6 Popular Supplements That Could Have Hidden Dangers

6 Popular Supplements That May Have Hidden Dangers

Healthy or risky? Here’s what you need to know about possible harmful effects before you pop that vitamin, mineral, or herbal pill.
6 Popular Supplements That May Have Hidden Dangers
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Updated on September 29, 2025
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Note: The U.S. Food and Drug Administration (FDA) does not approve supplements for safety or effectiveness. Talk to a healthcare professional about whether a supplement is the right fit for your individual health, and about any potential drug interactions or safety concerns.

When it comes to supplements, there’s a lot of hype about their potential benefits. Used properly, some products may improve your health, but others can be ineffective or even harmful.

Here’s what you should know about six supplements that historically have been popular — and in all cases, experts recommend taking them carefully, if at all.

Vitamin D Supplements No Match for the Common Cold

A new study finds vitamin D supplements do not affect the number, duration, or severity of colds.
Vitamin D Supplements No Match for the Common Cold

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1. Vitamin D Supplements May Not Be Necessary — and Can Interact With Medications

Your body needs vitamin D along with calcium to build bones and keep them healthy, and to support immune health, muscles, and brain cells. Some research has also found that vitamin D may prevent diseases like cancer and osteoporosis.

Food sources of vitamin D include some types of fish, such as salmon, mackerel, and sardines; foods with added vitamin D, such as some cereals; juices; dairy products; mushrooms; and egg yolks.

Your body also makes vitamin D when your skin is exposed to direct sunlight.

But more isn’t necessarily better when it comes to vitamin D— and many healthy adults don’t need to spend money on these supplements, says JoAnn Manson, MD, MPH, the chief of the division of preventive medicine at Brigham and Women’s Hospital and a professor of medicine at Harvard Medical School, both in Boston.

Large, randomized clinical trials have shown that vitamin D supplementation isn’t necessarily a cure-all — for instance, in a study of nearly 26,000 U.S. adults ages 50 and older, daily vitamin D supplementation did not result in a lower incidence of invasive cancer or cardiovascular events than a placebo.

Dr. Manson says supplementation may be helpful for some groups: those with a known deficiency; adults ages 75 and older; those receiving osteoporosis treatment; people with malabsorption conditions like Crohn’s disease, celiac, or ulcerative colitis; and breastfed infants. However, it may not be helpful for everyone.

“Randomized trials have shown selective benefits of higher-dose vitamin D supplementation, especially in tamping down inflammation, reducing total autoimmune diseases and also metastatic or fatal cancer, but it has not been found to be a panacea or magic bullet,” says Manson.

One study on mostly healthy people conducted by Manson and her team found that vitamin D supplements can lower C-reactive protein, a key blood marker for inflammation.

The research reveals that countering inflammation may be a possible mechanism to explain why higher-dose vitamin D can reduce autoimmune diseases like rheumatoid arthritis or psoriasis, and reduce the risk of advanced cancers, says Manson.

In fact, one study found that vitamin D supplementation appeared to lower the risk of autoimmune conditions by 22 percent, and those who were compliant with pill-taking had even greater benefits.

But Manson adds that vitamin D supplements have generally not been found to decrease the risk of cognitive decline, depression, type 2 diabetes, respiratory conditions, macular degeneration, atrial fibrillation (a common heart rhythm disorder), or several other health conditions in studies previously conducted by her and her team.

For most healthy people, testing vitamin D levels is not necessary, says Manson.

“For the majority of the population, adequate intake can be achieved through a combination of diet and time outdoors,” she explains.

Ultimately, the biggest risk of taking vitamin D is likely wasting money on a supplement you don’t actually need. But it’s also important to also be aware of potential drug interactions and to speak with your doctor before you add vitamin D to your routine.

Medications that don’t mix well with vitamin D include the weight loss drug orlistat (Xenical, Alli), various statins, such as atorvastatin (Lipitor), thiazide diuretics (such as Hygroton, Lozol, and Microzide), and corticosteroids like prednisone (Deltasone, Rayos, Sterapred).

