A cheap SSRI type antidepressant fluvoxamine cut the risk of worsening health (hospital or death) in high risk covid cases treated somewhat early on by about 1/3.
https://www.thelancet.com/journals/langlo/article/PIIS2214-109X(21)00448-4/fulltext
the first large, randomised controlled trial to test the efficacy of fluvoxamine for acute treatment of COVID-19. We found a clinically important absolute risk reduction of 5·0%, and 32% RR reduction, on the primary outcome of hospitalisation defined as either retention in a COVID-19 emergency setting or transfer to tertiary hospital due to COVID-19, consequent on the administration of fluvoxamine for 10 days. This study is only the second study to show an important treatment benefit for a repurposed drug in the early treatment population… Given fluvoxamine’s safety, tolerability, ease of use, low cost, and widespread availability, these findings might influence national and international guidelines on the clinical management of COVID-19.
Mechanism is unclear. Could be anti inflammatory, could be anti-clotting, could be stimulating melatonin which is a supplement thought by some to help with covid.