Pharmacological Strategies to Counteract Anti... [Schizophr Bull. 2014] - PubMed - NCBI

So this study is a meta analysis of interventions into weight loss while on APs they find metformin to be a good addition resulting in a 6 pound weight loss on average and better insulin response etc too. Still it has it's own side effects profile so you know it may not be great for everyone but something to consider...