I would say, maybe look at medical studies from the opposite end, epidemiological studies look at factors that reduce mortality/morbidity. Granted, it's less flashy, basically vaccines, alcohol/tobacco reduction, increase in active lifestyle, statins/ace inhibitors, monoclonals/oncology fanciness. although someone who actually is an MPH can probably correct me.

on the neuroscience side, off the top of my head, the most impactful things have been better anticoagulants and preventive care for stroke, monoclonal abs for autoimmune diseases like MS/myasthenia, , certain stereotactic brain surgeries, and such. But considering what ails most people, the overall population effect probably is minuscule compared to say better crash safety in automobiles.