| Supplement | Concern/Population At Risk | Potential Side Effects |
| Caffeine-containing supplements | At high doses, especially in individuals with preexisting heart conditions | High blood pressure and palpitations |
| Yohimbine | Individuals with preexisting heart conditions, those taking antidepressant medication or during pregnancy/breastfeeding | High blood pressure, irregular or rapid heartbeat, heart attack, anxiety and stomach distress Medication interactions |
| Bitter orange | Individuals with preexisting heart conditions, during pregnancy or breastfeeding or while taking certain medications/herbal supplements | High blood pressure, elevated heart rate and decreased milk production Medication interactions |
| Licorice Root | At high doses, especially in people with chronic conditions (e.g., heart, liver and kidney disease), those taking corticosteroids or during pregnancy/breastfeeding | High blood pressure, irregular heartbeat, liver and kidney issues and increased risk of premature delivery Medication interactions |
| Magnesium | At high doses, especially with certain types like magnesium citrate, magnesium hydroxide and magnesium oxide | Bloating, diarrhea or nausea |
| Vitamin C | At high doses | Bloating, diarrhea or nausea |
| Iron | At high doses | Bloating, diarrhea or nausea |
| Zinc | At high doses | Copper deficiency, frequent illness or unusual infections |
| Echinacea | People with autoimmune disorders, allergies to the Daisy family (e.g., daisies, ragweed), those taking immunosuppressants, individuals with chronic conditions (e.g., kidney or liver disease) or in groups with limited safety data (e.g., pregnant/lactating women and children) | Worsened autoimmune conditions Medication interactions |
| Vitamin D | At high doses, especially when paired with calcium | Kidney stones and liver toxicity |
| Calcium | At high doses, especially when paired with vitamin D | Kidney stones |
| Creatine | At high doses in people with chronic kidney disease | Worsened kidney function |
| Vitamin A | At high doses, especially in pregnant or lactating women or individuals with liver disease | Liver damage, birth defects (during pregnancy) |
| Kava | At high doses or prolonged use, especially in individuals taking sedatives (e.g., benzodiazepines or alcohol) or medications/herbal supplements | Liver damage, digestive upset, headache and dizziness |
| Green tea extract | At high doses | Liver damage |
| Vitamin B6 | At high doses | Numbness and tingling in the extremities |
| Vitamin B3 | At high doses | Flushing, dizziness and mood irritability |
| St. John’s Wort | Numerous drug interactions, individuals with liver or kidney disease and in populations with limited safety data (i.e., pregnant/lactating women and children) | Worsened kidney or liver function Numerous medication interactions (e.g., birth control) |
| Ginkgo biloba | Individuals taking anticoagulant medications or with bleeding disorders and populations with limited safety data (i.e., pregnant/lactating women and children) | Increased bleeding risk Medication interactions (e.g., anticoagulants) |
| Fish Oil | Individuals taking anticoagulant or anti-hypertensive medications, seafood allergies or with certain chronic conditions (e.g., type 2 diabetes or liver disease) | Allergic reaction, increased bleeding risk Medication interactions (e.g., anticoagulants) |
These are some of the known concerns and potential side effects with common supplements. This list is not comprehensive, and individual responses can vary. Always talk to a healthcare professional before taking any supplement.
1. Heart Problems
Many people turn to supplements hoping to boost energy, improve athletic performance or support weight loss, but what’s often overlooked are the potential effects on the heart. “Stimulant-like supplements such as high-dose caffeine, yohimbine, bitter orange or licorice root can trigger palpitations, elevated heart rate and spikes in blood pressure. For people with underlying heart disease, even ‘natural’ energizers can raise the risk of arrhythmia or stroke,” warns Pinkey Patel, Pharm.D, NASM-CPT.
Patel warns that if a supplement makes your heart pound, causes a change in blood pressure or triggers other unusual side effects, you should discontinue use and consult a medical professional.
2. Digestive Issues
Dealing with ongoing digestive discomfort? Certain high-dose vitamin and mineral supplements may be to blame. “Bloating, diarrhea, or nausea are common when taking high doses of supplements like magnesium, vitamin C or iron. While mild discomfort may seem harmless, persistent digestive issues can affect nutrient absorption and hydration,” says Fay Kazzi, Ph.D, M.S., RD, a registered dietitian.
For example, certain types of magnesium in supplements—like magnesium citrate, hydroxide and oxide—can have a laxative effect, which may lead to dehydration if ignored.
3. Altered Immune Function
When it comes to taking supplements to support your immune system, more isn’t always better. “Very high doses of zinc, for instance, can suppress immune response and cause copper deficiency. Similarly, echinacea or other immune ‘boosters’ may overstimulate the immune system, worsening autoimmune conditions,” says Patel.
