An anti-ñ-synuclein drug, or an ñ-synuclein inhibitor, is a drug which blocks or inhibits ñ-synuclein. ñ-Synuclein is a protein which is thought to be involved in the development and progression of ñ-synucleinopathies including Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. Anti-ñ-synuclein drugs are under development for treatment of Parkinson's disease and other ñ-synuclein-related diseases. Examples include the monoclonal antibodies prasinezumab and cinpanemab, which both failed to show effectiveness in slowing the progression of Parkinson's disease in phase 2 clinical trials. Other anti-ñ-synuclein drugs, like the monoclonal antibodies exidavnemab and amlenetug, the ñ-synuclein vaccines PD01A and PD03A, and the small-molecule ñ-synuclein misfolding and aggregation inhibitors minzasolmin and emrusolmin, are also under development. Memantine is also being studied as a potential disease-modifying treatment for Parkinson's disease by inhibiting cell-to-cell transmission of ñ-synuclein and is in a phase 3 trial for this purpose.