Obesity used to be a difficult to treat disease, because in most patients it was problematic to achieve the necessary lifestyle changes on a permanent level. The body-mass index itself is not the optimal measure to show the risks of obesity and it is a substantial mistake in obesitology to skip diagnosing comorbidities and to treat the patient solely on the basis of weight.
Being overweight can be accompanied by serious comorbidities. Treatment with anti-obesity drugs does not have any mortality data; such data exists however for bariatric surgery, as well as for a whole range of drugs used to treat various possible comorbidities, such as certain antidiabetics.
There is an interesting phenomenon dubbed the obesity paradox - the situation where we know that in some cases, the prognosis of an obese patient can be better than that of a slim patient. It is however not certain whether in such paradoxical cases would weight reduction help or harm the patient.
An interesting recent paradox is the issue of obese diabetics. Those always benefit from weight reduction, but it is interesting that even though the treatment of obesity used to be more difficult in their case than in non-diabetics, the opposite is now the case, thanks to modern antidiabetics.
It is due to these complicated uncertainties regarding which risks get genuinely affected and when that it is beyond all doubt that obesity should be treated by a qualified physician not by laymen advisors.