A leading mental health organisation says it is considering filing a formal complaint against euthanasia advocate Philip Nitschke.

Dr Nitschke admits he supported Perth man Nigel Brayley in his decision to commit suicide, despite knowing he was not terminally ill, and was only 45 years old.

Mr Brayley began emailing Dr Nitschke after police launched a murder investigation into his wife's death.

He was later found dead with the suicide drug Nembutal in his system. At no stage did Dr Nitschke suggest Mr Brayley seek help for mental illness.

The euthanasia campaigner says Mr Brayley made a "rational" decision to end his life, although he admits he may not be "well-trained" enough to assess the mental health of those who approach him for help.

The Black Dog Institute believes Dr Nitschke had an obligation to recommend psychiatric help to Mr Brayley.

The institute's Dr Caryl Barnes says it may make a formal complaint to the Australian Health Practitioner Regulation Agency (AHPRA), which supervises the registration of doctors qualified to practice.

Dr Barnes says as a psychiatrist, she is "absolutely horrified and appalled" that Dr Nitschke did not recommend counselling.

"I think this gentleman, from my reading, was suffering from most likely a clinical depression and he had an opportunity to be directed towards help and wasn't done so," Dr Barnes said.

"As a medical practitioner, I think he [Dr Nitschke] had an obligation to direct him towards medical help and to encourage him to seek help and to get him screened for a clinical depression."

Dr Nitschke says the Medical Board of Australia is conducting three inquiries examining his medical registration.

He says those interacting with his organisation, Exit International, are not his patients, and he will not "come along and define them as sick and send them off to a doctor".

"They're people that come along and interact with our organisation in a very clear and rational way and I think their views need to be respected rather than defined as sick," he said.

"Maybe I'm not trained well enough but in my opinion they are not psychiatrically ill ... they've made a clear decision that now's the time they wish to die."

Dr Nitschke says he is being contacted by a growing number of people without terminal medical conditions who want to die.

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He says Mr Brayley made a rational decision to commit suicide and he supported that.

"If a person comes along and says to me that they've made a rational decision to end their life in two weeks, I don't go along and say 'oh have you made a rational decision? Do you think you better think about it? Why don't you go off and have a counsellor come along and talk to you?'

"We don't do that.

"If a 45-year-old comes to a rational decision to end his life, researches it in the way he does meticulously and decides that ... now is the time I wish to end my life, they should be supported and we did support him in that."

Western Australia's Mental Health Commissioner Tim Marney has criticised Dr Nitschke for this view.

"The contemplation of suicide is not a rational contemplation," Mr Marney said.

"I think it's extremely concerning that even just the terminology of rational suicide is being used ... it's an oxymoron."

Mr Marney says many people who survive after trying to take their own life are glad they did not die.

"I've had personal experience of a number of people who have committed suicide and a number of people who have tried to commit suicide and are still here, and I can tell you, they thought it was rational at the time," he said.

"Looking back, they're bloody glad they failed."

Psychiatrist Dr Chris Ryan says many people who want to end their lives are depressed and do not have the capacity to make decisions.

Dr Ryan says it would be "almost impossible to make that sort of assessment over email".

The Greens have a bill before Federal Parliament to make euthanasia legal for the terminally ill only.

But Dr Ryan, who is on the board of Dying with Dignity, says Dr Nitschke may have set back the campaign for voluntary euthanasia.

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