Solarpunk Farming

Diclaimer: I studied biology but failed biochemistry with a crash.

It is hard. Often, medically used molecules are complex, manufacturing typically has many steps (higher chance that something goes wrong), typically one wants high purity (have to get high purity raw material) some especially annoying substances have right- and left-handed forms and other isomers - the atom count matches, but the arrangement doesn't and in biological systems, arrangement matters.

Some things are doable. If the molecule in question is produced by a microbe that's easy to cultivate, even complex molecules can be produced with DIY methods.

So if there's a nuclear war and you need antibiotics after the dust settles, you can probably set up penicillin production in a few weeks. It all starts with leaving some bread in a dark and damp place to invite fungi, picking the right-looking colony, replicating it, testing it against a dish of bacteria, if it passes the check for having antibiotic effect, then replicating it more and more, harvesting, purifying, stabilizing, storing... (Reality check: you'd be producing really small amounts of an outdated antibiotic to which there's widespread resistance.)

[Disclaimer: unless you know what you're doing, don't do this at home.]

The only time I've done DIY medicine was to help a dachshound with a skin tumour. Since my mother has no other dachshound, there was no control group. The dachshound is old and was not fit enough for a removal operation. Knowing that tumour immunotherapy for dogs was unavailable where I live (and ridiculously expensive where it might be available), I did the crude thing. Visiting every evening, I powdered some siberian chaga (tree fungus) and nutritional yeast (deactivated yeast) and mixed a small quantity of them in wound cleaning alcohol (to ensure all microbes would be dead in the mixture). Cleaned up the tumour with a peroxide solution (it initially bled every day) and put some droplets of the fungus/alcohol mixture on it - to provoke the immune system with quite clear message "look, I'm a hostile fungus and there's two of us, if you don't act now, we'll mess up everything". The reasoning was that the tumour microenvironment had likely locally deactivated immune response and "trolling" it with fungal antigens would activate it (licensed medics do it with far more potent bacterial antigens, to which I had no reliable access). Result: tumour went into remission and dachshound still lives, but it's not a very happy life because he was already ill at the beginning in multiple other ways - ways that I would be hard pressed to influence at all, no matter how hard I tried to synthesize anything - so I don't. Some of the medications cost 100 € per month, but it still makes sense to buy them.

P.S.

If you're prescribed antibiotics (many now come in two components, main ingredient and resistance preventing secondary ingredient), you can always add garlic to your menu to make it extra hard for bacteria to develop resistance. You won't find out if it did you any good, but chances are it might.