Based on individual physiology, (we are all slightly different), most anything could be bad for one’s health, including shellfish, nuts, certain fruits, etc., among those with allergic reactions. Although a certain supplement may be healthy for most people, such as a daily multivitamin and mineral formula (MVM), dosing it incorrectly may have negative health consequences – i.e. more is not better. Also keep in mind that many useful supplements may be contraindicated when using certain medications. As an example, high doses of vitamin E may be harmless for most people but if you were also taking blood thinning medication, it could harmful. It is our position that some supplements can be useful related to health, fitness and sport but we advise against the use of supplements/herbs for medicinal purposes unless working with a qualified physician. Additionally, if you are using medication you should always seek a doctor’s approval to use any supplements.
In line with the spirit of this question, here is a link to the FDA site containing a current list of Dietary Supplement Alerts and Safety Information.
http://www.fda.gov/Food/DietarySupplements/Alerts/default.htm
If you are looking for health and fitness support through supplements and want full product disclosure (rationale for use, safety, contraindications, etc.) you can click the link below to the dotFIT Supplement Reference Guide (SRG) that is used by all our sport/health professionals and published by our Scientific Advisory Board and R&D team. The first section will give you all you need regarding recommendation and manufacturing processes. dotFIT is a research and development company for Sports, Fitness and Health professionals therefore all products must pass our Evidence Based Advisory and Legal committee rules including 3rd party testing procedures. Individual products can be found in respective sections.
http://www.dotfit.com/sites/63/images/misc/SRG_2nd_Edition_2011_FINAL.pdf