Medicinal cannabis: the pros and cons

Q&A: There is evidence cannabis can help to manage chronic pain but there are side-effects

Cannabis is in the news these days, with campaigns underway on both sides of the Border for its legalisation for medicinal use.

Mothers such as Corkwoman Vera Twomey, who has marched to Dublin in support of access to legal medicinal cannabis to treat her child's epilepsy, have been to the forefront of the campaign.

The decision on legalisation will be made by the Oireachtas, whose health committee began on Wednesday its scrutiny of a Bill put forward by Solidarity/PBP TD Gino Kenny on the issue.

So what are the pros and cons of medicinal cannabis?


Does it work?

That depends on who you talk to. A report by the Health Protection Regulatory Authority (HPRA) found an absence of scientific data to demonstrate the effectiveness of medicinal cannabis. In summary, it said there is "at best, a moderate benefit for cannabis in a small number of conditions and conflicting evidence, or no evidence at all, in a large number of other medical conditions".

“The effectiveness and safety of cannabis in large numbers of medical conditions is simply not proven,” it concluded.

In contrast, a UK report by Prof Michael Barnes concluded there was considerable literature demonstrating the effectiveness of cannabis products in a number of important conditions.

There is good evidence for the use of cannabis in managing chronic pain; spasticity; nausea and vomiting; and the management of anxiety, he found.

He said the evidence was moderate in relation to sleep disorders; fibromyalgia; post traumatic stress disorder; and Parkinson’s. There was limited evidence of effectiveness in using cannabis to treat agitation in dementia and epilepsy, and no evidence “so far” supporting its use for cancer, headaches or depression.

Are there side-effects?

All medicines have side effects; the issue is whether their benefits, for particular patients, outweigh these side effects.

The potential side-effects of recreational use of cannabis are well-known. They include impaired short-term memory and coordination, psychosis, addiction and altered brain development. “There is compelling evidence linking cannabis use in adolescence with the development of psychosis in later life,” the HPRA report points out.

The Barnes report says there is probably a link between cannabis use and schizophrenia among those who start using it at an early age and have a genetic predisposition to psychosis. It also quotes a 9 per cent dependency rate and advises against the smoking of cannabis on health grounds.

He summarises: “The evidence for cognitive impairment in long term users is not clear but it is wise to be cautious in prescribing cannabis to younger people, given the possible susceptibility of the developing brain”.

But aren’t these the potential harms of recreational use - what about medicinal use of cannabis?

This is a more difficult question to answer. For a start, the medicinal use of cannabis is fairly new, largely ad hoc and for the most part unregulated, so little or no data has been gathered. The HPRA says the monitoring of side effects is “limited or non-existent”.

Obviously, the exposure of patients to harm increases if they take a product without regard to proper dosing or if they go on to become a recreational user. The wider use of cannabis for medicinal purposes is likely to lead to its wider availability generally.

Doesn’t it depend on what parts of the cannabis plant people are consuming?

Yes - assuming they know what they are taking.

Cannabis contains more than 100 plant cannabinoids - biologically active parts of the plant that bind to receptors in the body to produce wide-ranging effects. It is thought they mimic the effects of the body’s own cannabinoids, known as endocannabinoids.

The two cannabiniods of greatest interest to researchers are cannabidiol (CBD) and tetrahydrocanabinol (THC).

The treatment of these substances under law is very different; THC, because it delivers the symptoms of cannabis such as hallucinations and delirium, is a controlled drug under the Misuse of Drugs Act and therefore illegal. In contrast, CBD has no psychotropic impact, and is not illegal.

Families seeking to access medicinal cannabis have found it relatively easy to source products such as CBD oil, though at €300 a bottle it is not cheap. These are marketed as food supplements as to make medical claims for what is an unregulated product would be illegal.

The first licensed CBD oil product is likely to be authorised internationally this year. For some, CBD-only products suffice, but other users want stronger products that also contain THC.

Have any products been developed?

A variety of cannabis-containing products are in development, and one - Sativex - has already been licensed in Ireland. Sativex, which contains both CBD and THC and is used by multiple sclerosis patients, is not available free under the medical card scheme because no agreement on price was reached with its manufacturer.

What have other countries done?

Rules governing access to medicinal cannabis are being liberalised in many parts of the world. Of 40 countries surveyed by the HPRA, 16 countries do not have any access programmes, nine have programmes for exceptional use similar to that advised by the HPRA, and three countries have wider access programmes. Despite evident misgivings, it suggested Ireland establish a limited access programme, only for patients with specified medical conditions that have failed to respond to all other treatments.

Minister for Health Simon Harris has given the go-ahead to this access programme, which will cover resistant MS, intractable nausea and vomiting associated with chemotherapy and severe epilepsy. The scheme will not cover chronic pain after the HPRA found its causes were too diverse, the condition was too common and other treatments were available.

But isn’t medicinal cannabis going to be legalised anyway?

That impression gained ground after the Government unexpectedly allowed Gino Kenny's Bill on the issue to proceed to committee stage. While only one TD - GP and health committee chairman Michael Harty - voted against it at first stage, it is not expected the Bill will proceed further without major amendment.

And in the interim?

The Minister is moving forward with an access programme as suggested by the HPRA. An expert committee has been set up to design this programme.

Does that mean families cannot for now obtain medicinal cannabis?

No, doctors can get the Minister’s permission to give products to their patients, and one child is being treated in this way after a licence was issued for a product containing THC. However, other applications have been refused, apparently because the doctors are concerned over the lack of long-term data on the effectiveness and safety of cannabis-containing products.

Paul Cullen

Paul Cullen

Paul Cullen is a former heath editor of The Irish Times.