These Are the Supplements You Should Avoid Taking Together

Key Takeaways

  • Most adults in the U.S. take dietary supplements, including multivitamin-mineral supplements, vitamin D, and omega-3 fatty acid supplements.
  • If certain supplements are taken together, experts say it can lead to decreased effectiveness, increase the risk of side effects, or even cause potential harm to your health.
  • You should talk with a healthcare provider before taking any supplements to see if it’s safe, especially if you have a certain health condition or are taking specific medications.

More than half of adults in the United States take some kind of supplement or vitamin daily. Depending on the supplement you take, some claim to fill nutrient gaps in your diet and lifestyle while others aim to fight off deficiencies, lower the risk of certain diseases, strengthen specific parts of your body, or support overall health.

While supplements can offer a variety of potential health benefits, experts say it’s important to use them wisely and consider the timing of their intake. For example, taking all of your supplements at once after a meal or at a specific time of the day can impact their potency or absorption rates or even cause dangerous health effects.

“Certain supplements can interact with each other, leading to decreased effectiveness, increased risk of side effects, or potential harm to your health,” Danielle Crumble Smith, RDNa certified registered dietitian at Top Nutrition Coachingtold Verywell.

Other experts say people should use supplements with caution, especially since they are not regulated by the Food and Drug Administration (FDA) and most are not vigorously studied.

“Some supplements may have inconsistent ingredients and doses from batch to batch,” Marilyn Tan, MDdouble board certified in endocrinology and internal medicine and a clinical associate professor of medicine at Stanford University School of Medicine, told Verywell in an email.

Tan said that manufacturers also frequently make health claims that have not been well-studied in randomized controlled trials. In addition, some supplements can cause harm even though they are considered “natural.”

If you take any supplements or plan to add some to your lifestyle, here are combinations you should look out for and avoid mixing, according to experts.

Supplements Combinations That Can Decrease Effectiveness

According to Crumble Smith, there are certain supplements that shouldn’t be taken together because one can negate the effectiveness of the other.

  • Calcium and iron: These two supplements should not be taken at the same time because calcium can reduce the absorption of iron—iron can often become less effective when combined with other foods. If you need to take both calcium and iron supplements, try taking them at least two hours apart, Crumble Smith said. It might be easier to remember taking one in the morning and the other during the evening.
  • Zinc and copper: Both of these supplements compete for absorption in the body, so taking them together can reduce their effectiveness. If you need both, look for an option that contains a balanced ratio of zinc and copper, or take them at different times of the day, at least two hours apart.
  • Magnesium and calcium: These supplements can also interfere with each other’s absorption in the intestines when taken together, which can reduce their effectiveness. If you take both, take them at different times of the day.
  • Vitamin C and vitamin B12: These supplements should not be taken in high doses together because vitamin C can decrease the amount of vitamin B12 that the body absorbs and metabolizes. It’s recommended to take these supplements separately or at least two hours apart.

It’s important to note that the order in which supplements are taken can affect how well they are absorbed in the body and how effective they are, Mary Sabat, RDN, LDa registered dietitian nutritionist and an ACE-certified trainer, told Verywell in an email. For example, some supplements like calcium are best taken with food to enhance absorption, while others like iron are better absorbed when taken on an empty stomach.

Supplements Combinations That Can Be Harmful to Your Health

  • Vitamin C and iron: Vitamin C can enhance the absorption of iron in the body, which can be a good thing. However, if vitamin C is taken in high doses, it can lead to excess levels in the body and increase the risk of iron toxicity. If you must take both, experts generally recommend spacing them out by at least two hours.
  • Vitamin D and calcium: While these two supplements are often recommended together, taking high doses of both can lead to hypercalcemiaor too much calcium in the blood. This can increase the risk of kidney stones or heart issues.

What About Powders Containing Multiple Vitamins and Supplements?

Experts say it’s also important to pay attention to powders and other products that contain various supplements, including protein powders, gummies, energy drinks, or bars. That’s because some of the ingredients in these products may not work well together or could pose health risks when combined with other things, Crumble Smith said.

For example, some people may blend athletic powders or caffeine with herbs, stimulants, and supplements like Ashwagandha and Rhodiola. In the short-term, mixing these things can provide an energy boost. But there may be health risks associated with long-term use.

“Rhodiola is really common and you’ll see that in products in combination with caffeine,” Crumble Smith said. said. “In the long-term, if this is something that people are taking on a consistent basis, it could stress the adrenal gland. People might experience adverse symptoms like anxiety, insomnia, or even heart palpitations.”

Whatever powder or supplement blend you decide to use, be sure to look at all of the active and inactive ingredients and check for any FDA warnings, Tan said. You may also want to inform your healthcare provider about all of the supplements you are taking, including pills, liquids, powders, and topical creams.

What to Know Before Taking Supplements

Before you decide to take any supplements, experts suggest consulting with your healthcare provider to determine the best options for your individual needs. This is especially important for people with pre-existing medical conditions or those who are taking medications.

“Supplements are great, but they’re not meant to replace balanced eating, sleep, or exercise,” Crumble Smith said. “If you want to take supplements, first address those basics like sleep, hydration, eating well, and exercise. Then you can meet with a healthcare provider or dietitian and figure out where there might be gaps where supplementation could help.”

What This Means For You

If you are taking supplements or plan to add any to your lifestyle, experts recommend talking with your healthcare provider first. A professional can help determine which supplements you should avoid mixing and which ones you shouldn’t take if you’re on certain medications.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

  1. Mishra S, Stierman B, Gahche JJ, Potischman N. Dietary supplement use among adults: United States, 2017-2018. NCHS Data Brief. 2021;(399).

  2. National Institutes of Health. Should you take dietary supplements?

  3. Food and Drug Administration. Mixing medications and dietary supplements can endanger your health.

  4. Food and Drug Administration. FDA 101: dietary supplements.

  5. National Library of Medicine: MedlinePlus. Taking iron supplements.

  6. Icahn School of Medicine at Mount Sinai. Zinc.

  7. Dai Q, Shu XO, Deng X, et al. Modifying effect of calcium/magnesium intake ratio and mortality: a population-based cohort study. BMJ Open. 2013;3(2):e002111. doi:10.1136/bmjopen-2012-002111

  8. University of Rochester Medical Center. Vitamin C.

  9. Oregon State University. Micronutrient information center – vitamin C.

  10. National Institutes of Health Office of Dietary Supplements. Vitamin D: fact sheet for health professionals.

By Alyssa Hui

Alyssa Hui is a St. Louis-based health and science news writer. She was the 2020 recipient of the Midwest Broadcast Journalists Association Jack Shelley Award.