Apathy shows in 25%–29% of PD patients, who typically exhibit lack of motivation and interests, and reduced emotional reactivity [126,127]. Apathy is often confused with drug-resistant depression, due to their clinical similarity, to the untrained eye. Indeed, the two conditions require different treatments. Apathy can also be a complication following a subthalamic nucleus deep brain stimulation (STN-DBS, see later) procedure [128]. Rivastigmine (9.5 mg transdermal patch daily) was proven to be effective in reducing apathy in non-demented and non-depressed advanced PD patients [128]. DAs as Piribedil, Ropinirole, and Rotigotine, and the dopamine transporter (DaT) inhibitor methylphenidate have also demonstrated to improve apathy in post-STN-DBS apathy, in PD patients [128]. However, ICD is an NMS of PD which can also be triggered by these drugs, so caution is recommended in their administration. Antidepressant agents are not recommended to treat apathy, which could even worsen [128].