Life partners … Nitschke with his partner, Fiona Stewart. Credit:Randy Larcombe Leaving the houses in which he had presided over a death, he says he felt sadness and a heavy sense of responsibility. Then he would look into the sunlight. "There was this immense feeling of being alive. And then taking a deep breath ... and almost immediately, this sexual urge. It was a way I could demonstrate to myself that I was alive. It wasn't me that was dead." Nitschke's honesty can translate into a lack of tact. "He has burnt every other pro-euthanasia campaigner in the country," says one long-term associate, who still counts Nitschke as a friend. In the past he has been described as unshaven and slovenly - and always prickly, always an activist. The relationship with Stewart - a slim, articulate, spiky-haired, full-time law student - has bought him a measure of domestic peace. Stewart, says Nitschke, is like him: "Feisty, outspoken and quite radical in her politics." Importantly, she has never wanted children. Nor does he - something which fractured several of his previous relationships. Nitschke admits to scattiness. He drives a bright orange car partly, he admits, because he was sick of losing his vehicle in car parks. He is jerky, chaotic and passionate, yet clearly deeply committed to his patients, his voice breaking sometimes when he talks of them. During the interview his mobile phone rings several times. It is his patients, worried about the end of life, trying to get hold of him.

Stone cold tequila … with Nembutal and a margarita in Mexico. Credit:Courtesy of Philip Nietschke Nitschke advocates a "peaceful pill" being freely available to anyone of sound mind over the age of 50. Face to face, he admits that while the age limit is Exit International's official position, his own "deeply held personal view" is that it should be available to every adult of sound mind. If 18-year-olds are sent to kill in Afghanistan, why can we not trust them with decisions over their own life? This, he believes, is a frontline human-rights issue. A right to life must carry with it a right to surrender that life. Nitschke's The Peaceful Pill Handbook, a guide to ending one's life co-written with Stewart, is banned in Australia but can be downloaded on the internet. People can subscribe to and get updates on technological advances in the means of death, and new sources of the euthanasia drug of choice, Nembutal. Sales of the handbook now form Nitschke's biggest source of income: on an average day, $400 flows directly into his bank account. Just say no … anti-Nitschke protestors in Ireland in 2011. Credit:Courtesy of Philip Nietschke Nitschke believes technology is about to collapse the entire system of medico-legal control over the means of death. Already, the internet is allowing people to order Nembutal from China. Once, a trip to Mexico or Peru was necessary to buy the drug. Now, packets of white powder are flooding in, creating a fresh demand for testing to make sure that the Chinese powder is the real deal. During the interview for this profile, Nitschke is jet-lagged from a tour of Europe - where he's been running workshops for 150 people at a time on methods of death - but is still full of nervous energy.

He is dealing with a logistical problem. He has been marketing cylinders of nitrogen under the brand name "Max Dog Brewing". Nitrogen can be used for making beer - but, accompanied with an "Exit Bag" over the head, it also provides a means of suicide that is not detectable in an autopsy. We have a lot of things in the cupboard which, if misused, can bring about death. But we don't say, 'Oh, this insecticide can cause death, let's ban it.' Providing someone cleans up the equipment afterwards, users can avoid having "suicide" written on their death certificates. This, together with the fact that buying and owning the cylinders is entirely legal, makes Max Dog Brewing popular. Nitschke has had more than 500 orders, and is struggling with packing and transport issues. Within the week, he is planning to take his mobile laboratory, housed in a grey van with a subtle Exit International logo, to the eastern state capitals. There he will park discreetly, probably in an Exit member's backyard, and provide the means for those who have bought the Chinese powder to test what they've paid for. Nitschke sets up the equipment for testing and provides the instructions, but is careful to stay on the safer side of a blurry legal situation. He never takes possession of the powder. The testing is provided as a free service to the rather ironically termed "life members" of Exit.

