Last year, the supplement industry was worth an estimated $46 billion in the United States alone. It’s a beast of an industry—and can be dangerous if you’re not careful. Supplements do not undergo the same restrictions and regulations as prescription drugs. They are not approved by the FDA and are only “intended to add further nutritional value to (supplement) the diet.” Because of this, a lot of conflicting information around the industry pops up when consumers are trying to better their health.

Inessa Makdulina-Nyzio is a registered nutrition and certified dietician at Dietitian for All. She says there is a right way and a wrong way to supplement. “If you are supplementing correctly, you won’t be harming yourself, but many consumers are not as educated about their body’s processes as they should. According to my clinical experience, if someone isn’t deficient in a vitamin or mineral, supplements may not be needed. This is why clinical evaluations are important.” Someone’s supplemental regiment, or lack thereof, varies from person to person. There are supplements that, in certain circumstances, do more harm than good. Read on to discover 11 that can damage your health—and to ensure your health and the health of others, don’t miss these Sure Signs You’ve Already Had COVID.

While being an essential mineral for the immune system, metabolic function, and wound healing, zinc overuse can cause a copper deficiency, another crucial mineral. Those with low copper levels may develop neurological conditions, sometimes experiencing numbness in the arms and legs. In the context of COVID, there are hundreds of articles that tout the benefits of zinc in treating and preventing coronavirus. “These days, zinc is being overused. Zinc must be balanced with copper, which exists in most foods. Taking too much can create an imbalance, prompting stomach problems and other diseases in the gut,” says Inessa Nyzio, RD.

Often consumed as a drink or in pill form, this supplement comes from a pepper plant native to the South Pacific. Advocates of kava proclaim having an easier time falling asleep and experiencing muscle relaxation, promoting a sensation of positive wellbeing. But taking kava in large doses over an extended period increases toxicity in the liver, nausea, ataxia (loss of muscle control), even photophobia (sensitivity to light). “Kava has been associated with liver injury that can be serious and potentially fatal. However, the exact cause and frequency of the liver damage are unclear,” says Alyssa Pike, RD, a Senior Manager at the International Food Information Council. “Kava can cause digestive upset, headache, dizziness, and other side effects. Long-term use of high doses of kava may cause kava dermopathy, a condition that involves dry, scaly, flaky skin with a yellow discoloration.” Do not take kava if you are on prescription medicine because it may spark negative interactions. Avoid it, especially if you are pregnant or breastfeeding. 

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While there have been studies demonstrating the effectiveness of fish oil in lowering blood pressure and cholesterol, there is not enough evidence to show a link between the supplement and improved heart health. In addition, fish oil may be linked to higher levels of LDL cholesterol: the bad kind. But the most common potential harm in taking this supplement is its interactions with other drugs. According to the Mayo Clinic, because fish oil reduces clotting, taking it along with anticoagulants might increase the risk of bleeding. It can also reduce vitamin E levels, which protect cells from damage caused by free radicals.

The problem is not necessarily vitamin D, but excess. Inessa Nyzio, RD, says, “There is an epidemic of vitamin D deficiency in the United States, and much of the time, people are correcting that deficiency by supplementing.” Along with being essential support for the immune system, it also regulates calcium and phosphate in the body, reinforcing bone strength. But when people take upwards of 60,000 international units of vitamin D every day for an extended period of time, it can cause toxicity, also known as hypervitaminosis D. This creates a buildup of calcium in the blood, leading to kidney problems, vomiting, and frequent urination. Nyzio considers vitamin D “the most overused nutraceutical on the market today.” 

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Normally used to promote hair health, biotin has also been linked to improved skin conditions. That said, there is little evidence to back up these claims. Some reports indicate taking biotin correlates with nausea and skin rashes. If taken above the recommended levels, it can also show falsely high levels of thyroid hormones in blood tests. When getting bloodwork for a yearly physical, inform your doctor about the supplements you take. 

The risk may outweigh the reward when it comes to soy proteins. They have large amounts of estrogen-mimicking compounds associated with certain cancers like breast and prostate. Soy can also affect women’s fertility, negatively impact fetal development, and bring about early puberty. Inessa Nyzio, does not recommend soy at all. “It’s too genetically modified, too controversial when it comes to estrogenic effects, and there’s too much concern in how it’s grown regarding pesticides. If we get food in its pure form, our bodies know how to handle it. There used to be no such thing as soy hotdogs until recently. That’s Frankenfood.”

