I read your query and I understand your concern. As you seem to understand both Seroquel and Zyprexa are used just to control his behavioral symptoms and do not cure parkinson or dementia. The trouble with drugs of that class, antipsychotics, is that they could worsen parkinsonism. For that reason Seroquel was a good choice because it doesn t cause parkinsonism. Olanzapine (Zyprexa) isn t as safe on that regard, but still little effect on Parkinson s compared to some other antipsychotics, so since Seroquel is causing so much sedation it is a good compromise. Another option is Clozapine which like Seroquel doesn t affect Parkinson s, but I guess doctors fear another possibly serious side effect of it, supression of white blood cell production. I hope to have been of help.