There are significantly more data available than just efficacy studies, therefore complete reliance on RCTs is not necessary. Fortunately, the data on weight gain obtained from open-label and retrospective studies are potentially as reliable and useful as data from RCTs. For example, if we compare data on olanzapine-associated weight gain derived from 6-week double-blind, open-label, and retrospective studies,17,24,25 we see very similar results (4.3 kg, 4.6 kg, and 4.4 kg, respectively).
Several recent comprehensive reviews have concluded that AAPs, compared with typical antipsychotic drugs, are associated with a greater risk for antipsychotic-induced weight gain, and among the AAPs, olanzapine appears to cause the most significant weight gain, while ziprasidone seems to cause the least.