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Also known as the coneflower, echinacea can be mixed into herbal remedies and is available in most health food stores. Over centuries, people claim this natural solution fights infections such as the common cold. That said, several studies over the years found no definitive evidence linking the ingestion of echinacea to infection treatment. Side effects may include upset stomach, nausea, even difficulty breathing. For those with pre-existing medical conditions like asthma and multiple sclerosis, taking echinacea might make symptoms worse. In addition, people allergic to flowers in the daisy family should avoid this supplement to prevent having an allergic reaction. 

Naturally made in our bodies, vitamin A is crucial for cell growth, vision, immunity, and also possesses antioxidant qualities. Those with pancreatic or eye diseases may benefit from it. But, when taken in high amounts, vitamin A can be harmful. Mild side effects range from headaches to nausea, but more severe reactions could end up in coma, even death. Pregnant women taking high dosages of vitamin A can have children with birth defects.

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A staple in alternative medicine and often described as a catch-all, this herb is possibly effective in lowering blood sugar levels for type 2 diabetes patients. But ginseng is also linked to treating a range of ailments such as insomnia, bleeding disorders, breast cancer, even ADHD, all without conclusive evidence. This product is likely unsafe for pregnant women, and other side effects of ginseng are rapid heartbeat, diarrhea, breast tenderness, vaginal bleeding, and fluctuations in blood pressure. If you develop a severe skin condition, swelling in the face and tongue, or fever, stop taking it right away and call a doctor. The National Institutes of Health studied the effects of long-term ginseng use and found evidence that it may lead to affective disorder, anaphylactic reactions, and reproductive toxicity. 

Named after John the Baptist because it frequently blooms on the biblical figure’s birthday, St. John’s Wort is a flowering plant native to Eurasian regions. Users claim it treats depression, symptoms of menopause, and provides anxiety relief through natural means. While it has shown effectiveness in treating mild to moderate depression, its interactions with other drugs (primarily antidepressants and Xanax) may lower those drugs’ effectiveness. “I tend not to bring that into my dispensary because they interact with SSRIs and practically everything else,” says Inessa Nyzio, RD. People undergoing cancer treatment should also avoid this supplement because taking it can lower the effectiveness of chemotherapy drugs. Refer to the Mayo Clinic’s website to see if this supplement might interact with your prescription. 

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A group of vitamins that the body develops for blood clotting (wound healing) make up vitamin K. “It’s important to be aware of your intake of vitamin K—which is found in high amounts in leafy vegetables like broccoli, collards, kale, spinach and turnip greens—if you are taking an anticoagulant (blood thinner) as part of your medication regimen,” says Alyssa Pike, RD. “Essentially a blood thinner and vitamin K have opposite effects when it comes to our blood, so it’s important to be aware of the dosage of each. People taking a blood thinner need to maintain a consistent intake of vitamin K from food and/or supplements because sudden changes in vitamin K intakes can increase or decrease the anticoagulant effect.” Too much can lead to a range of other health problems: enlarged liver, yellow eyes or skin, decreased mobility, irritability, labored breathing, fainting, even hives. A balanced diet should provide enough vitamin K without having to take a supplement.

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Because supplements are not as regulated as FDA-approved drugs, there is more room for brands to put questionable ingredients into their products. Often, you have no idea how many international units you are actually taking. “It’s the Wild West out there,” says Inessa Nyzio, RD. “So, when shopping, look for brands that are clinician overseen. But the most important thing is to look at the ingredients on the bottles.” She says that brands with good manufacturing practices (GMP) along with clinician oversight are the safest way to go. “You wouldn’t believe some of the added chemicals I find in patients’ supplement regimens.” Some ingredients to avoid are food coloring, titanium dioxide, and hydrogenated oils. Also, be aware that these products have a shelf life and can go bad, losing their effectiveness. Consult with your primary care provider to make sure you are getting the correct supplements based on your needs. And to protect your life and the lives of others, don’t visit any of these 35 Places You’re Most Likely to Catch COVID.