She cautions that if you suddenly feel “run down” with frequent illness or unusual infections after starting a supplement, it may be working against you.
4. Kidney Dysfunction
“The kidneys are responsible for filtering excess nutrients. So they can be put under strain with chronic overuse of certain supplements,” says Kazzi. For example, she explains that excess vitamin D or calcium can contribute to kidney stones. Additionally, high doses of creatine may worsen kidney function in people with pre-existing kidney disease.
As a result, she emphasizes that symptoms like unexplained lower back pain, swelling or changes in urination should be taken very seriously.
5. Liver Damage
The liver plays a crucial role in detoxification and processing nutrients—including supplements. However, when supplements are consumed in excess, this additional burden can lead to harm. “Herbal blends like kava, green tea extract (in concentrated pill form) or high-dose vitamin A have been linked to liver injury,” says Patel.
She adds that if the liver becomes too overwhelmed, this can result in signs of liver damage, such as yellowing of the skin, dark or brownish urine, nausea and unexplained fatigue. If you experience any of these symptoms or other unexplained changes in your health, discontinue use and seek medical attention.
6. Neurological Changes
Despite being marketed to stimulate the mind or boost attention, some supplements can have unexpected side effects on the nervous system. For example, “excess vitamin B6 (pyridoxine) can cause nerve damage leading to numbness or tingling in the extremities. High doses of vitamin B3 (niacin) may trigger flushing, dizziness and mood irritability,” explains Patel.
She notes that the brain is highly sensitive to changes in chemical balance. Therefore, supplements that cause symptoms like mental fog, irritability or neuropathy deserve immediate attention.
7. Medication Interactions
“One of the most overlooked risks of supplements is how they interact with medications. St. John’s Wort, a popular herb for mood, can reduce the effectiveness of birth control, antidepressants and even chemotherapy drugs,” Kazzi explains.
She also shares that supplements like ginkgo biloba and fish oil can thin the blood and increase bleeding risk when combined with anticoagulants (“blood thinners”). For these reasons, you should always openly discuss any supplements you’re currently taking or considering with your healthcare provider to avoid drug-nutrient interactions.
Who’s Most at Risk?
For certain groups of people, the risk of serious supplement side effects is even higher. Both experts note that people with increased risk include:
- Those Who Are Pregnant or Lactating. “Even common herbs like ginseng or excessive vitamin A can be unsafe during pregnancy. The placenta and infant metabolism are highly sensitive,” says Patel.
- Older Adults. Patel notes that age alters how the body metabolizes drugs and supplements, which can increase the risk of liver and kidney problems, as well as drug-nutrient interactions.
- People With Chronic Conditions. People with chronic conditions—such as kidney disease, liver disease or autoimmune disorders—should be especially cautious with supplements, as their bodies may process nutrients differently and be more vulnerable to side effects, cautions Kazzi.
- People Taking Multiple Medications. “Polypharmacy [taking multiple medications] plus supplements is a common recipe for adverse interactions,” says Patel. Be sure to mention any supplements you’re taking or are considering when visiting your healthcare provider.
- Children. With more supplements available in “gummy” form, Patel warns this raises concern over children accidentally thinking they’re candy. She explains that smaller bodies are more vulnerable to overdose, which is why it is crucial to store supplements safely out of reach of children.
- Athletes Taking Unregulated Supplements. Kazzi shares that athletes and fitness enthusiasts who experiment with high-dose or unregulated performance supplements are at risk of hidden contaminants and organ strain. To stay safe, she advises double-checking to make sure the supplement is independently tested.
How to Supplement Safely
First and foremost, Kazzi explains that supplementation should never replace a balanced diet but rather fill in gaps that food alone can’t cover. “I recommend starting with lab work to identify deficiencies before adding any new supplement—this helps you avoid unnecessary or excessive use,” she adds.
Both dietitians also advise following evidence-based dosages rather than marketing claims, and being cautious of anything labeled as “mega-dose.” To ensure safety and purity, look for independently tested supplements. “Reputable seals like USP, NSF or ConsumerLab reduce (but don’t eliminate) risks of contamination or inaccurate labeling,” Patel explains.
Most importantly, Kazzi shares that you should always keep your healthcare provider in the loop about what supplements you’re taking—especially if you’re taking prescription medications, are pregnant or lactating or have certain chronic conditions such as heart, liver or kidney disease.
Our Expert Take
Supplements are becoming increasingly popular with more people including them in their daily routines. While many can support health, some carry risks that shouldn’t be ignored—such as heart problems, digestive or neurological issues, altered immune function, liver toxicity, kidney dysfunction and medication interactions. Taking appropriate doses, paying attention to your body and consulting a healthcare professional before starting a new supplement are simple steps you can take to protect your health.
