Ten years after they became the first countries to legalise euthanasia, the Netherlands and Belgium now provide assisted suicide to 4,000 people a year.
Most have been cancer sufferers but there are now also some with Alzheimer's disease, following a new interpretation of the law.
Since euthanasia became legal in the Netherlands in April 2002, "the statute has remained unchanged, but what has changed is the the way doctors interpret it," said Inge Freriksen, spokeswoman for the Dutch health ministry.
Mercy killing by lethal injection is allowed in the Netherlands for patients who are fully mentally alert but whose suffering has become "unbearable and unending" due to incurable disease.
About a third of all the requests deemed to be "serious" are honoured by doctors, the ministry said.
"The concept of 'unbearable suffering' has become much clearer" over the years, said Eric van Wijlick, policy maker at the Royal Dutch Society of Doctors (KNMG).
Euthanasia was provided to an Alzheimer's patient for the first time last year, something which "would have been unimaginable in 2002," said Walburg de Jong of the pro-mercy killing group Right-to-Die NL.
The overwhelming majority of the 3,136 patients who were euthanised in the Netherlands in 2010 suffered from terminal cancer, about 80 percent choosing to die at home.
Six roving medical teams -- each with a doctor and a nurse -- were recently set up to assist people to die at home when their own local doctors refused to give them lethal injections.
Their intervention has already been requested 100 times since the teams were set up in March, De Jong said.
But this has raised questions in the Dutch medical association.
Euthanasia has become the central point of conversation between a doctor and a patient who is suffering when it should be seen as a "last resort", Wijlick said.
"For those people who expressed the wish to die, death is not always the best solution," he added.
Belgium followed the Dutch example later in 2002 with a law legalising euthanasia after a long debate between Christian and secular parties.
There were 1,133 mercy killings in Belgiun in 2011, representing 1.0 percent of deaths in the country, its Commission for the Evaluation and Control of Euthanasia reported, adding that numbers were growing.
The vast majority -- 81 percent -- of Belgians who choose to die by assisted suicide are Flemish, because of their cultural proximity to the Dutch.
"The (euthanasia) law has been positive, as it has made huge changes in patient-doctor relationships," said Jacqueline Herremans, president of Belgium's Association for the Right to Die with Dignity (ADME).
"Many taboos on the end-of-life have been lifted," she said.
"It allows families to better prepare for it and accept the deaths of their loved ones. They can put in place the rituals, like good-byes and a last meal..," she said.
While most countries forbid mercy killing, the issue is often not clear cut as some allow "passive" euthanasia, when the medical profession is not required to fight to save a patient, or others where patients can refuse medical care.
Explore further: Dutch group launch mobile mercy killing teams