What supplements should you not take long term?

October 10, 2025 •

4 min read

Dietary supplement adverse events lead to an estimated 23,005 emergency department visits in the U.S. each year [1.10.3]. Understanding what supplements should you not take long term is crucial for avoiding toxicity and serious health risks associated with prolonged use.

Quick Summary

Long-term use of certain supplements poses health risks. Fat-soluble vitamins like A and D can accumulate to toxic levels. Minerals such as iron and calcium, and herbs like St. John's Wort and Kava, can cause severe side effects with prolonged intake.

Key Points

Fat-Soluble Vitamin Toxicity: Vitamins A, D, and E can accumulate in the body and cause toxicity with long-term high-dose use, leading to issues like liver damage and an increased risk of mortality [1.2.2, 1.3.3].
Mineral Overload: Long-term supplementation with minerals like iron and calcium can be harmful, causing organ damage, kidney stones, and interfering with the absorption of other nutrients [1.8.3, 1.7.4].
Herbal Supplement Dangers: Herbs such as Kava and St. John's Wort carry significant long-term risks, including severe liver injury and dangerous interactions with prescription medications [1.5.4, 1.2.5].
Beta-Carotene Risk for Smokers: High-dose beta-carotene supplements are linked to an increased risk of lung cancer in people who smoke or have been exposed to asbestos [1.6.1].
Consult Healthcare Professionals: Due to the potential for adverse effects and toxicity, it is essential to consult with a healthcare provider before taking any supplement long-term [1.3.3, 1.2.2].
Lack of Regulation: Dietary supplements are not regulated as strictly as medications, leading to potential issues with product quality, purity, and stated dosage [1.9.4].
Adverse Events are Common: Studies show that adverse events from dietary supplements lead to thousands of emergency room visits annually in the United States [1.10.3].

The Hidden Dangers of Long-Term Supplement Use

While many people use dietary supplements to support their health, not all are meant for indefinite use. The adage "more is not always better" is especially true for supplements, where long-term, high-dose consumption can lead to toxicity and adverse health effects [1.2.2, 1.3.2]. Unlike pharmaceuticals, dietary supplements are not as strictly regulated, which can lead to inconsistencies in product quality and dosage [1.9.4]. An estimated 18% of military service members who use supplements report experiencing at least one adverse effect [1.10.4]. Understanding which supplements carry risks with prolonged use is key to safeguarding your health.

Fat-Soluble Vitamins: A Risk of Accumulation

Unlike water-soluble vitamins that are flushed out of the body when in excess, fat-soluble vitamins (A, D, E, and K) are stored in your body's fat tissues and liver [1.3.3]. This storage capacity means they can accumulate to toxic levels over time, a condition known as hypervitaminosis [1.3.1].

Vitamin A: Chronic toxicity can occur with regular ingestion of more than 10,000 IU daily [1.2.2]. Symptoms include headaches, blurred vision, liver damage, bone pain, and reduced bone strength [1.2.2, 1.2.5]. High doses have also been linked to birth defects [1.2.2].
Vitamin D: While essential for bone health, excessive long-term intake (4,000–10,000 IU/day) can lead to hypercalcemia (high blood calcium) [1.2.2]. This can cause nausea, muscle weakness, kidney problems, and even death in severe cases [1.3.2, 1.2.2].
Vitamin E: High doses (400 IU or more per day) taken for over a year have been linked to an increased risk of all-cause mortality [1.2.2]. It also has an antiplatelet effect, which may increase the risk of hemorrhagic stroke [1.2.2].
Beta-Carotene: For smokers or individuals with a history of asbestos exposure, high-dose beta-carotene supplements (20-30 mg/day) have been associated with an increased risk of lung cancer [1.6.1, 1.6.2].

Minerals: When Essential Becomes Harmful

Certain minerals, while vital for bodily functions, can be harmful when taken in high doses over long periods.

Iron: Essential for preventing anemia, excess iron can be toxic [1.8.3]. High doses can cause gastrointestinal issues like constipation and nausea, and in the long term, may lead to organ damage, particularly to the liver and heart [1.8.1, 1.8.2]. Individuals with hemochromatosis, a genetic disorder causing excess iron absorption, are especially at risk [1.8.3].
Calcium: While crucial for bone health, long-term high-dose supplementation can lead to kidney stones, constipation, and may interfere with the absorption of other minerals like iron and zinc [1.7.4, 1.2.2]. Some research also suggests a potential, though debated, link between high calcium supplement intake and an increased risk of heart disease [1.7.5].
Zinc: Long-term use of high-dose zinc supplements (above 40 mg/day) can cause copper deficiency, nausea, and headaches [1.2.2]. A major study linked 80 mg/day over several years to an increased risk of hospitalizations for genitourinary issues [1.2.2].
Selenium: Chronic high intake can lead to selenosis, with symptoms like hair and nail loss, skin lesions, fatigue, and a metallic taste in the mouth [1.2.2].

Herbal Supplements: Natural Doesn't Always Mean Safe

Herbal supplements can have potent biological effects and interact with medications. Several are not recommended for long-term consumption due to significant risks.

