The most respected standard source on the effectiveness of medical treatments is the British Medical Journal‘s Clinical Evidence.  This summarizes 2500 treatments studied:

(Here is a summary of older reviews. Hat tip to Harold Lehmann.)

I’ve said we should cut medicine in half, and have so far proposed two methods:

• Raise the price of medicine, first by reducing subsidizes then by increasing patient cost-sharing or by adding taxes.

• Bring in docs from places where spending is low to impose their style of practice on places where spending is high.

Let me add a third proposal:

• Cut insurance coverage for treatments using BMJ ratings: first cut those likely to harm and unlikely to benefit, then cut those with benefit harm tradeoffs and those of unknown effectiveness.

Since randomized experiments and cross regional regressions usually find zero correlation between health and medical spending, we should presume that treatments of unknown effectiveness are on average ineffective.