You might associate the drug ketamine, or Special K, with anaesthesia or partying — but Australian researchers say they have evidence that it can treat depression.

Key points: Pilot program treated 16 over 60 patients with low dose injections of ketamine

Pilot program treated 16 over 60 patients with low dose injections of ketamine All symptoms of depression disappeared among the patients

All symptoms of depression disappeared among the patients Psychiatrists say more research is needed to know about its safety

University of New South Wales researchers at the Black Dog Institute say a pilot program has produced some "astounding" results in a small group of patients over the age of 60.

Professor Colleen Loo led the pilot program treating 16 patients with low dose injections of ketamine, the findings of which were published in the American Journal of Geriatric Psychiatry.

Among the patients treated were people who had suffered from depression for years, and for whom all other treatments — including medications and counselling — had failed.

"What we noticed was that ketamine worked incredibly quickly and incredibly effectively," she said.

"After a single injection of ketamine they could be completely well in a day."

Professor Loo and her UNSW colleagues at the Black Dog institute are in the process of conducting a much larger, three-year trial into the drug's effectiveness as a treatment for major depression.

But she said the pilot program's results were already incredibly encouraging.

"The whole use of ketamine to treat depression, including in the elderly, is really quite revolutionary," she said.

"This has tremendous implications for treating depression in everyone."

The pilot program was a blind, clinical trial, where patients were carefully monitored for two hours after each injection.

"Some people think, 'oh maybe it was just a drug induced temporary high' — and it wasn't," she said.

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"You had the woozy effects in the first hour or so, but the antidepressant effects kicked in later.

"When we asked people about all the facets of depression it wasn't like we thought they were better because of this one thing — like it made you sleep better, or it made you eat better.

"All the symptoms of depression across the board disappeared.

"So they felt better, they were able to enjoy things, they were interested in life, they were able to eat better, they had lots more energy — the whole lot happened at once."

Though ketamine has a reputation among many people as a party drug, Professor Loo said it had been approved for use as an anaesthetic or sedative for humans for decades.

There are now two critical thresholds to be passed before ketamine can be considered a proven treatment for depression.

"We need to have these kinds of results in larger numbers of people, and that's the study we're currently doing," Professor Loo said.

"The second one is, if it's only one treatment the effects tend to wear off after a few days — you need to give multiple treatments.

"The effectiveness and the safety of giving multiple treatments needs to be examined in further studies, and that's what we're also doing in our current study."

More research needed to understand side effects: expert

Psychiatrists have welcomed the research, as there are significant gaps in their knowledge of the use of ketamine to treat depression.

Dr Kym Jenkins, president of the Royal Australian and New Zealand College of Psychiatrists, said until now they were only aware that short-term use of the drug led to a rapid improvement in mood.

"What we don't know enough about is in longer term use of ketamine, what the dosage should be, what the treatment protocol should be, and how safe it is in the longer term," she said.

While the pilot program focused on older patients, Dr Jenkins said the longer trial underway would provide them with the most useful information.

"It's encouraging, especially as this was looking at people over the age of 60 who had otherwise treatment-resistant depression (TRD)," she said.

"Anything, as psychiatrists, that we can find that will help us treat resistant-treatment depression would be a welcome addition to our range of treatments."

But Dr Jenkins said there were risks to using ketamine, and psychiatrists would not advocate its use until much more was known about its safety.

"Occasionally ketamine can produce hallucinatory effects and hallucinatory behaviour… suspiciousness and paranoia, and just disorganisation of thought," she said.

"We need much more clarity around these side effects.

"This is why there needs to be greater determination of what's the appropriate dosage, and what are the treatment protocols — so that you balance out any potential side effects against what could be considerable benefits."