Sharing because I found this very interesting.
The Four Thieves Vinegar Collective has a DIY design for a home lab you can set up to reproduce expensive medication for dirt cheap, producing medication like that used to cure Hepatitis C, along with software they developed that can be used to create chemical compounds out of common household materials.
It is, eg lidocaine patches. It has to be injected to really do much. Not aware of any injectables that are over the counter.