Many of his clients, Nitschke says, will never use the drugs, the exit bags or the gas they buy - but having them near, knowing they have the means for a peaceful death within their grasp, brings them "an enormous sense of well-being". He only wishes he could provide the same relief for his mother, Gwen Nitschke. Gwen is the reason Nitschke is living in Adelaide, rather than his beloved Northern Territory. She has had to move into a nursing home. Every time he visits, she asks if he can help her to die. Gwen Nitschke is not sick. Even if the law were changed to allow doctors to assist the terminally ill to die, it wouldn't help her. She is an example of a growing category of people Nitschke finds himself advising - those who are simply tired of life. The people in the nursing home have already quizzed her about whether she has discussed suicide with him. "Of course I have," she replied. She is being closely watched by the staff, and so is he. If the peaceful pill were freely available to all, what would prevent it from falling into the hands of the depressed? "We have a lot of things in the cupboard which, if misused, can bring about death," he says. "But we don't say, 'Oh, this insecticide can cause death, let's ban it.' We stick a label on it saying 'Don't drink this'. You make sure people understand it's dangerous, and that if you take it you will die." The fact that some people are depressed doesn't mean that others should not have access to the peaceful pill, he argues. "Yes, it might fall into the hands of the mentally unwell, but in my more unguarded moments I might have said something like, 'This is the price you have to pay'. " Nitschke argues from a utilitarian perspective. A freely available peaceful pill would bring well-being to the elderly and unwell. This must be weighed against the risks of misuse.

And what about those who are not of sound mind? Nitschke has "no trouble" with the idea that they should be committed to mental hospitals and given counselling. But if, after all this, a person still wants to die, then they should be allowed to do so. "We might find people at the age of 20 saying, 'I am not in any treatable way affected by a psychiatric malady, and I want to die.' Now I don't think we should be stopping those people. If we can't fix a person, we shouldn't be saying we are going to keep you in some kind of safe house until you see the benefits and joys of existence." Philip Nitschke was born in 1947 in Ardrossan, a small town two hours' drive from Adelaide. He describes the family dynamic growing up as "uncomfortable" due to tensions between his schoolteacher parents, who divorced once Nitschke and his older brother and sister had grown up. Before that, the family moved from one tiny South Australian town to another, his parents often running two-teacher schools between them. Nitschke went to high school in Adelaide, boarding with a family he didn't know, where he was sexually assaulted by the man of the house. As a way of escaping the situation, he took a hunting knife and slit the throat of the family's pet dog, something that, robbed of context, has been used against him ever since. In the 1960s, he was a long-haired, left-leaning university student, demonstrating against the Vietnam War while achieving brilliant results in his science degree. For a final-year honours' project, he created Australia's first hologram - but while he gained a first-class degree, he also had to answer for kicking down a laboratory door to get access to his equipment.

After graduation he enrolled in a PhD at Flinders University, which he completed despite a rocky relationship with his supervisor. When he found out that the university was accepting funding from American high-tech weapons companies he denounced it in the media. This ended any prospect of, or desire for, an academic career. Instead, he went to Wave Hill in the Northern Territory to support a landmark struggle by the Aboriginal Gurindji stockmen, who had gone on strike in 1966 over pay and conditions, a dispute which lasted for nine years and eventually became one of the first struggles for land rights. Nitschke spent two years as the community's administrative manager. It came to an end when his long-term partner left him. "I collapsed in a heap, and couldn't work or sleep," he says. He went to Melbourne, where he worked as a tram conductor and a taxi driver before moving back to the Northern Territory to work as a ranger. Meanwhile, there was a succession of women. One of these relationships resulted in the birth of a son, Philip, in 1977 in Alice Springs. The relationship between the parents was on-again, off-again. "Our temperaments meant we were never suited to each other," says Nitschke. Philip jnr grew up mostly in Tasmania, and now works as an academic at the University of Tasmania. Nitschke is a grandfather - his son has three young boys - and though he had little role in Philip's upbringing, today he counts him as a friend. They are both interested in craft beer. "As to his politics, I just don't know. I'm not entirely sure what Philip thinks of my work. It's not an issue we've discussed in detail." Nitschke's career as a ranger was finished by an accident in which he broke his leg. After that, in midlife, he began studying for his medical degree. There was another driver for this career shift. For most of his adult life he has suffered from mental health problems - in particular extreme hypochondria. It began in his student days, when he was planning to marry. Blinding headaches convinced him he had a brain tumour. After tests turned up nothing, a doctor suggested the cause was psychological. The wedding was cancelled on the power of a doctor's note, and the headaches disappeared. Then Nitschke, at 20, was persuaded to undergo psychiatric assessment as a voluntary inpatient at Royal Adelaide Hospital.

