Where can I get information about the side effects of alternative therapies?

Med Teaching centers. The best information may come from studies done at universities or research centers. Online you may try webmd, medscape, mayo clinic, cleveland clinic, harvard, oxford, medline or governmental adencies like cdc.Gov .The pdr from thompson. But never trust the manufacturers or the distribution centers.
NCCAM. The national center for complementary and alternative medicine (nccam) part of the nih is a reliable source of information. Go to their website nccam.Nih.Gov.