The best studied medication in stuttering is olanzapine whose effectiveness has been established in replicated trials. Olanzapine acts as a dopamine antagonist to D2 receptors in the mesolimbic pathway, and works similarly on serotonin 5HT2A receptors in the frontal cortex. At doses between 2.5–5 mg, olanzapine has been shown to be more effective than placebo at reducing stuttering symptoms, and may serve as a first-line pharmacological treatment for stuttering based on the preponderance of its efficacy data. However, other medications are generally better tolerated with less weight gain and less risk of metabolic effects than olanzapine.