Atropine / diphenoxylate
"An emergency room doctor prescribed Lomotil for some severe diarrhea that I had been experiencing for days.  Was very dehydrated.  They gave me one orally while I was in the E.R., and my diarrhea stopped so quickly that I was unable to provide them with a stool sample. Lomotil is unreal. It works so incredibly quickly to calm the spasming intestines -- I'm talking a matter of a couple of minutes! "