How Safe are Natural Supplements?

Jennifer Brooks, PhD, Sasha Milbeck, Jack Mitchell, Elizabeth Nagelin-Anderson, MA , and Diana Zuckerman, PhD, National Center for Health Research

In their quest for health and beauty, half of all American adults take natural supplements to solve all sorts of problems, such as bodies they think are too big and breasts or muscles that they think are too small. [1] Billions of dollars are spent every year. But do these products really work, and how much do Americans know about their safety?

The U.S. Food and Drug Administration (FDA) requires that supplement companies label ingredients in their products. Companies making supplements need not even inform the FDA before producing or selling their products.  However, eight chemicals are banned. Otherwise, companies are basically free to sell any product that isn’t proven dangerous. In other words, companies making drugs to prevent, diagnose, treat, or cure disease must first prove the drugs safe and effective, but the FDA must show evidence that a supplement is unsafe before it can limit its marketing or sales. And, unlike drugs, the FDA does not regulate dietary supplements for purity or quality. [2] Moreover, unlike drug makers, the manufacturers of supplements are not required to report to the FDA health problems that might be related to their products. A supplement’s “guarantee” does not mean a guarantee to work or be safe.

When they advertise supplements, manufacturers are required to abide by the Federal Trade Commission’s (FTC) regulations, only making claims that are truthful and substantiated. Claims are not allowed to be “misleading,” but in reality, advertisements often stretch the truth. A 2002 FTC report on 300 weight-loss ads — two-thirds of which were for dietary supplements — found many false or misleading claims, including claims of safety made without any scientific data to back them up. [3] These ads often implied safety by highlighting “natural” ingredients. Unfortunately, “natural” and “safe” are not the same thing; arsenic is natural, for example, as are lead and mercury, but it is not safe to eat them.

A study published in October 2018 in the Journal of the American Medical Association (JAMA) reviewed 776 supplements that the FDA found to contain unapproved and sometimes dangerous pharmaceutical ingredients. [4] Most of these adulterated products were for sexual enhancement, weight loss, or muscle building. Drugs found in sexual enhancement products included Viagra or other key ingredients in prescription medications for erectile dysfunction. These ingredients can cause serious health problems, especially if the individual is unaware that he is consuming them. The adulterated weight loss products were likely to contain a laxative or sibutramine, a drug previously sold under the name Meridia but removed from the U.S. market in 2010 due to cardiovascular risks. Many of the adulterated muscle building products contained anabolic steroids that were not listed on the label. These can cause mental problems in the short term and kidney problems, liver damage, and heart problems in the long term. Other adulterated supplements contained antidepressants or antihistamines, which may cause dangerous side effects and can interact with other medications.

Unfortunately, the FDA’s oversight of the supplement industry continues to lag. In March 2021, a study by researchers at Harvard Medical School found that weight loss and sports enhancement supplements contained 9 chemicals that are not approved by the FDA and are prohibited for use in supplements. [5] One of these, Deterenol, is banned by the FDA  because it can cause cardiovascular problems and even cause cardiac arrest.

Why Are Supplement Policies so Inadequate?

Why are there basically no safeguards to protect Americans from dietary supplements that don’t work, are contaminated, or don’t contain the ingredients listed on the bottle?

In 1994, Congress passed the “Dietary Supplement Health and Education Act”, or DSHEA.  That controversial legislation classified supplements as foods rather than drugs, a decision that permitted untested stimulants in these products without being approved or regulated as drugs.  The bill also prevented the FDA from enforcing traditional regulatory requirements, such as manufacturers having to list on their products’ labels what ingredients were included, and in what amounts.  As a result, many ineffective, or even bogus supplement products were legally marketed, making questionable or phony claims about health effects or curing diseases.

  • For example, FDA points out that some supplements are advertised as a cure for diabetes. “Lower your blood sugar naturally.”  “Replaces your diabetes medication.”  These are false or unproven claims, and don’t believe them.
  • Other supplements claim to enhance sexual performance. Many of those supplements have unknown stimulants in unknown quantities that could interact with other medications and harm your health.
  • Supplements manufacturers also promise quick and easy weight loss. Not so, said a senior FDA who revealed, “We’ve also found weight-loss products marketed as supplements that contain dangerous concoctions of hidden ingredients, including active ingredients contained in approved seizure and blood medications, and antidepressants.” [6]
  • FDA warns against supplements that promise to treat autism, stating “Products or treatments claiming to cure autism are deceptive and misleading, because there is no cure for autism. The same is true of many products claiming to “treat” autism or autism-related symptoms. Some may carry significant health risks.”  [6]

When shopping for dietary supplements “let the buyer beware.” Some companies provided accurate information about their products, but others do not.  For example, supplements currently on the market have been advertised as being opioid abuse treatments, when there is no clinical proof of such claims.  A drug making that claim would have to provide scientific proof of that claim, but supplements can get away with it unless or until the FTC investigates.

