Discussing Dietary Supplements

Disclaimer: Views expressed by the author are her own, and not those of USP.

My sister recently contacted me with a link to a dietary supplement her friend was considering purchasing. She had reached out to me to get advice on whether I considered it a safe product. I am not a medical doctor, but I am a chemist, and because of my work I regularly attend talks related to the safety and efficacy of dietary supplements. I was able to outline some of the issues that her friend should consider before taking a dietary supplement, including speaking to a medical doctor familiar with her health history and current medications.

As chemists, we are often called to fill a role as advisors to friends and family, even in areas far outside our specialty. It might be for something relatively silly, like explaining how a chemical reaction works that they saw on YouTube, or it may be for something more serious, like evaluating whether they will spend hundreds of dollars on the internet on a last-ditch attempt to mitigate a fatal disease. They seek out our ability to research an issue, to read scientific literature, and to use logic to temper emotion and come to reasoned conclusions.

When we are asked questions outside of our body of knowledge, it is difficult to appropriately advise the people we care about, and we often seek to learn more about the world around us in order to have more information to share. I hope that in sharing some of the information regarding dietary supplements, you continue to seek out more information to make the best health decisions possible for you and your loved ones.


What is a dietary supplement? The category is broad, with vitamins (Vitamin C), minerals (calcium carbonate), amino acids (L-lysine), botanicals (peppermint), as well as extracts and concentrates included. Dietary supplements can be beneficial, and doctors may recommend a vitamin and mineral supplement in the form of a multivitamin as a way to guarantee appropriate intake of a wide range of nutrients that may or may not be obtained in the diet of their patient. They may recommend more focused supplements, such as vitamin D, to correct for a deficiency after blood tests. Folic acid is regularly recommended to women who wish to become pregnant, as a way to decrease the incidence of certain types of birth defects.

Dietary supplements may also include botanicals based on traditional folk remedies, such as ginger tea for an upset stomach, or peppermint tea to help you sleep. These relatively mild botanicals are used regularly without the guidance of a physician, and for a healthy individual can be very safe. More care needs to be taken when taking stronger botanicals (kava), extracts or botanical oils that may have many times the dose taken in a tea, or when there may be a complicating factor for the person taking the supplement (health issue, prescription or dietary supplement interactions).

I often hear two concerning assumptions regarding dietary supplements. The first is that dietary supplements are “natural” and “natural” substances cannot possibly be harmful. As scientists, we are fully aware that there are many natural substances that can be harmful, and many manufactured substances that can be beneficial. We are also aware that dosing is important, and that while drinking a cup of peppermint tea may be safe, consuming peppermint essential oil or other concentrated products which are made from large quantities of raw material, may not be. We may be able to dissuade friends and family from making this first assumption. The second concerning assumption is that if the supplement is on the shelf at their local drugstore, that it must have been vetted by the FDA before sale and determined to be safe.

Dietary supplement regulation

The FDA does have some regulatory authority over dietary supplements, but does not approve or test supplements before they go to market.The burden is on the manufacturer to ensure the product is safe, any claims made about the product are not false or misleading, and that the product complies with the Food, Drug and Cosmetic (FD&C) Act. FDA has the authority to remove dietary supplements from the market if the product is determined to not be safe, is mislabeled or adulterated, or the market claims are false or misleading.

In order to remove products that are unsafe or make false claims, the FDA must first be made aware that there is a potential problem. This requires the consumer or a medical professional to provide information to the FDA through the MedWatch Program. Unfortunately, consumers often believe that their “natural” supplement could not possibly be the cause of any adverse effects, and do not report the supplement use to their doctors. When using supplements advertised for weight loss and erectile disfunction, consumers may feel embarrassed discussing their supplement use with medical professionals, which leaves FDA unaware of potential unsafe products on the market, and makes it difficult for doctors to provide appropriate care. Some of the possible concerns when taking dietary supplements are outlined below.

Side effects and interactions

The best-case scenario is to have a dietary supplement that has the correct identity, purity, and potency, and that a consumer has discussed with their doctor and/or pharmacist. These medical professionals can advise consumers on what dietary supplements may be useful, and also warn against possible side effects or interactions.

