euphoric, feeling very terrible and we see them presenting at the emerge, unfortunately, so it’s really important to educate people around this expectation for when the effect may have an onset, and as well the duration of effect, because for things like driving, operating heavy machinery, having to go into work, if something is lasting six to 12 hours and someone’s taking at bedtime at midnight they may still have residual effects the next day.

So what was interesting to me is that when they did a survey, many people feel like cannabis may impair their ability to drive and these are people using it for medical purposes, but like a third of people who are surveyed actually felt like it didn’t impair their ability to drive and some people said it depends and anecdotally that comes from responses like I think I can drive better when I use cannabis. So this piece around driving is really a key component, we’re starting to see commercials in the news and hopefully that perception will change over time. I think what’s really important for pharmacists, I know many of you are here today, but also any clinicians who are managing people with multiple comorbidities and polypharmacy are the pharmacokinetic interactions that cannabis has the potential for, given that it’s mediated through the sip 3A4, 2C9, 2C19 system. There have only been case reports of clinically significant drug interactions.

There was a case report cyclosporine as well. So in the transplant world this is a huge consideration, but for others we really only have pharmacokinetic data at this point, but I think there will be many more hopefully started to be reported. And then smoking itself of of course has an influence on Cip 1A2. So as people transition from smoking potentially to oils. We also need to consider that in terms of having an impact on their other medications that are medications that are metabolized through Cip 1A2. And then of course there are pharmacodynamic interactions. So one of the hugest questions I get from many patients referred to me because we work with them, related to their opioids is around opioids sparing effects. Like can cannabis replace my opioids? Can cannabis help me get off of my opioids?

So there is some promising preclinical data that saw that cannabis can reduce the use of morphine. In terms of clinical data we saw that it improved pain and sleep in people who were also using opioids, and in one case series they did find reduced opioid use with cannabis. So some people are using that as a modality. But I will just end on a note of caution. There’s also questions around abuse liability. So this study was published earlier this year, and although there wasn’t an increase in the use of cannabis with opioid there was an increase in terms of positive subjective effects of people’s oxycodone.

So because of the pathways that they’re interacting on, there is the potential that cannabis increases the liking of opioids for people so that may actually kind of fly in the face of trying to help people taper off of their opioids if that’s what their goal is. And so finally I’ll leave you with this slide about our patient Lucie. Just representative of many of the chronic pain patients that we see, and it’s just really important to remember that when we gather information from them that they’re using cannabis. That the cannabis you should be one of many modalities that they’re using to manage the chronic pain, and is just one element of their life, and just like the talk earlier, really shouldn’t stigmatize them. [Applause]