Rob Knight, co-founder of the American Gut Project at the University of Colorado in Boulder, works in the lab where the samples are processed. The American Gut Project hide caption

itoggle caption The American Gut Project

Number of providers by state who wrote at least 3,000 prescriptions for Schedule 2 controlled substances in 2012 in Medicare Part D. ProPublica/NPR hide caption

itoggle caption ProPublica/NPR

Radiation therapy is effective in treating breast cancer but typically requires dozens of visits over five to seven weeks. A newer protocol takes just three weeks. Antonia Reeve/Science Source hide caption

itoggle caption Antonia Reeve/Science Source

Marian Grunwald (from left), Earl Elfstrom and Verna Matheson bounced a balloon back and forth with nursing assistant Rick Pavlisich on Dec. 13, 2013, at an Ecumen nursing home in Chisago City, Minn. Glen Stubbe/Star Tribune, Minneapolis St. Paul hide caption

itoggle caption Glen Stubbe/Star Tribune, Minneapolis St. Paul

NPR's analysis of government data found that harsh penalties are almost never used when nursing home residents get unnecessary drugs of any kind. Owen Franken/Corbis hide caption

itoggle caption Owen Franken/Corbis

Bob Smithson, 79, can now hold his head upright and breathe on his own, thanks to a medication for myasthenia gravis. M. Scott Brauer for NPR hide caption

itoggle caption M. Scott Brauer for NPR