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There has been much written about this topic over the last few months, and I suspect I don't have anything new to add to the debate. However, reading the news coverage did prompt me to browse the medical literature for the latest research in an attempt to understand the potential benefits of this contentious substance.

Cannabis has been used medicinally in various forms for many centuries, at least as far back as Ancient Greece and China. Interestingly, even way back then, its benefits were mainly in the realm of pain relief, nausea, muscle spasm and joint inflammation – very similar to today. It was most commonly chewed rather than smoked.

Cannabis remained on the "medicines list" in the United States until the 1940s, and in the UK and parts of Europe until the 1970s. The main reason for its removal from medical use was the lack of ability to regulate it – the dose, quality and potential risks. Medical interest around its use was reignited in the 1980s, after reports surfaced of cannabis smokers with HIV, AIDS or cancer finding it an effective method of managing their pain, nausea and loss of appetite.

Natural cannabis contains a number of chemicals, known as cannabinoids. The psychoactive (or mind-altering) cannabinoid is known as THC (delta-9-tetrahydrocannabinol), but there are over 60 others.

Many of these cannabinoids have been successfully manufactured in labs, to enable scientists to work out exactly what their effects might be. To date, it appears that the most useful ones for medicinal purposes are likely to be THC and CBD (cannabidiol):

* THC increases appetite and reduces nausea. It is also thought to decrease pain, inflammation and muscle control problems. In the US, the FDA has approved 2 THC-medications for use to date. Its use is currently for patients with cancer, HIV and AIDS.

* CBD is a cannabinoid that does not affect the mind or behaviour. It is thought to be useful for pain, inflammation, seizure control, and possibly for treating mental illness and addictions.

Research into THC, CBD and other cannabinoids is continuing, and it is likely that further potential benefits will be revealed in the near future.

It is hoped that these drugs will be helpful for patients with multiple sclerosis, other neurological or muscle-wasting conditions, retractable epilepsy, and Alzheimer's disease. Cannabinoids cannot cure these diseases, but their effects could be life-changing for many patients.

One advantage that medical cannabis has over other traditional treatments is that it seems to provide a "broad-spectrum" effect – patients with HIV/AIDS report benefits in nausea, pain and joint aches, as well as improving appetite and reducing anxiety. To achieve these effects without cannabis would likely require a cocktail of medications, with potential drug interactions and a range of side-effects.

Patients with chronic or intractable pain may stand to benefit the most. Trials studying patients with a variety of painful conditions (including arthritis, trauma, neurological pain, migraines, advanced cancer) have shown that medicinal cannabis is effective, when other treatments have failed.

It is also thought to be safer than the standard first-line drugs – high doses of opiates and other medications can lead to morbidity and even death, but this is not a risk with cannabis. Pain relief from cannabis is immediate and easy for patients to titrate, and it has much fewer side-effects than other potent analgesics.

In neurological conditions such as multiple sclerosis, motor neurone disease and intractable epilepsy, cannabis treatment could create huge gains, largely because existing medications often have little or no effect. Smoked cannabis and synthetic compounds have been studied - both have been shown to reduce the severity and number of seizures for certain types of epilepsy, and to improve muscle spasm and mobility in multiple sclerosis.

So with all these possible benefits, why isn't medicinal cannabis available as yet on prescription? The answer to this is complex and multifactorial – and certainly the possibility of encouraging an increase in potentially risky recreational use will be very much at the forefront of any discussion.

All new drugs require rigorous testing before they meet the standards required, with studies often taking years to complete. The research in Australia, Israel and the US is nearing completion and I suspect we will have more convincing evidence on this topic in the next 12 months.

Currently in New Zealand, the Minister of Health does have the power to authorise the medicinal use of cannabis products, with each case decided individually. In June this year, teenager Alex Renton did receive approval from Peter Dunne to be treated with Elixinol (a hemp-based medication), which was I believe the first application to be granted for this drug. This to me is heartening – hopefully the Government really is willing to look at this complex issue, and make decisions for those who need it most.

However, until approval and use are more widely available, many patients and families around New Zealand continue to use illegal natural cannabis to manage their symptoms – not necessarily a safe alternative, as titrating the dose and predicting the side effects can be difficult, but definitely a decision I fully understand.

Cathy Stephenson is a GP and medical forensic examiner.