The first step in reducing strain on the vocal cords is to learn to use the microphone correctly.
And I am going to steal a line from Jim Carroll's post in the singing lessons thread.
...Most of the older singers of folk songs tended to sing the way they spoke - similar tonal range, same speech patterns...
So try speaking the song a few times before you sing it and then gradually introduce the tune. That way you won't find yourself singing outside of your vocal range.
The only medication that I have found effective is beer. Just don't drink it BEFORE your performance.