St. John's Wort, shown here, is a commonly marketed homeopathic drug. Photo credit: Bob Peterson. Used under the Creative Commons (CC BY 2.0)
St. John’s Wort, shown here, is a commonly marketed homeopathic drug.
Photo credit: Bob Peterson. Used under the Creative Commons (CC BY 2.0)

St. John’s Wort is a classic example of a dietary supplement that has known interactions with a number of medications. It is used to treat depression and a number of other disorders. It may lower the effectiveness of oral contraceptives, and is notable for interacting with blood thinners such as warfarin (prescribed) and gingko biloba (another dietary supplement). As a result of these interactions, pharmacists may ask if you are taking St. John’s Wort when you pick up a prescription for a blood thinner, and some supplement bottles carry warnings to discuss possible interactions with your doctor. Other interactions are less life-threatening, but may also be less well-known. Black licorice is an example a supplement ingredient that may be used for its sweetening properties, but natural licorice has a compound, glycyrrhizin, which can cause high blood pressure and abnormal heart rhythms.

Supplements that do not contain the advertised ingredient

Some supplements simply do not contain the advertised ingredient. One recent example is a study on African mango seed dietary supplements. Advertisements for African mango seed as the next great weight loss breakthrough abound on the internet. Scientists from the  USDA Agricultural Research Service (USDA ARS) decided to test these supplements to determine which, if any, contained actual African mango seed. They first identified marker compounds for authentic African mango seeds imported directly from Africa, including ellagic acid and related compounds. They then tested three purported seed extracts (purchased from China), and five dietary supplements (purchased online in the US), and determined that only one sample contained African mango seed, and only in trace amounts. In the best case scenario, consumers simply lose money on a product that does not match the label. In other cases, the supplement may be adulterated with other unlabeled ingredients, including potential allergens and prescription drugs.

Supplements that have been adulterated

These are the supplements that I never want my friends and family to take. They include unlabeled ingredients that could range from allergens (peanuts, soy, etc.), to high levels of caffeine, to prescription drugs and drug analogs. The addition of prescription drugs and drug analogs are of particular concern in three categories of supplements: weight loss, sexual enhancement, and muscle building/sports enhancement. The FDA provides a list of tainted supplements they have identified, tested, and removed from the market. Many of the items advertised as “natural sexual enhancement” were determined to be adulterated with drugs to treat erectile dysfunction (sildenafil/Viagra, tadalafil/Cialis), or similar compounds that either have not been tested for safety, or have been removed from the market for safety concerns. The extent of the problem is shown in a recent analysis of 91 “natural sexual enhancement” products, most purchased at convenience stores and gas stations, and the remainder seized by US Customs and Border Control. Of those products, 81% were adulterated with sildenafil, tadalafil, or an analog.

How to keep yourself safe

First, always talk to your doctor and pharmacist about any supplements you are taking, even if you view them as “natural” and safe. Ask if there are any interactions with medicines you are taking that you should be aware of. Companies that produce adulterated supplements specifically target classes of supplements (weight loss, muscle building, sexual enhancement) that people may not feel comfortable discussing openly with their healthcare provider. As a result, adverse reactions to these supplements may be underreported, and resultant health effects may not be attributed to the appropriate cause, leaving these items on the shelf for additional unwitting consumers. If you believe you have had an adverse effect, or if you doctor is concerned that you have had an adverse effect, please report to FDA’s MedWatch program. This is the mechanism which allows FDA to become aware of possible unsafe supplements on the shelf, and to remove them from the market if necessary.

Second, quality matters. Various third party organizations have programs to test dietary supplements to verify that what is on the label matches what is in the bottle.

Three programs for dietary supplement testing include the USP Verified program (disclosure: the author is a USP employee), NSF International, and ConsumerLab.com. Tested supplements can be identified by a symbol on the supplement bottle or they may be listed on the certifying organization’s website.

Finally, critically evaluate product claims. Do not buy a product that seems “too good to be true”. If you want more information (or if you want to share with your friends and family), the FDA, NIH Office of Dietary Supplements, and USDA offer plenty of information on dietary supplements. Dietary supplements, when taken under the advice of a medical professional, properly labeled, and safely manufactured, can be a great benefit to public health. I encourage everyone to become a well-informed consumer, and to assist their loved ones in making choices that lead to a long, healthy life.

Photo credit: healthguage / CC BY 2.0