Plus, very high levels of vitamin D in your blood can cause nausea, vomiting, muscle weakness, pain, loss of appetite, confusion, dehydration, excessive urination and thirst, and kidney stones — so it’s possible to overdo it.

2. St. John’s Wort Can Interact Dangerously With Certain Drugs

St. John’s wort is a plant with yellow flowers that is often used as a supplement. While it’s historically been used to treat a variety of ailments, the most robust evidence suggests it may be helpful in treating mild to moderate depression.

Indeed, it’s been found to be more effective than a placebo and to have similar efficacy to standard antidepressants.

“The research shows consistent positive benefits, but for people who have a more mild set of symptoms, not severe depression,” says Jessica Garay, PhD, RDN, PhD, RDN, an assistant professor at Syracuse University in New York and the owner of Major League Wellness, a health and nutrition consulting company for athletes.

It comes with risks, too, though. St. John’s wort in combination with an antidepressant can cause serious complications, including a life-threatening increase in the brain chemical serotonin.

Some people also turn to St. John’s wort as a home remedy for menopause, with some research suggesting it may help with hot flashes (particularly in women with a history or high risk of breast cancer) — but it’s typically not recommended because of serious drug interactions.

“The biggest issue with St. John’s wort is its medication interactions,” says Denise Millstine, MD, an internist in the department of integrative medicine at Mayo Clinic in Phoenix, Arizona.

St. John’s wort may reduce the effectiveness of other medications, including birth control pills, certain cancer medications, HIV medications, medicine to prevent organ rejection after a transplant, seizure medications, heart medications, blood thinners, and statins.

Before you take St. John’s wort, read up on potential drug interactions and ask your doctor about the risks and benefits of this supplement, as well as how it compares to your other options.

3. Calcium May Be Linked to Hardened Arteries

Calcium is essential for a strong skeleton, but too much of this mineral may be harmful. More than 2,500 mg per day for adults ages 19 to 50, and more than 2,000 mg per day for individuals 51 and over, can lead to problems.

Calcium supplements have also been linked to potential risks such as hardened arteries (atherosclerosis) and a higher risk of heart attacks, though the research is mixed.

“If we're getting way more calcium from a supplement, it's going to increase those blood calcium levels — it's not automatically going to get put into our bones like some people would want,” says Dr. Garay. “If you already have some plaque formed in your arteries, then the excess calcium could theoretically make it worse.”

To be safe, “Get calcium from your diet if you can,” advises Dr. Millstine, noting that research shows that calcium is better absorbed through food than through supplements.

There are various food sources of calcium, including plain low-fat yogurt, tofu, nonfat milk, cheese, and fortified cereal and juices.

4. Fish Oil Supplements May Be a Risk Factor for Certain Heart Problems

Rich in omega-3 fatty acids, fish oil supplements have been touted as a means to reduce the risk of heart disease and other conditions, yet the evidence is unclear and remains controversial.

For example, a recent large cohort study of more than 400,000 participants found that regular use of fish oil supplements might be a risk factor for atrial fibrillation and stroke among the general population, but could be beneficial for progression of cardiovascular disease from atrial fibrillation to major adverse cardiovascular events, and from atrial fibrillation to death. The researchers noted that further studies are needed.

Another review of 37 clinical trials and more than 149,000 participants found that while omega-3s lowered the risk of death from heart disease, especially for those who took EPA alone rather than EPA with DHA, they also came with risks. Those who took omega-3s, particularly EPA alone, were more likely to develop atrial fibrillation.

The American Heart Association doesn’t recommend omega-3 supplements for individuals who don’t have a high risk of cardiovascular disease.