He found himself in a frightening world. He was given questionnaires on issues such as whether or not his soul ever left his body. At first he did his best to fill them out honestly. He was told he was suffering from serious psychiatric problems. Nitschke wanted none of it. He began to answer the questionnaires in a way he thought consistent with the doctors' idea of good mental health, and was declared to have made an astonishing recovery. But the hypochondria never left him. It is, he acknowledges, a condition related to obsessive compulsiveness, anxiety and depression, and it has played a role in all his relationship breakups. "I wouldn't want to be stuck with someone like that, either," he says. "If you asked Fiona what drives her nuts about me, that would be the main thing." As he writes in his book, "Living with someone who regularly thinks they're dying can be intolerable." He entered medicine partly in the hope of "educating myself out of it". It didn't work. "Now I have no trouble at all working out new and innovative diseases." When he is in the grip of the fear, he is convinced he is about to die. It hits, he admits, when there is a "flat spot" in his work. "When I get really enthusiastically active in the cause, it is almost as though the cause can be therapeutic." The other reliable relief comes from exercise, to the point of exhaustion. He resists having his condition "medicalised" or treated with drugs. "That's what I am worried about: medicalising the whole human race," he says, reverting to discussion of the elderly: "Antidepressants just pour into nursing homes." Nitschke is presently facing two investigations by the Australian Health Practitioner Regulation Agency (AHPRA). Either could result in him losing his licence to practise. The first, which has been grinding on since 2011, is the result of a complaint from the Therapeutic Goods Administration after Nitschke tried to import Nembutal for a patient suffering from motor neurone disease. Nitschke was using a provision of the law designed to allow the terminally ill to bring in drugs not yet fully trialled. He planned to prescribe Nembutal as a sleeping pill, with strict instructions not to use too much. Whether his patient overdosed would be up to her "as it is with any drug a doctor prescribes". The Therapeutic Goods Administration stopped the import and complained to AHPRA. Meanwhile, his patient killed herself with Nembutal, bought illegally over the internet.

The second complaint, lodged in 2012, comes from right-to-life activists who claim that Nitschke's marketing of the Max Dog Brewing gas cylinders makes him not a fit and proper person to practise medicine. Nitschke receives regular letters from AHPRA saying that they are still investigating these "complex" matters. Even if he loses his licence, he says it won't make much difference to what he does. He would still run his workshops and, in the makeshift laboratory he has constructed in the spare bedroom of the North Adelaide townhouse, conduct his research into new methods of death. Marshall Perron, the former NT chief minister who was responsible for the legislation that propelled Nitschke into the euthanasia movement, remembers encountering the activist doctor first as a "thorn in the side" of his conservative Country Liberal Party government. But the Rights of the Terminally Ill Act brought them together. Nitschke was the only doctor willing to speak in favour of what Perron was trying to do, and willing to implement the law during its brief life. Every year, says Perron, elderly people hang, drown, electrocute and gas themselves. It is a tragedy: "They should be able to die peacefully in the arms of their family." Nitschke's advocacy for a freely available peaceful pill is "an entirely logical position", says Perron. Nevertheless, Perron cannot support him. The risk of abuse by the depressed and "people who could solve their problems in other ways" is too great, he says. Meanwhile, Dr Rodney Syme, vice-president of Dying With Dignity Victoria, thinks Nitschke's workshops on how to die are inherently dangerous: "He assumes everyone is of sound mind, and he can't possibly know that."

It is common, Syme says, for patients dealing with the shock of a terminal diagnosis to think of euthanasia as a first option, whereas treatment might give them many years of quality life. Syme wants laws that would free doctors to frankly discuss the options with their patients on an individual basis and, in the final resort, help their terminally ill patients escape suffering. But, he says, no parliament will ever pass a law that makes the means of death freely available to all. Nitschke's advocacy for the peaceful pill is counterproductive to the cause. A frequent complaint about Nitschke from other pro-euthanasia campaigners is that every time a bill comes up before an Australian parliament - and there have been more than 35 since the NT act was overturned - he swings in to town at the last minute, when a sensitive and difficult parliamentary debate is about to begin, frightening the horses with talk of DYI methods and Exit Clinics. "It is devastating," says one campaigner. "Years of quiet work getting politicians up to the line are undone with a single Nitschke headline." He has even been blamed for the fact that there has been no progress towards law reform in Australia. He rejects the charge. "I have been made a scapegoat for the lack of progress," Nitschke says. "If people want an excuse not to pass the laws, me running around talking about 'do it yourself' isn't going to change anything." In any case, he believes technological advances will soon make law reform redundant. Soon, he says, lethal drugs will be available on blotting paper, like LSD - able to be imported without detection. As for his own end, Nitschke admits that he keeps a supply of Nembutal for his own use. He doesn't want to die "clouded with drugs, tethered to tubes and monitors". Instead, if and when the time comes, he plans to take his bottle of Nembutal to the Gibson Desert and leave his body to the crows.

People affected by the issues in this story can seek support from Lifeline, 13 11 14, and Suicide Call Back Service, 1300 659 467.