Everything a person ingests affects that person's health, so you should have very good reasons for taking supplements, in general, whether in or out of the gym. Do the proper research on the supplements and do not just take the word of those selling these items. Supplements are often concentrated amounts of substances which act similar to drugs within the body because of their high dosages. Just as with medical drugs, one may experience side effects from supplements. Good nutrition will insure better health in the long run, but supplements go beyond nutrition, because they spike the body with substances which may or may not be good in high doses, especially for an extended period of time.
You weren't taking steroids, were you?