You can also check for negative interactions on several sites on the internet if your doctor doesn't know. I hav about 6 of them bookmarked. One of those is associated with Medscape. Type the names of your drug+the name of the supplement you are considering in the google or yahoo search box.
http://www.medscape.com/druginfo/dru...ker?src=google
http://www.drugs.com/
(Look on your left to select what you want to look at or check.)