Pills and Their Purpose

A row of bottles on the shelf caused me to analyze myself. The yellow pill I have to pop goes to my heart, so it won't stop! A little white one that I take goes to my hands, so they won't shake! The blue one that I use a lot tells my mind I'm happy, but I'm not! The purple ones go to my brain and tell me that I have no pain! The capsules tell me not to sneeze, or cough, or choke, or even wheeze! The red one, smallest of them all, goes to my blood, so I won't fall! The orange ones are big and bright, and they stop leg cramps in the night! Such an array of brilliant pills, helping to cure all kinds of ills! But what I'd really like to know is what tells each one just where to go?