I have previously introduced the notion that one cannot simply use common sense when practicing medicine. Common sense and intuition are frequently incorrect, and we need science to understand the truth. Here are two more examples for your consideration.
In JACC, Kaltoft et al report on a study of patients getting a coronary stent for a heart attack. In addition to the stent, they used a miniscule filter, which catches debris knocked loose during the stent placement. This small debris (cholesterol, platelets, clot, etc.) otherwise would go further downstream and continue to damage the heart vessels. Makes sense right? Turns out that if they used this device, it increased the number of people who had a second heart attack after the first one. Why would this be? Well, using the extra filter could have done damage to the blood vessel they were fixing. Or, maybe it prevented the stent from being properly deployed.
As I said though, the idea seems good, and it turns out that removing that clot is a good idea, you just have to use a different mechanism. The TAPAS trial showed that if you used a mechanical suction device to remove the clot and debris, you reduced the chance of death at one year by 50%. (The EXPIRA trial suggests a similar benefit with this method) So why does one work, and another method does not? We do not know for sure, and it goes against common sense, but that is why we do science.
Ezetimibe is a drug which has been on the market for a few years now as a cholesterol lowering drug. It was approved for use based on its ability to lower cholesterol, however it has never been shown to actually prevent heart attacks or extend life. JAMA News has a nice discussion of the drug and mentions that a clinical trial large enough to see if ezetimibe is beneficial is underway and should be completed in 2012.