The Hidden Dangers of Dietary Supplements

By Pieter Cohen, MD, Cambridge Health Alliance, Harvard Medical School. On Tuesday, April 27, 2010, Dr. Cohen joined Dr. Oz to discuss the hidden dangers of herbal supplements and provided tips on choosing and using them safely.

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Dietary supplements encompass a wide range of products that includes vitamins and minerals, herbal products, amino acids, tissue extracts and other compounds.  Many dietary supplements - which I'll refer to as supplements - are extremely helpful in preventing illness; for example, folic acid can prevent birth defects, and calcium and vitamin D can prevent fractures. 

However, not all supplements are effective.  There are tens of thousands of supplements sold in the US, and while some are very effective, many are not.  Even worse, some might actually cause more harm than good.  Little is known about the safety of supplements, because Congress requires that the US Food and Drug Administration (FDA) assume that all supplements are harmless until proven otherwise.  Because the government does not ensure supplement safety, it's especially important that consumers are careful when purchasing supplements. 

Here, I'll summarize some of the most important safety concerns with supplements and then provide advice for selecting supplements safely.

Manufacturers of supplements do not need to prove that their supplement is effective before selling it. Since there is no required testing of supplements before they are sold, the consumer should keep in mind that information provided on the bottle, brochures or websites are only manufactures' advertising claims.  These statements are not approved by the FDA and the manufacturer can make a claim on the label without providing the FDA (or consumers) with any evidence that it is accurate.

Manufacturers of supplements do not need to inform consumers about side effects even when the ingredients are known to cause side effects. Any ingredient in supplements that has a positive effect on the body also has the potential to have negative effects.  But even when it is established that an ingredient in a supplement causes side effects, the manufacturer does not need to inform the consumer.  For example, bitter orange - a common herbal ingredient in weight loss supplements - causes high blood pressure and racing heart rate.  But when bitter orange is sold, there is no requirement that consumers are informed about these side effects. 

The same is true with medication interactions. Certain supplements, such as St John's wort, can have serious interactions with prescription medications, but there is no requirement that manufacturers provide this information to the consumer.