Green’s Dictionary of Slang

1. see moonshine n. (3)

2. (drugs) morphine.

1953		‘William Lee’ Junkie (1966) 52: I was getting sick and wondered if I would get home to the M.S. I had stashed in my apartment.
1964		H. Selby Jr. Last Exit to Brooklyn 69: Goldie told her she had a box of syrettes and in a few minutes [...] we will go inside and turn on. [...] A little morphine now would be just perfect. O yes, just perfect. O Lordy ... MS and Vinnie!!
1969		R.R. Lingeman Drugs from A to Z (1970) 185: M.S. morphine sulphate.
2001		ONDCP Street Terms 14: M.S. — Morphine.