There was a time when medicines claiming to do more than one thing tame the bowels, stop the headache, regrow the hair were guaranteed to be snake oil. A person could be confident such medicines did nothing. Eventually, exceptions appeared. A blood-pressure drug called minoxidil, weirdly, also grows hair on people's heads.
Tetracycline antibiotics kill bacteria and relieve rheumatoid arthritis.
Aspirin kills pain, cuts inflammation, reduces the risk of heart attack and probably helps prevent some forms of cancer. Statins originally were approved as treatment for high cholesterol, but it's now clear they help prevent heart attacks and strokes. They probably reduce a person's risk for developing diabetes and Alzheimer's disease. They lower the rate of rejection in people with certain organ transplants. They eventually could have a role in treating some cancers.