I was given what I was told was a brandname "OxyContin" (40mg) from a trusted friend when I hurt my back at work yesterday. Last night I took half and felt great. When I woke up I felt terrible and almost vomited.

I looked up the pill my friend had given me and couldn't find it. It's a round, white pill with '40' imprinted in gold/yellow lettering. Thanks in advance.