Evidence of brain shrinkage:
Quoted from Dr. Joanna Moncrieff, a Senior Lecturer in psychiatry at University College London and a practising consultant psychiatrist, since she did the research:
In 2011, researchers, led by the former editor of the American Journal of Psychiatry, Nancy Andreasen, [...] found a strong correlation between the level of antipsychotic treatment someone had taken over the course of the follow-up period, and the amount of shrinkage of brain matter as measured by repeated MRI scans. The group concluded that "antipsychotics have a subtle but measurable influence on brain tissue loss"
Ho BC, Andreasen NC, Ziebell S, Pierson R, Magnotta V. Long-term Antipsychotic Treatment and Brain Volumes: A Longitudinal Study of First-Episode Schizophrenia. Arch Gen Psychiatry 2011 Feb;68(2):128-37.
In 2005, another American group, led by Jeffrey Lieberman who headed up the CATIE study, published the largest scanning study up to that point of people with a first episode of psychosis or schizophrenia. The study was funded by Eli Lilly, and consisted of a randomised comparison of Lilly’s drug olanzapine (Zyprexa) and the older drug haloperidol. Patients were scanned at the start of the study, 12 weeks and one year later and patients’ scans were compared with those of a control group of ‘healthy’ volunteers.
At 12 weeks haloperidol-treated subjects showed a statistically significant reduction of the brain’s grey matter (the nerve cell bodies) compared with controls, and at one year both olanzapine- and haloperidol-treated subjects had lost more grey matter than controls.
In both haloperidol and olanzapine treated patients,however, there was a consistent effect that was diffuse and visible in most parts of the brain hemispheres.
Lieberman JA, Tollefson GD, Charles C, Zipursky R, Sharma T, Kahn RS, et al. Antipsychotic drug effects on brain morphology in first-episode psychosis. Arch Gen Psychiatry 2005 Apr;62(4):361-70.
Experiment on monkey (could be helpful):
It seems as if Eli Lilly and its collaborators were so confident about their preferred explanation, that they set up a study to investigate the effects of olanzapine and haloperidol in macaque monkeys. This study proved beyond reasonable doubt that both antipsychotics cause brain shrinkage. After 18 months of treatment monkeys treated with olanzapine or haloperidol, at doses equivalent to those used in humans, had approximately 10% lighter brains than those treated with a placebo preparation.
Dorph-Petersen KA, Pierri JN, Perel JM, Sun Z, Sampson AR, Lewis DA. The influence of chronic exposure to antipsychotic medications on brain size before and after tissue fixation: a comparison of haloperidol and olanzapine in macaque monkeys. Neuropsychopharmacology 2005 Sep;30(9):1649-61.
Dr. Moncrieff presented more evidence too (12 papers) and concluded at the end:
What should antipsychotic users and their families and carers make of this research? Obviously it sounds frightening and worrying, but the first thing to stress is that the reductions in brain volume that are detected in these MRI studies are small, and it is not certain that changes of this sort have any functional implications. We do not yet know whether these changes are reversible or not. Of course the value of antipsychotics has been much debated on this site and elsewhere, and their utility almost certainly depends on the particular circumstances of each individual user, so it is impossible to issue any blanket advice. If people are worried, they need to discuss the pros and cons of continuing to take antipsychotic treatment with their prescriber, bearing in mind the difficulties that are associated with coming off these drugs. People should not stop drug treatment suddenly, especially if they have been taking it for a long time.
People need to know about this research because it indicates that antipsychotics are not the innocuous substances that they have frequently been portrayed as. We still have no conclusive evidence that the disorders labeled as schizophrenia or psychosis are associated with any underlying abnormalities of the brain, but we do have strong evidence that the drugs we use to treat these conditions cause brain changes. This does not mean that taking antipsychotics is not sometimes useful and worthwhile, despite these effects, but it does mean we have to be very cautious indeed about using them.