[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/

[March 2026] The purpose of this trial is to see if high dosages of montelukast given twice a day slow down Parkinson's disease progression. 

Participants in the treated group are receiving up to 30 mg of montelukast twice a day in the form of patented VersaFilm buccal tablets developed by Intelgenx Technologies. Participants consist of up to 90 people with early to moderate PD who are also on levodopa. The duration of treatment is 18 months, followed by a 3 month washout. The clinical trial began in February 2024 and the estimated end of the trial is 31 December 2026.

Initially Karolinska signed a contract with Intelgenx to supply VersaFilm for their Parkinson's trial. This was during the time period when Intelgenx was conducting its own Alzheimer's clinical trial. In April 2024, Intelgenx's Alzheimer's trial was completed and preliminary results showed that participants taking 30 mg twice a day had cognitive improvement. Intelgenx's biggest creditor Atai Life Sciences months later forced Intelgenx into bankruptcy and took over Intelgenx and their trial. Atai has made no effort to come up with the final results of the Intelgenx trial. I have to wonder what Atai's motive is and if it will provide the correct dosages to the Karolinska trial. 

I emailed the principal investigator Dr Per Svenningsson in 2025 and again in early 2026, but I did not get any reply so I don't know if he actually read them. I suggested that he switch to using generic montelukast in his trial. I also suggested that Karolinska should have the montelukast medication provided by Atai randomly tested for the correct dosage.

https://parkinsonsnewstoday.com/news/phase-2-trial-montelukast-oral-film-starts-dosing/

https://euclinicaltrials.eu/ctis-public/view/2023-504278-39-00

https://www.clinicaltrialsarena.com/news/intelgenx-alzheimers-disease-trial/

[April 2026] Two clinical studies, one in Taiwan and the other in South Korea, were conducted that indicate that montelukast and other cysteinyl leukotrienne inhibitors can be used for cancer prevention. Three leukotrienne inhibitors are available - montelukast, zafirlukast and pranlukast. Montelukast is by far the most prescribed leukotrienne inhibitor worldwide. Zafirlukast has decreased in popularity and is not available in many countries. Pranlukast is only available in Japan and a few other Asian countries.

The first study was conducted by Kaohsiung Medical University in Taiwan. The study was published in April 2016 and was based on enrollment in the Taiwan National Health Insurance Research Database. Patients were selected from adults with newly diagnosed asthma between 2001 and 2011. Among those patients, each leukotrienne inhibitor user was matched with five randomly selected leukotrienne inhibitor non-users by sex, age, asthma diagnostic year and modified Charlson Comorbidity index score. The development of cancer was considered as the outcome. Totally 4185 leukotrienne inhibitor users and 20925 non-users were identified. The results showed that the leukotrienne inhibitor users had a significantly lower incidence of cancer than non-users.Further analysis showed that leukotrienne inhibitors were an independent protecting factor.

https://www.nature.com/articles/srep23979#change-history

The second study was conducted by Seoul National University in Seoul, South Korea. The study was published in April 2022 and the data came from patients enrolled in the Korean National Health Insurance Service. Patients were selected from adults diagnosed between 2005 and 2011. A total of 188,906 patients were matched (94,453 leukotrienne inhibitor users and 94,453 leukotrienne non-users). 

The results showed that the use of leukotrienne inhibitors was associated with a decreased risk of cancer. The cancer risk showed a tendency to decrease rapidly when leukotrienne inhibitors were used in higher doses or for longer than three years. The greater preventive effects of leukotrienne inhibitors were also observed in patients with specific risks factors related to sex, age, smoking and presence of comorbidities. 

https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2022.858855/full

The use of leukotrienne inhibitors shows great promise in preventing cancers. The approved dosage for montelukast for asthma is very low - only 10 mg once a day. Further montelukast has a short half-life of about 4 hours which means that it loses its effectiveness over a 24 hour period. Zafirlukast and pranlukast also have short half-lives which also makes them less effective over 24 hours. Increasing the dosage and frequency over 24 hours would likely increase its effectiveness in preventing cancers.