For example, in a meta-analysis, addition of the partial dopamine D2 receptor agonist aripiprazole to clozapine therapy improved negative symptoms and reduced several adverse effects, such as weight gain and increased prolactin level, whereas a combination of 2 dopamine D2 antagonists was associated with greater prolactin elevation but less insomnia.12 Such a reduced adverse effect burden could also increase adherence. This evidence concerns the gene DRD2 and insomnia measurement.