https://en.wikipedia.org/wiki/Treatment-resistant_depression...
Treatment-resistance is relatively common in cases of Major Depressive Disorder. Rates of total remission following antidepressant treatment are only 50.4%. In cases of depression treated by a primary-care physician, 32% of patients partially responded to treatment and 45% did not respond at all.
I'm not advocating withholding help from any of them. It's more of a philosophical quandary.
If you believe (as I do) that the universe is indifferent to human suffering, that life has no greater purpose beyond this one life, and that minimizing human suffering is worthwhile; then the idea of forcing someone to live a life of pain bothers me. And at the same time, the idea of a suicide increasing the suffering of those left behind also bothers me.
It's probably impossible to avoid this degenerating into a religious debate, but those are my thoughts.