Attempts by doctors to help people suffering from fatal illness take their own lives failed to give an 'easy' death in one in five cases, researchers say.

The claim comes as figures from Oregon, in the US, showed the number of people taking advantage of the state's assisted suicide law doubled last year.

Research into euthanasia in the Netherlands claimed people awake from comas after taking supposedly fatal drug doses and suffer side effects such as vomiting and gasping.

The study showed that when patients tried to kill themselves using drugs prescribed by a doctor, the medication did not work as expected in 16% of cases.

In a further 7% of cases there were technical problems or unexpected side effects.

Problems surface so often that doctors felt compelled to intervene in 18% of cases, according to a report in the New England Journal of Medicine.

Even when the doctor directly performed euthanasia, complications developed in 3% of the attempts.

Patients either took longer to die than expected or woke from a drug-induced coma that was supposed to be fatal in 6% of cases.

'A shock'

Dr Sherwin Nuland, of Yale University School of Medicine, commenting on the report, said: "This is information that will come as a shock to the many members of the public - including legislators and even some physicians - who have never considered that the procedures involved in physician-assisted suicide and euthanasia might sometimes add to the suffering they are meant to alleviate."

And Dr Johanna Groenewoud of Erasmus University, Rotterdam, who carried out the research, said: "Patients who wish to receive help in dying face a small but nevertheless worrisome possibility that some untoward event will prevent the accomplishment of their wish.

"Once the decision to intervene has been made, the goal should be to ensure that death is as merciful and serene as possible."

He looked at 649 cases - 535 where doctors intended to perform euthanasia themselves and 114 where they intended to provide assistance.

Among the 114 assisted cases, two people awoke from their coma and 14 either did not become comatose or took longer to die than expected.

In addition, seven had difficulty swallowing the drugs, four vomited and three developed extreme gasping.

The latest figures from Oregon show 27 terminally ill people, mainly elderly cancer patients, used the assisted suicide law last year, up from 16 in 1998.

Amy Sullivan of Oregon Health Division said: "Although concern about possible abuses persists, our data indicate that poverty, lack of education or health insurance, and poor care at the end of life were not important factors in patients' requests for assistance with suicide."

Malcolm Hurwitt, Chair of the Voluntary Euthanasia Society in the UK, said: "Oregon shows us that the option of legalised physician-assisted suicide can greatly improve care of the dying. Our campaign focuses on the fact that assisted dying should take place within the context of good palliative care - and that's exactly what is happening in Oregon."

But John Airey at the Pro-life Alliance told BBC News Online that the study in the Netherlands "shows how mistaken the Dutch are".

He added: "Far from trying to help patients kill themselves, doctors should be helping them to cope with the problems they have."