Here are just a few examples of how dietary supplements can be advertised and sold to millions of Americans who are ignorant of their potential risks.


Pills containing ephedra or ephedrine (also known as ma huang, epitonin, or sida cordifolia) have been widely touted as effective for weight loss and enhanced performance. While the ephedra industry boasts that millions of Americans have used ephedra, scientific research indicates it can cause serious health risks, including heart palpitations, vomiting, and nausea, while providing only limited evidence of health benefits. [7] As a result, the U.S. Department of Health and Human Services cautioned Americans about using dietary supplements containing ephedra. In 2004, the FDA issued a ruling to prohibit the sale of dietary supplements containing ephedrine, but not other types of ephedra. [8]

Why is ephedra still on the market? You can thank Congress. It’s a Catch 22: the products can’t be banned unless proven unsafe, but U.S. law doesn’t require companies to publish studies alerting the public to safety concerns. Who is supposed to pay for the research to evaluate risks? Is it ethical to conduct such studies if the researchers think the product is dangerous? Meanwhile, companies that make millions selling ephedra products lobbied heavily to keep them on the market. [9]

Breast-Enhancing Pills

These products are marketed as offering a non-surgical solution for women who want to enlarge their breasts. The manufacturers suggest that the pills work because their herbs contain phytoestrogen (estrogenic compounds found in plants) and therefore stimulate the growth of breast tissue. The many different pills contain a variety of herbs, but some of the more common ones are fennel seed, saw palmetto, dong quai, blessed thistle, and wild yam. As with many dietary supplements, the marketing of these pills emphasizes “natural” ingredients, seeming to suggest safety. Some manufacturers state, “There are no known side effects.” Having no known side effects doesn’t necessarily mean safety; it may mean an absence of studies on women to find out whether the product causes problems. In fact, we could find no research on either the effectiveness or the safety of any of these products. Although some claims have been made about the health-enhancing effects of phytoestrogens for women, research is still unclear on the effects on humans and what dosages are optimal (and which are too large). [10] Some doctors express concern that pills containing enough estrogen to stimulate breast growth might also increase the risk of breast cancer, since greater exposure to estrogen is related to increased risk of breast cancer. [11]

Dietary Supplements Providing Alternatives to Hormone Replacement Therapy

With warnings about the risks of hormone replacement therapy, many women have turned to “natural” alternatives to treat menopausal symptoms. These include herbal remedies, such as black cohosh, caste tree berry, dong quai, ginseng, evening primrose oil, motherwort, red clover and licorice. They also include supplements with soy or isoflavones.

Unfortunately, this is another case of scant knowledge about the safety or effectiveness of widely sold supplements. With regard to the herbal mixtures available, the authors of a 2002 review of alternative medicine for menopause symptoms noted that these products “should be avoided until research data are available; currently, no safety or efficacy data on such combinations have been published.” [12]

Another study conducted by the National Center for Complimentary and Alternative Medicine (NCCAM) and the National Institute on Aging studied the role of black cohosh in relieving menopause symptoms. They found that whether used alone or in combination with other herbal supplements, black cohosh, did not relieve hot flashes or night sweats in women postmenopause or approaching menopause. Experts at the United States Pharmacopeia, a non-governmental public standards-setting authority for healthcare products, suggest that women who do take black cohosh to relieve menopause symptoms should stop as soon as possible because there is no known benefit.12 Because there is little evidence of the effects of black cohosh it may be best to not take it at all.

A number of other studies looked at the role of dong quai, ginseng, kava, red clover and soy in relieving menopause symptoms. Researchers found that dong quai did not help reduce hot flashes, and it interacts with the blood thinning medicine warfarin, which in combination with herbal supplements, may cause bleeding in women taking the drug.

Research on ginseng showed that it did not help relieve hot flashes, but it did help improve a woman’s mood and overall sense of well-being. Kava also did not help with hot flashes, but it did reduce any feelings of anxiety among menopausal women. It is also important to note that kava is thought to cause liver problems, so women should be cautious when taking kava. As with the other herbal supplements, red clover did not reduce hot flashes and it did not produce any serious side effects. Researchers do warn that because red clover is a phytoestrogen, it might cause harmful effects in hormone sensitive tissue such as breast and uterus tissue. Women who are already at risk for diseases and conditions affected by estrogen, such as breast or ovarian cancer, are advised not to take red clover supplements. [13]

There has been some debate over the effects of soy on menopause symptoms, because the results of studies have been inconsistent.  A meta-analysis published in 2015 found a small but significant reduction in hot flashes. [14]

Research findings revealing the risks of hormone replacement therapy serve as an important reminder that even products widely believed to be beneficial are sometimes found to be dangerous when subjected to well-designed, objective research. The research indicating serious health risks from hormone therapy also has generated new interest and more research on natural supplements that contain hormones or phytoestrogens. Phytoestrogens are naturally occurring estrogen-like compounds that may contribute to diseases such as breast and ovarian cancer.

