Morphine - I need me some more feen...

 

 Opiates were some of the most widely used medicines in 

19th-century America. During the Civil War, surgeons administered morphine injections and opium pills to soldiers who had endured gunshot wounds and amputations. Opium was also a major remedy for diarrhea and other diseases that spread through army camps during the war. The medicines worked well — too well, in fact. Countless veterans became addicted to opium and morphine, which they continued to take after leaving the army. 

 

There's a great article with more info here:

https://virginiahistory.org/opiate-addiction-civil-war