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Cannabis and paediatric epilepsy – an expert answers your FAQs

An expert answers some frequently asked questions about the use of cannabis in paediatric epilepsy.



Dr Evan Lewis, a neurologist and founder of the Neurology Centre of Toronto (NCT), has treated over 500 patients with medicinal cannabis. Here he answers some frequently asked questions about cannabis in treating paediatric epilepsy.

In 2018 it was stories of children including Alfie Dingley, Billy Caldwell and the many other families affected by severe treatment-resistant epilepsy who joined the campaign, which led to the legalisation of medical cannabis in the UK. Yet today, almost five years on, access remains limited, with families still forced to fund prescriptions privately and few paediatric neurologists willing to prescribe. 

The real-world evidence for cannabis as a treatment for epilepsy has been steadily growing in recent years. One case series by researchers at Drug Science, showed seizures fell by an average of 86% among 10 children treated with whole plant cannabis. Analysis by the same researchers found that a child has a 96% chance of having a ‘significant reduction in seizures were they to be prescribed’ cannabis. This is far higher than any of the typically prescribed epilepsy medications. 

However, awareness and understanding of cannabis medicine among doctors remains low, which means many families are left to try and help their child on their own or relying on other parents through social media and support groups. 

Dr Evan Lewis is a neurologist and founder/medical director of the Neurology Centre of Toronto (NCT) with expertise in paediatric neurology and epilepsy having treated over 500 adult and paediatric patients with medicinal cannabis. 

As our epilepsy expert, he has helped us tackle some of the tricky topics parents may have to navigate when it comes to trying cannabis-based medicines for their child. Read on for his answers to some of the FAQs about cannabis and epilepsy.

Q: What do we know about why cannabinoids can be effective in treating epilepsy?

A: Cannabis has a unique mechanism compared to current available treatments and medicines. It works on the endocannabinoid system (ECS) and while some of the mechanisms and potential targets have been worked out, there’s a lot of research pending in terms of figuring out exactly how cannabinoids affect the ECS and how the ECS is involved in epilepsy. 

For instance, CBD has multiple targets and multiple effects and it appears that the cumulative effects of CBD tend to converge on a mechanism that reduces the excitability of neurons. Seizures are typically a consequence of a hyper-excitability and synchronicity of neurons. Another way to think about a seizure is uncontrolled electrical activity in the brain that the brain cannot suppress or turn off on its own. CBD through all its multiple different mechanisms, tends to cause the neurons to decrease this electrical activity. 

THC also has some fairly well worked out mechanisms, mainly its role at the CB1 receptor. This too, tends to reduce the activity or excitability of neurons in a different way than CBD does. 

When we put both CBD and THC together, what makes things even more interesting, is that CBD and THC appear to counteract each other. One way of conceptualising this is that both CBD and THC together may help to regulate or bring an otherwise dysregulated ECS into balance. Therefore, CBD and THC in various proportions may be able to reduce the excessive electrical activity in the brain which causes seizures.

So, in the end, it’s quite complicated and there’s still an enormous amount of research needed to properly understand exactly how the ECS works and its role in the manifestation of seizures.  

Q: Where can I get advice on dosing CBD?

A: There are a number of groups within the UK, such as Medcan Family Foundation and The Medical Cannabis Clinicians Society, who should be able to direct you to professionals who understand cannabis, and who can potentially provide guidance on dosage. There are also international experts like myself, and other cannabis practitioners in Canada in the US, where that experience has been developed over time and dosing protocols have been established. It’s important to note that if you were to contact an international physician, they would be unlikely to be able to give specific advice but they could certainly guide you to other local resources. The other thing I would say is look at what published research is out there, which can help provide information on dosing as well. Any of these routes should be able to, at least, point you in the right direction

Q: Will CBD bought over the counter (without a prescription) be effective for preventing seizures?

A: While I’m not saying the CBD itself would be ineffective, using over the counter CBD products without the guidance of a medical professional is a very unsafe practice.  

