Unlike the other reviewer, I do not work in mental health. But I would recommend this book to anyone. It has a deeply important message - that loneliness is not just a troubling and painful psychological experience, but rather harmful to phyical health. Perhaps more importantly, the experiences of loneliness creates a vicious circle in which the sufferer's social intelligence is impaired, causing them to misread people's attempts to include them, become less trusting, less persevering and more prone to retreat further into isolation and pessimism. Thought-provoking stuff...
The book helped me to look again at periods in my own life where I have felt lonely, and think again about the consequences this feeling led to.
I have only not given it five stars because individual chapters are not very well structured. The book itself has a three part structure, which works. But too often I found myself reading a variation on the overall theme, without being clear on how this fitted into his argument.
But putting aside these issues, this is an excellent, important and timely piece of work.