Nembutal was once commonly used to treat insomnia. It's not available over the counter in the United States anymore, but the FDA-approved human uses include treatment of seizures and as a short-term hypnotic. And veterinarians use it as an anaesthetic and to euthanize sick animals.
Marilyn Monroe and others died from Nembutal overdoses.
The drug is, however, available in Mexican pet stores over the counter. Nitschke has accompanied terminally ill patients on trips to buy it. At closed workshops -- open only to those who pay a fee of about $40, are older than 50 and of sound mind -- Nitschke gets into the details.
"You have to think, what happens if I vomit?" he says. "There's a lot of knowledge involved and I suppose over the years I've acquired a lot of it."
Nitschke was the first doctor in the modern world to legally kill his patients. In 1996, Australia's Northern Territory, his home state, legalized doctor-assisted suicide.
"I built a machine," he says. "They pressed a button on the machine, the machine delivered the drugs and they died in the arms of the persons they loved."
In all, Nitschke helped four people die before the law was overturned. "People said, 'Sunday is the day I want to die," he says. "Come around and make that possible.'"
Nitschke says he never questions what he is doing in light of the judgment of others or the biblical prohibition against killing. "I mean, I knew I was doing the right thing," says Nitschke, who says he's not religious.
Now that the practice is illegal in his home state, Nitschke has hit the worldwide lecture circuit -- he's due to conduct workshops in the United States in November -- providing suicide tips and campaigning for the right to die.
Euthanasia, in some form, is legal only in Thailand, Switzerland, Luxembourg, Belgium and Holland, as well as Washington State and Oregon. And only the terminally ill qualify in most of those places. Not so to join Exit International.
"It doesn't have to be serious disease," Nitschke says. "It doesn't have to be pain. I think we should respect the right of rational adults to make this choice."
His support of death for rational adults like Lisette Nigot, a healthy Australian woman who decided when she turned 80 that enough was enough and she would kill herself, has alienated more moderate elements in the pro-euthanasia movement.
"I was saying things like, 'Why don't you go on a world cruise? Why don't you write a book?'" Nitschke says. "She ended up saying, 'Why don't you mind your own business. What I want from you, Philip, is technical information.' So I gave her the information and she died."
Nitschke admits his information could fall into the wrong hands.
"Now, we do not knowingly give information to people who are psychiatrically impaired," says Nitschke, who attempts screen people at the meetings. "Now, some people might come along to my workshops and they might not declare this and they might get access to information, they might ultimately harm themselves. And people argue that because that could happen, no one should get the information."
But Nitschke argues that those who want it, those who need it and those who are of sound mind have the right to be given detailed instructions on how to kill themselves, quickly, peacefully, legally.