Safety is priority. The problem here is that one may not be able to be certain of the contents of an over-the-counter CBD-dominant oil. You might not know what you’re actually purchasing, and seizures could be made worse. Any kind of seizure management whatsoever should always be done under the guidance of a physician, this includes the management of seizures with CBD products or any kind of cannabinoid-based product. My preference would be with a neurologist who also has expertise in medical cannabis, and this is why more neurologists need to learn how to manage cannabis for their patients. 

I do understand, however, why families and patients might move towards purchasing CBD over the counter. If they don’t have another option and they don’t have practitioners who have knowledge or are willing to listen, then I can see how this would drive vulnerable individuals to seek treatment by any means possible. I would strongly, strongly caution patients and parents against this, though, and implore them not to give up on a search for an advocate or an expert in the field. I would also strongly recommend the regulators to implement a model in which these kinds of situations are prevented.

Q: Will my child experience any side effects from CBD and what should I look out for?

A: There have been various randomised control trials that have been done, especially with Epidiolex, which have shown that CBD in low doses is quite tolerable. As soon as one starts increasing the dose one has to be cautious regarding diarrhoea, decreased appetite and tiredness. These side effects are typically dose dependent, meaning the more you take the more likely you are to have them. 

In terms of long-term side effects for CBD, we have no idea, as there is no evidence for long term CBD side effects because we don’t have any data on that just yet. We have four to five year follow up data that’s been published and it looks like purified CBD products are safe and tolerable, but you do still have to be aware of the short term effects.

The other thing to always consider is drug-drug interactions. We know that CBD interacts with other drugs, including some epilepsy drugs and that’s another reason why parents should always talk to a practitioner with knowledge in cannabis rather than buying it over the counter.

Q: Is it safe to use oils containing THC in children with epilepsy? Can too much THC increase seizures?

A: There are several uncontrolled trials, by which we mean lacking the use of a placebo group, where children with epilepsy were exposed to certain amounts of THC, and from these we can glean a lot of data on safety in terms of dosing, especially in the context of CBD. We know that when THC is used in combination with CBD, it tends to ameliorate the unwanted side effects of THC. Unlike CBD, there have not been formalised trials that have explored the safety of THC in depth to the same degree. THC can have anti-seizure effects and the decision to add THC to any treatment plan ends up being a risk benefit decision at that time. There’s a fairly significant amount of data that can reassure experienced practitioners that THC can be relatively safe, given that risk benefit balance.

It’s important to recognise that we do not have any general short-term or long-term published data specifically on the use of THC in an appropriate and medically-supervised situation. The data showing long-term, adverse effects of THC all comes from recreational THC studies. There is a possibility that THC could increase seizures, but any of the cannabinoids have the potential to increase seizures at high enough doses and this is a question that needs to be answered.

We know at a preclinical level that THC has been found to be both anticonvulsant and pro-convulsant, so there’s certainly a risk there and from a personal clinical point of view I see THC both reduce seizures and decrease seizures similar to CBD. 

Q: Will THC affect my child’s development?

A: There is a risk that THC without the presence of other cannabinoids would affect your child’s development. We know that the long-term effects of recreational use of high amounts of THC frequently used over a long period of time can show changes in behaviour, mood, IQ and can cause structural changes in the brain. Will THC when used in a medically-supervised situation with dosing that aligns with evidence affect your child’s development? That we still do not know, and the same goes for CBD.

Whenever we make a decision as a practitioner or a parent or a patient, about utilising cannabis, it must be taken into consideration that we don’t know the long-term outcomes. We have to establish what’s going on for that individual at the time and if it is worth the risk of uncertainty to get seizures under control. There are many situations in which I believe that it is, given the amount of short to medium term data we have about development and about the safety and tolerability of THC and other cannabinoids.

Dr Evan Cole Lewis is a Neurologist and Clinical Neurophysiologist with expertise in paediatric neurology and epilepsy. He is the founder and medical director of the Neurology Centre of Toronto (NCT) and VP Psychedelic Neurology at Numinus. He is assistant professor with the Department of Paediatrics at the Hospital for Sick Children and the University of Toronto.


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