The ANU Medical School's Dr David Caldicott began his one-day crash course in medicinal cannabis by asking for a show of hands: how many people in the room had had a meaningful education on the medicinal uses of cannabis in medical school?

Zero hands went up.

"Same here," confessed the emergency doctor.

"I was taught nothing real on this subject in medical school."

Dr Caldicott went on to tell his audience the main psychoactive ingredient in cannabis, THC, was "one of the safest compounds out there".

"In terms of the science you have to ask yourself: why are we so uptight about this?"

"Flabbergasted" is how Dr Caldicott describes his reaction to the notion that not enough is known about cannabis to make it available to patients.

"It really does irk me when people say we don't know enough about this. When people say that, I'm hearing: you don't know enough about this," he said.

"This is not an academic 'terra nullius'. There is an abundance of knowledge — maybe not of published evidence, but of lived experience."

In a sign of the sensitivity that surrounds the medicinal use of cannabis, the ABC was granted access to observe the session on the basis that the 91 attendees — about a third of them doctors — would remain anonymous.

Despite that, several shared their views.

A grower who hoped to be planting by the end of the year but was frustrated by the licensing process, whereby he's had to present a list of patient clients before being given the go-ahead.

A young war veteran who has a prescription from his doctor in his pocket and grows his own plants but could still be charged if he was pulled over by the police for using cannabis to manage his post-traumatic stress disorder.

The cancer survivor who was once given hours to live but attributes his survival to cannabis oil and now plans to spend the rest of his days fighting to make it available to others.

So many flooded the room at the Crowne Plaza in Spencer Street in Melbourne that hotel staff had to set up more tables. There were GPs, nurses, hospital specialists and a row of "tribal elders" from Nimbin (as Dr Caldicott described them). All wanting to know more.

"There are definitely benefits associated with medicinal cannabis. If you argue with me on this you're just wrong," said Dr Caldicott in his trademark blunt style, as he charted the ups and downs of humankind's rapport with the cannabis plant through history.

'None of us have a clue' on benefits of cannabis

Hemp was one of the first plants ever cultivated, used extensively for food and clothing as well as medicinally. The ancient Chinese had a specific glyph denoting it and Ayurvedic medicine recognised it as an analgesic that, unlike the opium poppy, did not constipate.

Buds have been found in tombs in the Gobi desert and it came to Australia on the First Fleet.

By 1894, concerns about abuse had surfaced; the British Government commissioned the Indian Hemp Drugs Commission report.

Cannabis cultivation trials are currently underway in Victoria. ( Supplied )

But don't think the medical establishment's opposition to the use of cannabis is based on thorough analysis, Dr Caldicott said.

"It's based on the fact that none of us have a clue," he told the workshop group.

"Research into the beneficial effects of cannabis has been actively discouraged ... squashed on the basis of political pressure, not evidence."

Rather than decriminalisation or legalisation, Dr Caldicott prefers to talk of the "medicalisation" of cannabis.

Patients, he says, are seeking a therapeutic experience currently not offered by modern medicine.

"This represents the opportunity for patients maybe to take a little bit more control of their own health," he said.

He pointed the finger at the opiate industry as the source of some of the strongest opposition.

"The opiate industry is worth billions. If you have a plant you can grow in your backyard for a fraction of that price, it's a threat."

Wading through the complex biochemistry that explains the way cannabinoids work on the human body, Dr Caldicott described the cannabis plant as a wondrous "botanical factory", a rich treasure trove of medicinal compounds.

He explained how the chemicals found in the marijuana plant work on a whole array of receptors in the human body and how that means there's enormous scope to influence a stunning range of processes from the modulation of pain and seizure threshold to appetite, digestion and mood.

There are 10 times as many cannabinoid receptors in the brain as there are opiate receptors — though none in the brain stem, which means it's very hard to overdose a patient on cannabinoids in a way that would stop their breathing.

Whereas traditional medicine tends to favour a clear cause and effect with a specific target, medicinal cannabis, Dr Caldicott says, is a drug that works less like a light switch and more like a thermostat, up and down regulating multiple factors all at once.

More complicated, without doubt. But also with the potential to treat several disorders at once — depression and pain, for instance.

Cannabis could be, Dr Caldicott says, the perfect antidote to treat the multifactorial disorders that modern life has spawned in one of the most stressed generations ever to exist.

Dr Caldicott's hope is that by disseminating as much information as widely and freely as possible, change will happen, ushering in a new form of medicine.

"Welcome to our flying school," he told attendees. "Thank you for being our test pilots."