Researchers looking into the use of horse tranquiliser and 'party drug' ketamine say they have had a 75 per cent success rate in using it to treat long-term depression.

"The results are startling," says Melbourne University neuroscientist Associate Professor Graham Barrett, who has been studying depression for 30 years.

"They're not 100 per cent, there are people who don't respond to ketamine, but the results are very, very good."

First used as a battlefield anaesthetic during the Vietnam War, ketamine was approved for use in Australia as an anaesthetic and for pain relief.

But it is also used as an animal tranquiliser and taken as a hallucinogenic 'party drug' known as Special K.

Les Jackson has struggled with depression for years after being seriously injured in a motorcycle accident.

He describes the experience of taking ketamine in a clinical trial as "really wonderful".

"When you think about taking your own life - you can't get much more down than that - to where I am now, it has been so good."

From depressed to well in one day: researchers

Professor Colleen Loo, from the Black Dog Institute, carried out clinical trials of ketamine at the University of New South Wales in 2012 and is seeking funding for further research.

"It's truly amazing both in terms of how powerful the effect is, but also how quickly it works," she said.

"Other treatments we know, medications, psychological therapy, electro-convulsive therapy, take weeks to work.

So the fact that you can go from being depressed to being well in one day is unheard of."

While ketamine is not yet approved for the treatment of depression in Australia, it can be used in clinical trials, and is also being offered off-label in some medical centres.

Each treatment costs $150, with patients requiring five treatments of the drug administered via injection, according to Associate Professor Barrett.

"Ketamine as an anti-depressant is well established in the USA and is now an accepted mode of therapy, officially sanctioned, and Australia is lagging behind," he said.

"The aim is to make this available to people, but at the same time to very carefully document what happens and to publish these results as soon as possible."

Psychiatrists urge caution, patients describe impact

However, Professor Loo says she thinks it is "too early to be releasing ketamine for general clinical treatment".

"When we have a new treatment we need to answer three main questions: does it work, how do you give it, what dose, how many times, [and] thirdly, is it safe?" she said.

"We haven't adequately answered those three questions with ketamine."

But Mr Jackson said the impact on his life had been powerful.

"I've gone back to some of my old interests; playing a bit of music, trying to get back to work, organise a business for myself; it's put a lot of ticks in a lot of boxes for me," he said.

"After you have tried so many different avenues and then you get a successful one, it is really good."

Another patient, Tania McClune, had all but given up on finding a treatment.

"Twenty years of depression, treatment-resistant, every time I try to take anti-depressants, I either start vomiting, or they just don't work, either one or the other," she said.

After a series of ketamine injections, she said she was a different person.

"I am just happier and want to participate in a lot more things, which I never used to do," she said.

"I used to wake up and think I can't be bothered, now I think 'just go do it'. That is a major difference, a good difference."

Challenge is to develop safe ketamine tablets

It is too early to talk about a cure for depression, but Associate Professor Barrett says ketamine offers hope to patients.

"The big challenge in the longer term, and this may take five or 10 years, is to develop an orally active form so it can be taken as a tablet," he said.

"But even now, [for] people with severe depression, suffering silently, there is hope, there is treatment."

Professor Loo said she hoped more clinical trials would provide additional evidence of the drug's role in treating depression.

"I think all the signals are very promising, but there are some key questions we need to answer before we can encourage people to say OK, this is now a proven clinical treatment," she said.