[March 2026] In a small clinical study published in April 2025, fifteen PD patients were recruited to Karolinksa Hospital in Sweden for a 12-week open-label trial of montelukast taken 20 mg twice a day. Patients underwent ratings with the Movement Disorder Society Unified Parkinson Disease Rating Scale (MDS-UPDRS), the Montreal Cognitive Assessment (MoCA), Beck's Depression Inventory (BDI), Parkinson's Disease Questionnaire-39 (PDQ-39), [11C]PBR28-PET, and lumbar punctures before and during montelukast treatment.

All patients completed the study. No serious adverse events related to treatment were reported. MDS-UPDRS total scores improved by 6.9 points. Montreal Cognitive Assessment scores also showed significant improvement. Biogen in their lecanemab clinical trail did not use the Montreal Cognitive Assessment tests but rather used a different series of cognitive tests. As a comparison, their testing showed that lecanemab treated patients did not show cognitive improvement but only a small (27 percent) slowing of decline. This suggests that montelukast taken 20 mg twice a day is a far more effective treatment than lecanemab for treating patients experiencing cognitive decline.

https://pmc.ncbi.nlm.nih.gov/articles/PMC12006882/