All the repurposed drugs that are useful have anti-inflammatory properties. @farid__jalali, an MD on twitter, is trying to get a study for the anti-serotonin drug Cyproheptadine going. He's observed several patients get pulled out of death spirals I guess. He's written a paper with some colleagues explaining the role of serotonin in severe COVID-19, and is trying to get this published.
Dr. Jalali has run into medicine's "gatekeepers". I suspect his actual problem is that repurposed generic drugs that saves lives leave money on the table, and undermines the Emergency Use Authorizations [EUA] the vaccines are sold under.
Cinaserin is another anti-serotonin drug that'd probably also be useful for treating the serotonin storm [2] associated with severe COVID-19: https://twitter.com/TaxiCabJesus/status/1385260243492380680
[0] https://news.ycombinator.com/item?id=22993262