Robin Hanson’s classic article comes to this conclusion:
Perhaps the most striking puzzle in health policy is the apparent lack of an aggregate empirical relation between medical care and health. Observed variations in medical care typically have an insignificant effect on average population health, even when looking at large data sets, sets larger than those which convinced most researchers of the reality of many other influences on health.
Arnold Kling writes
[Hanson] summaries many studies in which two identical populations are compared, with one population receiving “better” medical care (more spending on procedures) and the other receiving less: the average outcomes do not end up different. Since some medical procedures obviously help, he hypothesized that in the aggregate these must be canceled out by procedures that cause unintended harm. I call the harmful procedures “Hansonian medicine.”
Kling goes on to observe that the same finding applies to interventions in education.