When we talk about drugs, or see the myriad array of pharmaceutical ads, we usually hear about a whole range of unique side effects.  These are not just side effects, they are real effects with real medical consequences.

This is true not just for the complex, highly marketed drugs, but even from our most basic antibiotics. While we’ve come think of this class of drugs as almost free from consequence,  the truth is they may have bigger and more far reaching consequences than the drugs that may cause individual problems.  For these drugs, the side effects may be to our whole species and to the ancient human microbiome that makes up a large part of who we are as individuals and as a species. We may be seeing these consequences every day, in the increase in childhood asthma, autism, obesity, and certain types of cancers.  

This discovery has been the life's work of Dr. Martin Blaser.  He examines this in Missing Microbes: How the Overuse of Antibiotics Is Fueling Our Modern Plagues

My conversation with Dr. Martin Blaser: