NBI-98854 is primarily used in the treatment of tardive dyskinesia, a movement disorder characterized by involuntary, repetitive body movements. It functions as a vesicular monoamine transporter 2 (VMAT2) inhibitor, helping to regulate dopamine levels in the brain by modulating its storage and release. By selectively inhibiting VMAT2, NBI-98854 reduces the symptoms of abnormal movements without significantly affecting normal motor function. Its pharmacological profile allows for once-daily dosing, offering improved patient compliance compared to other agents in the same class. It is particularly beneficial for patients who are unresponsive or intolerant to other treatments, providing a well-tolerated and effective therapeutic option.