Most patients who made euthanasia requests had depression and/or personality disorders, the study reveals.
Study co-author Dr. Lieve Thienpont, of University Hospital Brussels in Belgium, and colleagues publish their findings in the journal BMJ Open.
In Belgium, euthanasia - defined as a physician's "act of deliberately ending a patient's life at the latter's request" by giving them life-terminating drugs - has been legal since 2002.
According to Dr. Thienpont and colleagues, Belgium, the Netherlands and Luxembourg are the only countries in Europe where psychological suffering or distress is a valid legal basis for euthanasia.
For their study, the team set out to determine whether patients with certain psychological disorders are at greater likelihood of submitting a euthanasia request.
The researchers analyzed the euthanasia requests made by 100 individuals - 77 women and 23 men - on the grounds of unbearable suffering. All patients were receiving treatment for psychiatric disorders at outpatient clinics in Belgium between 2007 and 2011 and were followed-up until the end of 2012.
Ninety-one of the patients had been referred for counseling, while 73 were classed as medically unfit to work and 59 lived alone, according to the study.
More than one psychiatric illness was identified among 90% of patients, according to the team, with depression being the most frequent diagnosis, affecting 58 patients. Personality disorders were the second most common mental illness and affected 50 patients.
Among patients who required further testing, 13 were tested specifically for autism. Of these, 12 were diagnosed with Asperger's syndrome.
Euthanasia requests were accepted for 48 patients, according to the study results, and 35 of these requests were actioned. The remaining 13 requests were delayed or canceled because patients reported that having the option of euthanasia provided them with enough "peace of mind" to carry on living.
By the end of the follow-up period, 43 patients had died in total. Of these, six had taken their own lives, with one of these patients committing suicide because it took too long to approve the euthanasia request.
Thirty of the patients died in a peaceful and positive environment surrounded by family and friends, which the researchers say would not have been possible if patients had died via unassisted traumatic suicide.
Results may help inform euthanasia guidelines for mentally ill patients
Dr. Thienpont and colleagues say their findings may inform the development of future guidelines in relation to euthanasia requests from patients with psychiatric illness, adding:
"Unfortunately, there are no guidelines for the management of euthanasia requests on grounds of mental suffering in Belgium. Taking into account the ongoing fierce ethical debates, it is essential to develop such guidelines, and translate them into clear and detailed protocols that can be applied in practice."
As such, they call for further studies to be conducted - particularly quantitative and qualitative studies - in order to gain a better understanding of euthanasia requests for unbearable suffering among mentally ill patients.
"Furthermore, these studies could undertake systematic comparisons between groups of psychiatric and non-psychiatric patients, thereby exploring the risk factors for, and origins and degree of, unbearable suffering in both patient groups," they conclude.
Earlier this year, Medical News Today reported on a study published in the Journal of Medical Ethics, which found 1 in 3 doctors in the Netherlands would consider helping a patient die if they were suffering from early dementia or mental illness.