Can you treat suicidal thoughts?

We know that there are many cases of suicide where the individual was clearly out of his mind when he did the deed. In other cases the point is not so clear. Where are we to draw the line?

It is not easy for man to do so. But in those cases where the man goes deliberately, in full possession of reason, and takes away his life, there can be no doubt. He robs God. There are others again, who by allowing their passions to rule them have laid themselves open to devils that delight in luring them on to the dreadful deed—these though not altogether guilty are yet blameable for the indulgence of their passions by which they become helpless in the hands of these devils. But a man who takes away his life in insanity is not—cannot be held as guilty. He is free from the charge of suicide. 

—Hafed, Prince of Persia