Food supplements are popular, but they’re not always as safe as people think. This review explains that supplements sold in Denmark don’t have to be tested for safety before they’re sold. Problems can happen when supplements have too much of an ingredient, contain things that haven’t been studied much, or mix badly with medicines you’re already taking. The good news is that if a supplement makes you feel sick, you can report it to health officials so they can investigate and warn others.

The Quick Take

  • What they studied: How food supplements can cause harmful side effects and why these problems happen
  • Who participated: This is a review article that looked at information about supplement safety rather than testing people directly
  • Key finding: Supplements can cause problems through high doses, untested ingredients, mixing with medications, or being contaminated with unlisted substances
  • What it means for you: Before taking any supplement, talk to your doctor or pharmacist, especially if you take other medicines. If a supplement makes you feel sick, report it to health authorities so others can be protected

The Research Details

This is a review article, which means researchers looked at existing information about supplement safety problems rather than doing their own experiment. They examined why supplements can cause harm and what people should know about reporting problems. The review focuses on the Danish system for tracking supplement side effects, but the safety issues apply everywhere supplements are sold.

The researchers identified several ways supplements can hurt people: when they contain too much of an active ingredient, when they include substances that haven’t been properly tested for safety, when different ingredients interact badly with each other, when they’re mixed with things that make the body absorb them too quickly, when they clash with prescription medicines, or when they’re contaminated with unlisted substances.

Understanding why supplements cause problems is important because many people assume supplements are automatically safe just because they’re ’natural’ or sold over-the-counter. This review shows that’s not always true. It also explains how people can help protect others by reporting bad reactions, which helps health officials identify dangerous products.

This is a review article that summarizes existing knowledge rather than a study that tests people directly. It’s based on the Danish regulatory system and real-world reports of supplement problems. The information is reliable for understanding the types of problems that can occur, though it doesn’t provide statistics on how common these problems are.

What the Results Show

The review identifies six main ways supplements can cause harm. First, supplements sometimes contain doses that are too high for safe use. Second, some supplements include ingredients that haven’t been thoroughly studied for safety in humans. Third, when multiple ingredients are combined, they can interact in unexpected ways that cause problems. Fourth, some supplements include additives designed to make the body absorb ingredients faster, which can increase the risk of side effects.

Fifth, supplements can interact dangerously with prescription medications you’re already taking—this is especially important for people with health conditions. Sixth, some supplements are contaminated with unlisted substances, either by accident or on purpose, which can cause unexpected reactions.

The review emphasizes that in Denmark (and many other countries), supplements don’t have to prove they’re safe before being sold. This is different from prescription medicines, which must go through rigorous testing. This means problems might not be discovered until people start using the product and report bad reactions.

The review highlights that reporting systems are important tools for catching supplement problems. When people report bad reactions to health authorities, it helps identify dangerous products and warn others. The Danish system allows people to report suspected problems through the Veterinary and Food Administration’s website. This type of reporting helps create a safety net for supplement users.

This review confirms what other research has shown: supplements can cause real health problems, and many people don’t realize the risks. The specific causes identified here—high doses, untested ingredients, drug interactions, and contamination—are well-documented problems in supplement safety research worldwide. The emphasis on reporting systems aligns with how other countries are trying to improve supplement safety.

This review doesn’t provide numbers on how many people are harmed by supplements or how common each type of problem is. It focuses on the Danish system, though the safety issues apply globally. The review describes what can go wrong but doesn’t rank which problems are most serious or most common. It also doesn’t evaluate specific supplements or brands.

The Bottom Line

Talk to your doctor or pharmacist before starting any supplement, especially if you take prescription medicines (moderate confidence). Check the ingredient list and dose carefully (high confidence). Buy from reputable companies that test their products (moderate confidence). If a supplement makes you feel sick, stop taking it and report it to health authorities (high confidence). Don’t assume ’natural’ means ‘safe’—many natural substances can be harmful (high confidence).

Everyone who takes supplements should understand these risks, but especially: people taking prescription medicines, pregnant women, children, older adults, and people with health conditions. If you only take occasional vitamins from trusted brands at normal doses, your risk is lower, but you should still be aware of these issues.

Supplement side effects can happen quickly (within hours or days) or develop slowly over weeks. Some problems appear only after long-term use. If you notice any unusual symptoms after starting a supplement, report it right away rather than waiting to see if it gets worse.

Want to Apply This Research?

  • Log all supplements you take (name, dose, brand, start date) and note any symptoms that appear within 48 hours of starting something new. Include energy level, digestion, sleep, mood, and any physical symptoms.
  • Before adding any new supplement, use the app to check if it might interact with medicines you’re already taking. Create a reminder to discuss all supplements with your doctor at your next appointment.
  • Keep a running log of all supplements and any side effects. If you notice a pattern (like headaches always appearing 2 hours after taking a supplement), share this information with your doctor. Track which supplements you’ve tried and how you felt on each one.

This review provides general information about supplement safety and should not replace professional medical advice. Always consult with your doctor or pharmacist before starting any supplement, especially if you take prescription medicines, are pregnant, nursing, or have health conditions. If you experience symptoms you believe are caused by a supplement, stop taking it and contact your healthcare provider immediately. Report suspected supplement problems to your local health authorities. This information is educational and not a substitute for personalized medical guidance.