You can get adequate amounts of omega-3s in your diet by eating a variety of the following foods:

  • Fish and other seafood (especially cold-water fatty fish, such as salmon, mackerel, tuna, herring, and sardines)
  • Nuts and seeds (such as flaxseed, chia seeds, and walnuts)
  • Plant oils (such as flaxseed oil, soybean oil, and canola oil)
  • Fortified foods (such as certain brands of eggs, yogurt, juices, milk, soy beverages, and infant formulas)
If you’re thinking about taking fish oil or omega-3 supplements, be sure to talk to your doctor first about possible interactions between these supplements and medications such as warfarin (Coumadin) and other blood thinners.

5. Kava Has Been Linked to Severe Liver Injury

Kava is a plant that has been consumed for many years in the South Pacific Islands, and it’s known for its calming effects.

While research supports using kava for the short-term treatment of mild types of anxiety and insomnia, consumption of the plant has also been linked to severe liver injury, including hepatitis, cirrhosis, and liver failure, and other effects, including skin toxicity.

As a result, the FDA concludes that “indiscriminate” use of kava as a recreational or relaxing beverage is not safe for humans.

Additionally, several drugs may interact with kava, from anticonvulsants to anti-anxiety medications, and any drug metabolized by the liver.

 What’s more, people taking kava need to avoid drinking alcohol due to potential liver harm.

“I don't see any real need for someone to be taking this,” says Garay. “The risk is just too great — and we still just don't even really know fully what the risks are.”

6. Soy Supplements May Not Contain All the Benefits of Soy Foods

Soy and foods that come from soy are excellent sources of protein, and soy foods can also be a good source of dietary fiber, healthy fats, and many nutrients, including potassium and magnesium. Soy foods have also been linked to lower rates of heart disease and may even help lower cholesterol.

Research shows that soy foods such as tofu, tempeh, and soy milk are healthy and safe, and are associated with a decreased risk or no change in risk for cancer, according to the American Cancer Society (ACS).

Some people looking to reap the health benefits of soy may choose to try soy supplements instead of foods. But the ACS doesn’t recommend soy supplements, which can contain much higher amounts of isoflavones, which are phytochemicals naturally found in soy foods.

In some earlier studies in mice and rats, researchers found high doses of soy isoflavones could lead to an increased risk of breast cancer, notes ACS.

Soy supplements may also not contain all the benefits of soy foods.

“This is the problem sometimes with supplements — we get too good at isolating things [like soy isoflavones], that they live by themselves in a supplement and we miss some of that good interaction that comes from other components of the food itself,” says Garay.

When it comes to breast cancer outcomes, there isn’t much evidence to show that soy isoflavone supplements are riskier than soy foods, according to a recent review.

Nevertheless, while more research is needed, the review advises people to obtain isoflavones from food rather than supplements.

“We haven’t figured out yet what it is about the food source of the soy that’s so beneficial, that goes away when we take the supplement,” says Garay.

