Medical cannabis is the new kid on the block. It’s the latest in a long line of medications that claim to treat a multitude of health problems, but what is the evidence for its use? Does it hold the potential to help patients with intractable pain, refractory seizures, or severe mental health conditions? Or are they the new opiates or benzodiazepines.


Cannabinoids are not new. They’ve been around millions of years and we have millions inside of us right now. These are endogenous cannabinoids that act on the body across a range of systems. They are involved in the neurological system, endocrine system, immune system, mood, pain receptors etc.

Herbal cannabis – the plant – contains variable amounts of CBD and THC. Used for countless years to supposed good effect by either chewing, distilling or smoking. Also used for recreational use.

Synthetic (man-made) cannabinoids, like THC containing Nabilone or Sativex. Mainly used for treating chemotherapy-induced intractable nausea or refractory seizures but are licensed for use in spasticity conditions like MS also.


Medical cannabis contains 2 main ingredients. THC and CBD. CBD is the non-psychoactive component wheres THC is what is supposed to cause the potential psychogenic properties and possible addiction.

The products available at the moment contain varying amounts of these ingredients, but they come in 3 main categories:

  1. High CBD, Low THC
  2. Medium CBD, Medium THC
  3. Low CBD, High THC.


Cannabis plants

Cannabis has been used for a long time to treat a multitude of conditions. Previously it was used solely in its plant form. The leaves were either chewed, ingested whole, put into other food products, distilled into a liquid form (oil) or smoked.

The use of recreational cannabis has long been a point of contention, especially the legal aspects. For those both for and against its legalisation, there has been much argument and lobbying. In recent years the landscape has changed and it seems it’s making headway in getting legalised. Many parts of the world have legalised cannabis but there are still many which have not.

Despite the issues with legality many have used it to treat their conditions, successfully they would say. I have certainly seen patients with metastatic cancer forego traditional palliative care in favour or cannabis with good effects and no particular side effects, but this is anecdotal.

Medical cannabis

Cannabis has the potential to treat many conditions. There are some guidelines available to doctors for its use which can be found on sites like DynaMed and Uptodate, although detailed prescribing information is lacking.

Typical uses include:

  • Cannabinoid spray or THC for spasticity conditions like Multiple-Sclerosis
  • Smoked cannabis or low dose THC for neuropathic pain
  • Cannabinoids for chemotherapy-induced nausea and vomiting


Unfortunately despite cannabis users and drug companies extolling the virtues of cannabis, the evidence remains weak. The fact is there just isn’t much evidence for its use, and the evidence we do have is not particularly robust.

Adverse effects

Not just do cannabis and cannabinoids have weak evidence for their use, they also carry potential side effects which limit their efficacy and effectiveness. Side effects include:

  1. Psychological effects
  2. Hallucinations
  3. Addiction
  4. Insomnia
  5. Psychosis
  6. Cognitive delay or impairment
  7. Cardiovascular damage (high blood pressure, high heart rate)
  8. Nausea and vomiting
  9. Chronic cough
  10. Respiratory problems

The likelihood of adverse effects is hard to judge. Just as hard as the appropriate dosing, mostly due to lack of data, however also due to the nature of these products. Unlike opiates for example which have a clearer dosing regimen, cannabis products are extremely individualised making guidelines for dosing extremely difficult to produce.

Cannabis vs Opiates / Benzodiazepines

When discussing cannabis products we cannot help but compare them to opioids and benzodiazepines (benzos). These drugs were hailed as the saviour to all of life’s troubles and were prescribed with gay abandon. We now have a world addicted to opiate medications and benzodiazepines.

Not through any fault of the doctors, they were just doing what they were advised. They simply did not know the potential dangers these medications had. Now we are much more careful, but the damage is done.

There is evidence however that cannabis can lower the burden of opioid addiction. In USA, in states with legalised cannabis, the authors observed an almost 25% reduction in opioid-related mortality, whilst after legalising medical marijuana there was a reduction in opioid-related deaths of around 20% in the first year.


There is a distinct lack of guidelines. As previously stated there are sites like DynaMed and UpToDate that try to collate the evidence as best they can to produce guidelines, but the fact is there is very little evidence to review. At best they can produce ‘weak evidence’ guidelines.

NICE in the UK has some of the most comprehensive guidelines available and even they state there is a distinct lack of evidence available and conclusions are difficult to draw.

We do not have robust guidelines in Australia and so prescribing information is often left to the individual drug companies to advise, which has the potential for conflict of interest.

Due to the lack of evidence, it is impossible to draw conclusions about the use of medical cannabis. It may be the solution that we have all been looking for, or it simply could be the next opioid crisis.


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