Final answer:
Aripiprazole is the best choice of medication for the patient with schizophrenia who experienced weight gain on his current antipsychotic because it has a more favorable weight profile compared to the other options listed.
Step-by-step explanation:
The question is regarding the best choice of medication for a 42-year-old man with schizophrenia who has experienced significant weight gain on his current antipsychotic. Considering the side effect profile, particularly weight gain, and the efficacy of available antipsychotic medications, the best next choice among the options given is:
A. Aripiprazole
Aripiprazole tends to have a more favorable weight profile compared to others like Olanzapine, Risperidone, Quetiapine, and Haloperidol. Olanzapine and Quetiapine are known for their propensity to cause weight gain, Risperidone has a moderate risk, and while Haloperidol has a lesser association with weight gain, it can cause more extrapyramidal side effects. Therefore, Aripiprazole would be the most suitable alternative in this scenario, combining efficacy in treating psychosis with a lower risk of causing weight gain.