I found Agnes's Jacket to be a very uneven work. On one hand, I was very moved by the possibility that self-help groups can be a valuable resource. Hornstein spends time in England where the mentally ill are often considered by to be "experts by experience" able to assist one another and insist that the psychiatric professions truly listen to them about the nature of insanity. They exchange ideas on dealing with symptoms that they cannot get rid of; I would think that this might be limited to the higher functioning insane. Others might not be sufficiently articulate, but perhaps different types of groups could help different people.
Hornstein comments that people who hear voices can often help one another cope. That seems very plausible and promising to me. But surely one's underlying attitude toward the voices makes a difference: the person who genuinely believes that there is a radio transmitter in his/her head might not see how practicing yoga would be to the point. I would think that they would feel more in need of a surgeon to remove the transmitter. Still, if self-help is effective, I support it. At least they could be offered the support of people who understand and sympathize with their problems. Unlike Hornstein, I don't think it necessarily follows that there are not underlying chemical bases for some mental illnesses.
Hornstein also quotes an author know as John Custance who suffered from mental illness and wrote books on the subject. (She is very disappointed to find out that his son does not remember life with father fondly.) Custance argued that if a lunatic tells his doctor that he sees a devil, the doctor should regard the devil as being as actual as the lunatic and investigate what kind of devil he has seen. Certainly talking to the lunatic about an imaginary devil may reveal more about the patient's mind, but if the devil is actual, than the lunatic is wasting his time seeing a psychprofessional--he/she should be seeing an exorcist.
I am also not convinced by Hornstein's rejection of insanity, or some of it, as chemical imbalances. If, as she says, professional opinion shifts every forty years or so, I would assume that neither physical nor life history explanations are adequate. It may be that insanity, like blindness, can have a variety of sources and histories. Not all of her examples support her premise. "Peter, from Jesus", for example, had no history of known traumas underlying his sudden breakdown, and found talk therapy irrelevant. If one has read popular works (and I would presume professional literature) about mental illness, one has also read about people who found talk therapy useless and drugs like Prozac a miracle cure, so perhaps the message is that there aren't simple answers. Mental patients, like all patients, need to be listened to. Agnes's jacket, the central symbol of the book, is ambiguous in this regard. It may be a statement from Agnes's point of view, but it is incomprehensible to the rest of the world, even to those who try earnestly to understand it.
Hornstein rejects the chemical imbalance theory because she does not like the assumption that the imbalance is incurable, although it can be treated. It doesn't matter what she doesn't like, it matters what it true. She does not offer any evidence that her preferred support groups cure the condition, and it is ironic that such groups, especially those in the twelve step tradition, has also been severely criticized for arguing that the problem will be life-long.
She also criticizes the chemical treatments because there are problems with side effects. That is very true, and not inconsequential, but it is also true with diseases that are generally agreed to be physical. I stopped taking the medicine I was given for migraines because I hated the side effects, but other people successfully use the same medicine. It really isn't evidence against the chemical imbalance theory, just against carelessness in the use of medication.
On the balance, self-help and guidance from mental patients sounds like it might be promising, but I am not convinced that insanity may not be, in some cases, chemical, and that drugs cannot be helpful.