Chemicals have way more effects on human biology than what it has been tested for and side effects noted.
Usually a drugs effects are monitored as the effects are related to the disease being treated. Sometimes drugs are repurposed after they find out that one of the side effects can have therapeutic benefits in other conditions.
An excellent example is that of demeclocycline. It is a chemical cousin of doxycycline, but rarely used as an antibiotic, but is used to treat the syndrome of inappropriate antidiuretic hormone (siadh) in certain patients.
If you are going to take a medication for a long time please note; long term effects of most medication can effect other systems and are not well known.A good example is that of the fluoroquinolone antibiotics and tendon rupture. Be very cautious.
Get current textbooks on biochemistry, physiology, and pharmacology and human pathology and use them as references while doing your research. Don’t forget that not every side effect has been researched in great detail.Good luck.
Low dose naltrexone is a good example. Hard to get a prescription for it but seems to be a miracle drug for some with autoimmune issues
And of course the infamouse anti malaria drug that my Dr tells me is less risky than methotrexate.