People's thought processes are severely impaired in schizophrenia and the more impaired people's functioning is the worse their prognosis. Many studies and literature reviews have suggested that newer 'second-generation' antipsychotics provide greater improvements in people's cognition than older drugs but many of these studies have methodological weaknesses, not least their being funded by the drug industry. A study of 817 people in the U.S. looked into the effectiveness of the newer drugs olanzapine, quetiapine, risperidone and ziprasidone and compared them to the older drug perphenazine. After 2 and 6 months of treatment the results for all the drugs showed a broadly similar improvement in patient's cognitive abilities while after 18 months the older drug perphenazine showed a greater improvement than the newer (more expensive) second-generation drugs.
Keefe, Richard S.E. ... [et al] - Neurocognitive effects of antipsychotic medications in patients with chronic schizophrenia in the CATIE trial Archives of General Psychiatry June 2007, 64(6), 633-647