How do I know if a dietary supplement contains what the label says it contains?

Pharmacist and herbalist Simon Yeung

Pharmacist and herbalist Simon Yeung

Many people search the web, ask friends and family, or look in reference books when they want to know if an herb, vitamin, or dietary supplement can help them and is safe to use.

But another question you might want to ask is whether the supplement contains what the label says it contains — and at the dosage indicated.

Finding the answer to this question is not always easy. Because the US Food and Drug Administration doesn’t regulate dietary supplements as drugs, it provides no guarantee of efficacy or safety — or that the product contents are true to the labeling.  (Although starting in 2010 the agency enhanced its regulations on foods, establishing a system for regulators to track complaints regarding dietary supplements and pull products off the shelves.)

We asked Memorial Sloan Kettering pharmacist and herbalist Simon Yeung, who oversees the Integrative Medicine Service’s “About Herbs” database, whether there are ways that Americans can increase the likelihood that they are purchasing a product that contains nothing more — and nothing less — than what’s listed on the packaging.

He offered the following tips – along with the strong precaution that consumers should always communicate with their healthcare providers about their use of any herbs, vitamins, or any other dietary supplements. He also notes that Memorial Sloan Kettering’s herbal policy does not approve of supplement use for hospital inpatients.

Look for the USP or ConsumerLab label

Dr. Yeung says that a good way to ensure that a dietary supplement is of high quality and not contaminated or adulterated with other materials is to purchase products with labels indicating they have been tested by either the independent, nonprofit US Pharmacopoeial (USP) Convention Dietary Supplement Verification Program or

“A USP-verified product means it contains the listed ingredients at the strength indicated — and is not contaminated with any other substances, such as heavy metals or microbes,” Dr. Yeung explains. “Unfortunately, only a small percentage of products have been reviewed by USP — although the ones it has analyzed are commonly known brands from major companies.”

Another label he recommends looking for is from, a company that collects several brands of a product and independently tests, reviews, compares, and rates them. Part of the company’s process also involves ascertaining that the product contains the listed ingredients and is not contaminated or adulterated. Dr. Yeung notes that while the site accepts advertising, his experience is that “they are pretty good, and if something does not meet their standards for approval, they will report it.”

In addition to labels on dietary supplement packaging, both USP and have websites with detailed information about their findings — although the latter requires a paid subscription.

Dr. Yeung warns that while the approval from either organization is valuable for assessing quality and purity, it does not necessarily indicate effectiveness of a dietary supplement.

 Purchase dietary supplements made in the United States — and from established outlets

Compared to products imported from countries where regulations are unclear or relatively lax, domestically manufactured ones are likely safer, advises Dr. Yeung

“This is one level of assurance, but still no guarantee,” he adds. “For example, the quality and potency of ginseng grown in Wisconsin differs from that grown in other countries, where such variables as the quality of the soil and how the material is transported and packaged is often hard to determine,” he explains.

Dr. Yeung adds that purchasing dietary supplements from a major health store, pharmacy, or other established source provides some assurance of quality as well. “Not to mention that if you buy from an independent sales or marketing person, you are usually charged more for the same thing.”

Select “standardized” products

“At Memorial Sloan Kettering we understand many cancer patients use dietary supplements,” says Dr. Yeung. “We want to help people ensure that the products they take are safe — though it doesn’t necessarily mean they are effective.”

Purchasing dietary supplements that have been standardized, meaning the amount of a specific chemical (known as a chemical marker) is represented on a product label, provides some assurance that the active compound is present in the specified amount desired.

“Natural products have variation from batch to batch,” explains Dr. Yeung. “Time and season can affect potency. While one company might just grind up ginseng root, for example, another may produce an extract of the active constituents that is much more potent. So when purchasing ginseng, look for products standardized to the weight or percentage of the biologically active compound, in this case ginsenosides.

 “Think of standardization information like knowing about the caffeine content in coffee,” explains Dr. Yeung. “A cup of coffee will differ in potency and the effect it has on you because the caffeine content varies across brands.”

The value of reporting use, as well as any bad reactions

Aside from the universal precaution to speak with healthcare professionals about vitamin, herb, or other dietary supplement use, consumers should also take care to communicate with healthcare professionals about cultural or lifestyle practices.

What an American consumer calls a dietary supplement, for example, a person from another country might consider a food or mainstream medicine. Examples include ginger and ginseng, which in Asia are commonly consumed as foods as opposed to viewed as medicines or dietary supplements.

And if consumers do experience adverse reactions with a dietary supplement, they should report it to the FDA’s MedWatch Program,” says Dr. Yeung. “It is important because if the FDA starts to see a pattern — whether it’s related to mislabeling or other issues — it can take action if necessary.”