The Takeaway

  • Some popular supplements, such as vitamin D, may have no or few actual benefits for most healthy people. Others can be downright dangerous, such as kava, which can cause severe liver injury.
  • Certain popular supplements, such as St. John’s wort, can have potentially dangerous drug interactions. Still others, like calcium and fish oil, may be linked to heart problems.
  • Before taking any new supplements, discuss your options with your doctor to weigh the potential risks and benefits for your individual situation, especially if you’re managing an underlying health condition, taking medication, pregnant, or breastfeeding.
EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. Vitamin D. Mayo Clinic. March 21, 2025.
  2. Benefits of Spending Time Outdoors. Centers for Disease Control and Prevention. July 1, 2024.
  3. Manson JE et al. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease. The New England Journal of Medicine. November 10, 2018.
  4. Dong Y et al. Effects of Vitamin D3 and Marine Omega-3 Fatty Acids Supplementation on Biomarkers of Systemic Inflammation: 4-Year Findings from the VITAL Randomized Trial. Nutrients. December 14, 2022.
  5. Hahn J et al. Vitamin D and marine omega 3 fatty acid supplementation and incident autoimmune disease: VITAL randomized controlled trial. BMJ. January 26, 2022.
  6. Barbarawi M et al. Vitamin D Supplementation and Cardiovascular Disease Risks in More Than 83 000 Individuals in 21 Randomized Clinical Trials: A Meta-analysis. JAMA Cardiology. August 1, 2019.
  7. Screening for Vitamin D Deficiency in Adults: US Preventive Services Task Force Recommendation Statement. JAMA. April 13, 2021.
  8. Vitamin D. National Institutes of Health. July 26, 2024.
  9. Vitamin D. National Institutes of Health. November 8, 2022.
  10. St. John’s Wort. National Institutes of Health. May 2025.
  11. Benitez JSC et al. Advantages and Disadvantages of Using St. John's Wort as a Treatment for Depression. Cureus. September 22, 2022.
  12. Benitez JSC et al. Advantages and Disadvantages of Using St. John’s Wort as a Treatment for Depression. Cureus. September 22, 2022.
  13. St. John’s Wort and Depression: In Depth. National Center for Complementary and Integrative Health. December 2017.
  14. Non-hormonal-based treatments for menopausal symptoms. British Menopause Society. September 2024.
  15. Calcium. National Institutes of Health. September 14, 2023.
  16. Are You Taking Too Many Calcium Supplements? Cleveland Clinic. January 6, 2025.
  17. Food Sources of Calcium. Dietary Guidelines for Americans. 2020-2025.
  18. Chen G et al. Regular use of fish oil supplements and course of cardiovascular diseases: prospective cohort study. BMJ. May 21, 2024.
  19. Khan SU et al. Effect of omega-3 fatty acids on cardiovascular outcomes: A systematic review and meta-analysis. eClinicalMedicine (Part of The Lancet Discovery Science). August 2021.
  20. Omega-3 Fatty Acids. National Institutes of Health. 2022.
  21. Soares RB et al. An Updated Review on the Psychoactive, Toxic and Anticancer Properties of Kava. Journal of Clinical Medicine. July 12, 2022.
  22. Memorandum. U.S. Food and Drug Administration. August 11, 2020.
  23. Kava Kava. Mount Sinai.
  24. Soy and Cancer Risk: Our Expert’s Advice. American Cancer Society. March 21, 2025.
  25. A Review of the Clinical and Epidemiologic Evidence Relevant to the Impact of Postdiagnosis Isoflavone Intake on Breast Cancer Outcomes. Current Nutrition Reports. March 21, 2025.
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Member of American College of Lifestyle Medicine
Simran Malhotra, MD, DipABLM, CHWC, is a triple board-certified physician in internal medicine, hospice and palliative care, and lifestyle medicine, as well as a certified health and wellness coach. She is currently practicing part time as an inpatient palliative care physician at Medstar Health after serving as the palliative care medical director at Franklin Square Medical Center in Baltimore for a little over four years.

Dr. Malhotra completed her internal medicine residency at Medstar Franklin Square Medical Center, where she also served as chief resident in 2015. She completed her fellowship in hospice and palliative medicine at Johns Hopkins Hospital in 2016. She was named Top Doc in Palliative Medicine in 2019 and 2020 by Baltimore Magazine.

On a personal note, she is a BRCA1 previvor with a strong family history of breast and female reproductive cancers, and underwent a risk-reducing bilateral mastectomy and total hysterectomy in 2020 at 32 years old. After learning about her own genetic risk of cancer, and grounded in her professional experiences in palliative care, she founded Wellness By LifestyleMD, a platform where she works with and educates women at high risk for cancer with or without genetic mutations on the powerful impact that positive lifestyle changes can have on their quality of life and even longevity.

In addition to being a diplomate of the American College of Lifestyle Medicine, she completed the T. Colin Campbell plant-based nutrition certification in 2019, the CHEF culinary coaching certification in 2020, and the WellCoaches health and wellness coaching certification in 2022. She is a member of the ACLM women’s health member interest group and serves as the co-chair of the breast cancer subcommittee.

Malhotra has been featured on several blogs and podcasts, where she has shared her unique perspectives and experiences from palliative care as well as from being a genetic mutation carrier who is passionate about using lifestyle as medicine.
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