Given that a recent trend analysis ^{Reference Dierickx, Deliens, Cohen and Chambaere1} revealed an increase in instances of euthanasia of people with psychiatric disorders since the Belgian law on euthanasia came into effect in 2002 (despite unresolved matters of great concern), Dr Clifford's call not to ignore the potential risks of euthanasia legislation and practice is indeed essential. Since legalised euthanasia affects directly involved actors as well as healthcare systems and (inter)national societies, discussion of slippery slope arguments is necessary to stay alert and prevent ethically unacceptable acts from being accepted.

At the same time, it is important to safeguard against these discussions becoming purely philosophical, uncorroborated or even leading to a slippery slope fallacy, as might be the case if they are not based on scientific evidence. Hence, it is striking that 15 years after Belgium introduced its euthanasia law, euthanasia among psychiatric patients is still underexamined. Our own study ^{Reference Verhofstadt, Thienpont and Peters2,Reference Dees, Vernooij-Dassen, Dekkers and van Weel3} has concentrated on the reality of clinical euthanasia practice in Belgium and finding ways of improving its transparency and quality.

In an effort to outline this reality, we would like to react to Dr Clifford's assumption that unbearable suffering as a concept might ‘lead almost effortlessly and uncritically to euthanasia’. As we stated in the introduction to our paper, ^{Reference Verhofstadt, Thienpont and Peters2} unbearable suffering is a necessary but not a sufficient condition for granting euthanasia requests in Belgium (other conditions being the competent patient repeatedly making a voluntary and well-considered request, and suffering being rooted in an incurable medical illness without prospect of improvement ⁴ ). Furthermore, for patients who are not terminally ill, the Belgian euthanasia law stipulates the specific legal requirement of due care that two additional independent physicians, one of whom is specialised in the patient's disorder, must be involved in careful assessment and evaluation of all the legal requirements. Hence, in the context of psychiatric patients requesting euthanasia, consultations with at least one psychiatrist are mandatory.

Our study ^{Reference Verhofstadt, Thienpont and Peters2,Reference Dees, Vernooij-Dassen, Dekkers and van Weel3} focused on just one of the key criteria, unbearable suffering, as it represents the most subjective and indeterminate criterion in granting euthanasia requests in the absence of an overarching solid definition and psychiatric assessment tool. In order to contribute to vigilance regarding euthanasia practice, especially concerning psychiatric patients, who are a particularly vulnerable group, the assessment of key criteria such as unbearable suffering should be undertaken as comprehensively and accurately as possible.

It is precisely this scientific involvement that might inform both the slippery slope discussion and the questioning of euthanasia as an end-of-life option on grounds of these arguments. In light of the grave concerns and potential dangers concerning the clinical practice of euthanasia, we strongly believe in scientific evidence as important in informing the juridical, philosophical, political, societal and ethical arguments in this debate. This provides a sound basis both to legitimately question euthanasia and provide sufficient built-in safeguards to protect against potential abuses.