St. John's Wort (Hypericum perforatum): Often used for depression, it can interact with a wide range of medications, including antidepressants, birth control pills, and blood thinners, reducing their effectiveness [1.2.5, 1.4.2]. Long-term use carries risks of side effects like dizziness, dry mouth, and an increased sensitivity to sunlight [1.9.1]. It can also contribute to serotonin syndrome, a potentially life-threatening condition, when combined with other serotonergic drugs [1.4.4].
Kava (Piper methysticum): Used for its calming effects, kava is strongly linked to a risk of severe liver damage, including hepatitis, cirrhosis, and liver failure, sometimes requiring a liver transplant [1.5.1, 1.5.4]. The FDA has issued a consumer advisory regarding this risk [1.5.2]. Scientific evidence does not support the long-term use of kava products [1.5.3].

Supplement Risk Comparison


Supplement	Primary Long-Term Risk(s)	At-Risk Populations	Recommended Action
Vitamin A	Liver damage, bone weakening, birth defects [1.2.2, 1.3.2]	Pregnant women, general population taking high doses	Avoid high doses (>10,000 IU/day) without medical supervision [1.2.2]
Beta-Carotene	Increased lung cancer risk [1.6.1, 1.6.3]	Smokers, former smokers, those exposed to asbestos	Avoid high-dose supplements; obtain from diet instead [1.6.3]
Iron	Organ damage (liver, heart), gastrointestinal issues [1.8.2, 1.8.3]	Individuals with hemochromatosis, men, postmenopausal women	Only supplement if diagnosed with deficiency; avoid high doses [1.8.1]
Kava	Severe liver damage (hepatitis, cirrhosis, failure) [1.5.4]	Individuals with liver problems, those who consume alcohol	Avoid long-term use; consult a healthcare provider [1.5.3, 1.5.4]
St. John's Wort	Dangerous drug interactions, serotonin syndrome [1.2.5, 1.4.4]	People taking any prescription medications (especially antidepressants, birth control)	Consult a healthcare provider before use due to extensive interactions [1.2.5]

Conclusion: Prioritize Safety and Professional Guidance

The potential for harm from long-term supplement use is real and significant. Fat-soluble vitamins and certain minerals can build up to toxic levels, while some herbal remedies pose risks of severe organ damage and dangerous drug interactions. It is crucial to remember that supplements are not a substitute for a healthy diet and should not be taken indefinitely without a clear medical reason and professional oversight. Always consult with a healthcare provider before starting any new supplement, discuss your full health history and all medications you are taking, and be wary of products that make claims that seem too good to be true. Reporting any adverse events to a healthcare professional is also a critical step in ensuring supplement safety [1.2.2].

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional before starting or stopping any supplement.

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Frequently Asked Questions

Fat-soluble vitamins, particularly Vitamin A and Vitamin D, pose the greatest risk for long-term use because they are stored in the body's fat and can accumulate to toxic levels, a condition called hypervitaminosis [1.3.3, 1.2.4]. Chronic high doses can lead to serious health issues like liver damage, bone pain, and high blood calcium [1.3.1, 1.2.2].

For most healthy people, a standard multivitamin that provides nutrients close to the recommended daily intake should not cause serious side effects long-term [1.3.2]. However, some multivitamins, especially those marketed for specific purposes like eye health, may contain high doses of certain nutrients like beta-carotene, which can be risky for smokers [1.6.2]. It's always best to consult a doctor.

Daily calcium supplements may not be safe for everyone long-term. High intake is associated with an increased risk of kidney stones and may cause gastrointestinal side effects like constipation and bloating [1.7.4, 1.2.2]. Some conflicting research has also linked high supplemental calcium intake to an increased risk of cardiovascular disease [1.7.5].

The primary long-term risk of St. John's Wort is its potential to interact with a wide array of prescription medications, including antidepressants, birth control pills, and heart medications, making them less effective [1.2.5]. It can also cause a life-threatening condition called serotonin syndrome when taken with certain antidepressants [1.4.4].

Kava is linked to a significant risk of severe liver injury, including hepatitis, cirrhosis, and liver failure, even with short-term use [1.5.4, 1.9.3]. Due to over 25 reports of adverse events in other countries, the U.S. FDA has issued a consumer advisory about this potential risk [1.5.2]. Scientific evidence does not support its long-term use [1.5.3].

You should only take iron supplements if you have a diagnosed deficiency and are directed by a doctor. Long-term use of high-dose iron supplements can be toxic, leading to organ damage, and can interfere with zinc absorption [1.8.1, 1.8.3]. Men and postmenopausal women should generally avoid iron supplements unless medically necessary [1.3.2].

Multiple studies have shown that high-dose beta-carotene supplementation (20-30 mg per day) is associated with a significantly increased risk of developing lung cancer in current smokers and people with a history of asbestos exposure [1.6.1, 1.6.2, 1.6.3]. It is safer for this population to obtain beta-carotene from food sources.