Dr. Peter Breggin writes in today's Huffington Post that psychiatric diagnoses frequently change, often in an effort to justify a particular drug. But it's worse than that. Diagnoses change to justify any kind of treatment, or none at all.
In regular modern medicine, a patient presents himself to a doctor with a complaint about how he feels or something which is happening to his body. The doctor listens to the complaint, does tests, discovers some kind of objective biophysical problem, and after making a diagnosis looks to clinical experience or medical literature for a cure, which the patient is offered.
In psychiatry, someone else brings the patient in (often under duress). The doctor listens to and automatically believes complaints about the patient's behavior. A decision is made regarding what to do to the patient (usually drug him) to disable him from behaving in such a disagreeable fashion. Last of all, a diagnosis is looked up to formally justify the chosen "treatment".
Regular modern medicine: Dx first - then Rx. (Dx --> Rx.) The treatment depends on the diagnosis.
Psychiatry: Rx first - then whatever Dx will justify. (Rx --> Dx.) The diagnosis depends on the treatment.
In state nuthouses, involuntarily committed patients are told in so many words that they either take the meds or they'll never get out. It's illegal to tell them that; but they are all told exactly that nonetheless. If somebody steadfastly refuses meds and cannot be legally forced to take them, sometimes the only solution is to change the diagnosis. But this can be done with surprising alacrity.
Several years ago I had a client named Jim. He had gone from Chester Mental Health Center to Alton Mental Health Center to Choate Mental Health Center, never taking the meds he had been prescribed for the psychosis which all the doctors were apparently certain he "had". His Thiem date (when the system would be constitutionally required to release him) was fast approaching, and as it turned out, nobody wanted to litigate a civil commitment.
One day Jim called me and reported, with amazement, that his psychiatrist had taken him into an office and asked what diagnosis he wanted. I'd previously given Jim a copy of DSM-IV-TR, so I said, well, that's easy, just look in the book and find a diagnosis that wouldn't be treated with psychotropic meds. He went to pages 338-343, and told his psychiatrist that he should be diagnosed with Substance-Induced Psychotic Disorder (code 292.11), in remission.
This was quickly done. The Illinois Department of Human Services put together all the necessary documentation to make it look medical, and soon petitioned the criminal court for Jim's release, which was granted. Now years later, he lives with his elderly mother and gets along just fine.
In this case, the nuthouse needed to release Jim as successfully "treated", and they wanted credit for it. Because of the timing, they had to justify his not taking meds. No problem, they just changed his diagnosis accordingly.
Psychiatry: Rx --> Dx. Simple, but quite the fraud.