Determining suitable doses of medicinal cannabis will be crucial for the plant to advance as a treatment for health conditions, University of Newcastle Professor of Clinical Pharmacology Jennifer Martin says.
Professor Martin said her team's research was making progress in this area.
As director of the Australian Centre for Cannabinoid Clinical and Research Excellence, she leads the CARE NSW Trial for patients with advanced cancer.
Patients in regional areas and greater Sydney have been recruited for the NSW Health-funded trial.
The trial will assess a range of cannabis medicines on symptoms that patients with advanced cancer experience. It aims to pinpoint the best dose and frequency of cannabis medicine to control symptoms.
"Gathering this evidence will guide the future prescribing of cannabis medicines for patients with advanced cancer," Professor Martin said.
In the trial, patients are being prescribed a cannabis medicine from a range of products that meet the Therapeutic Goods Administration's standards.
These products include different formulations of the cannabinoid THC [tetrahydrocannabinol] or a combination of THC and CBD [cannabidiol].
THC is a psychoactive part of the cannabis plant that can, when taken, produce feelings of relaxation and bliss. CBD is also a relaxant, but does not produce the same effects as THC.
Emerging worldwide research is showing that both compounds have medicinal qualities for a range of conditions.
In the NSW trial, participants are prescribed cannabis medicine at no cost.
"Patients are being given what the current evidence suggests may be the best drug for them based on the assessment of their clinician," Professor Martin said.
"The patients then provide valuable information back to their clinicians by filling in quality of life surveys and doing blood tests to understand what the cannabis medicine is doing.
"If they get side effects or the drug doesn't work after they've reached the maximum safe dose, we can reduce the dose, stop or switch them onto another product.
"It's a rapid way of finding out which of the cannabinoids are helpful for different symptoms and what sort of dose."
The Australian research centre has established an international advisory group that shares information between Europe, America, Canada, Israel, Brazil and New Zealand.
This collaboration is helping to advance the understanding of medicinal cannabis.
"We are trying to learn from each other and move the research forward together," said Professor Martin, who has just been inducted as a fellow of the Australian Academy of Health and Medical Sciences.
Stigma and the legal and political status of cannabis across the world has hampered clinical research into use of the plant for medicinal purposes.
Nevertheless, human civilisations have been using cannabis for medicinal purposes for thousands of years.
A Fascinating Plant
Professor Martin's interest in cannabis is focused on providing high quality data to help develop drugs to treat illness.
She said much was happening in the medicinal cannabis market in Australia.
One example is a cannabinoid medicine developed for chronic insomnia and backed by clinical trials.
It is now available for prescription to patients in Australia through the Therapeutic Goods Administration's Special Access Scheme. The TGA has also made an interim decision to reschedule CBD to allow the public to buy it over the counter at pharmacies.
Professor Martin said the cannabis plant had "lots of different parts to it".
"Scientifically, it's a very fascinating plant," she said.
"The different molecules bind to different cell-signalling pathways. Some act on the immune system, some act on pathways that regulate fear and anxiety.
"Some of those are different at different doses."
Some patients don't like the feeling of being sedated, while others don't mind it.
"That sometimes is a dose-related thing. You might have to reduce the dose to reduce sedative effects," Professor Martin said.
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Cannabis can reduce anxiety, but if the dose is too high it can increase anxiety. As well as dose, these factors can also relate to the strain of cannabis being used.
There are two types of cannabis plants known as sativa and indica. Sativa generally makes people feel more alert, while indica has more of a sedative effect. These strains are sometimes combined.
In places where medicinal cannabis is legal such as the US, dispensaries sell different strains for different medical conditions.
Professor Martin said more data was needed to "understand the therapeutic significance of the wide range of products becoming increasingly available".
As for the effects of cannabis, they are regulated by the body's endocannabinoid system.
"This system is in a lot of species and has been there for a long time," Professor Martin said.
"In fact, it was there with invertebrates and insects. It's mainly a system to protect us from fear, hunger, pain and adverse temperatures."
It has also been found to regulate activities in the immune and nervous systems.
Humans, and many other animal species also have naturally created endogenous cannabinoids within their bodies. "That's a fascinating area in itself," she said.
Research in this field has found that people with anxiety conditions have an upregulated stress response. In such cases, the natural cannabinoids and their receptors within the body may be deficient or dysfunctional.
For some people, cannabis relieves symptoms of stress, anxiety and appetite issues.
As for the endocannabinoid system, it exists "very deep in the brain".
"People call it the reptile brain," she said.
The cortex, which enables humans to think, was developed on top of the reptilian part of the brain.
"I guess what happened was, over time, the cortex learned how to switch fear off or manage it. Some people with conditions or certain stressors can't easily switch that system off."
Post-traumatic stress disorder, panic disorder, phobias and generalised anxiety disorder are examples of this.
"In medicine, we usually initially try to get people to try non-pharmacological responses for those things like exercise or working with a psychologist," she said.
Benzodiazepines like Valium and antidepressants like SSRIs have been used to treat such conditions.
Benzodiazepines are now prescribed much less because of their potential for dependence, abuse and side effects.
Using cannabinoids may also lead to side effects.
"It's always important to try and address the underlying issues."