DRD2 and Parkinson disease: Synergistic effects are observed when used in combination with Levodopa.359,360 Lisuride functions as a dopamine receptor agonist with 5-HT1A receptor agonist and 5-HT2B receptor antagonist for PD treatment.361 Piribedil is a dopamine agonist used with or without Levodopa in a phase III trial to treat idiopathic PD (NCT01519856).362 Bromocriptine is a dopamine D2 receptor agonist for early PD treatment.