Some of the most popular drugs used today were originally designed with other purposes in mind. Chance discoveries found other uses for them. Thalidomide, was prescribed to reduce morning sickness but caused profound birth defaults. It has since found new use as an anti-cancer drug.
Minoxidil (Rogaine) does not have such a tragic past but shares a bit of history with another common drug. Both found unusual novel uses in the marketplace.
[See video below or build a minoxidil molecular model]