Moreover, both the Food and Drug Administration (FDA) and the Federal Trade Commission (FTC) have required several companies to stop making claims that products containing phytoestrogens are safe and effective in preventing or treating serious or life-threatening diseases or conditions like cancer, heart disease, and osteoporosis. [10]


It is unwise to trust the claims that manufacturers of dietary supplements make about either the effectiveness or safety of their products. Although there are examples of products’ being tested and passing some sort of efficacy and safety standard, many other products are being sold with seemingly little regard for the consumer’s well-being. The FDA has few options for intervening, and — as we saw with ephedra — we may not know about safety problems until millions of consumers have used these products. In some cases we may be lucky enough to have skeptics call the product into doubt before it is ever used, but this response will probably be rare.

The most recent fads for miracle drugs suffer from the same problems experienced with ephedra and other dietary supplements: many advertisements but little–if any–information about how they work or what they do to our bodies.

FDA’s ability to protect consumers is limited when it comes to dietary supplements.  While the agency has recently cracked down on some claims made for these products, it’s important that consumers do their best to research what is in these products, and in what amounts, before ingesting them.

All articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff

The National Center for Health Research is a nonprofit, nonpartisan research, education and advocacy organization that analyzes and explains the latest medical research and speaks out on policies and programs. We do not accept funding from pharmaceutical companies or medical device manufacturers. Find out how you can support us here.

Additional Resource:

Dietary Supplements. FDA. Current as of April 22, 2019.


  1. Blendon RJ, DesRoches CM, Benson JM, et al. Americans’ views on the use and regulation of dietary supplements. Archives of Internal Medicine. 2001;161: 806-810.
  2. The FDA deems a product “unsafe” when “it presents a significant or unreasonable risk of illness or injury under the conditions of use recommended or suggested in the labeling.” See Report of the Commission on Dietary Supplement Labels (1997).
  3. Federal Trade Commission Weight- loss advertising: An analysis of current trends. 2002.
  4. Tucker J, Fischer T, Upjohn L, et al. Unapproved pharmaceutical ingredients included in dietary supplements associated with US Food and Drug Administration warnings. JAMA Network Open. 2018;1(6):e183337.
  5. Cohen PA, Travis JC, Vanhee C, at al. Nine prohibited stimulants found in sports and weight loss supplements: deterenol, phenpromethamine (Vonedrine), oxilofrine, octodrine, beta-methylphenylethylamine (BMPEA), 1,3-dimethylamylamine (1,3-DMAA), 1,4-dimethylamylamine (1,4-DMAA), 1,3-dimethylbutylamine (1,3-DMBA) and higenamine, Clinical Toxicology. 2021.
  6. Dietary Supplements. FDA. Current as of April 22, 2019.
  7. Shekelle P, Morton S, Maglione M, et al. Ephedra and ephedrine for weight loss and athletic performance enhancement: Clinical efficacy and side effects. Evidence Report/Technology Assessment No. 76 (Prepared by Southern California Evidence-based Practice Center, RAND, under Contract No 290-97-0001, Task Order No. 9). AHRQ Publication No. 03-E022. Rockville, MD: Agency for Healthcare Research and Quality. 2003.
  8. Food and Drug Administration. FDA acts to remove ephedra-containing dietary supplements from market. 2004.
  9. Wolfe SM. Ephedra – Scientific evidence versus money/politics. Science Magazine. 2003; 300(5621):905.
  10. Cassidy A. Potential risks and benefits of phytoestrogen-rich diets. International Journal for Vitamin and Nutrition Research. 2003;73(2):120-126.
  11. See discussions in “Playing to our vanity”, Los Angeles Times, January 14, 2002,, and “A pill touted for breast enhancement”, Newsday, May 13, 2003.
  12. Kronenberg F, Fugh-Berman A. Complementary and alternative medicine for menopausal symptoms: A review of randomized, controlled trials. Annals of Internal Medicine. 2002;137:805-813.
  13. National Institutes of Health. (2008). Menopausal Symptoms and CAM. Retrieved on 19 Apr 2010 from the National Center for Complementary and Alternative Medicine website:
  14. M-n. Chen, C-c. Lin, C-f. Liu. Efficacy of phytoestrogens for menopausal symptoms: a meta-analysis and systematic review. Climacteric. 2015;18(2):260-269.