A 29-year-old female with schizophrenia has been maintained on risperidone 4 mg daily with adequate symptom control but is experiencing significant hyperprolactinemia manifesting as galactorrhea and amenorrhea. Her prolactin level is 85 ng/mL. The PMHNP plans to cross-taper to aripiprazole. The patient asks why this new medication would not cause the same side effect. Which of the following best explains why aripiprazole has a different effect on prolactin compared to risperidone?