With more people turning to supplements to boost their health, it's easy to assume that combining a few vitamins or herbal remedies is harmless. But, doctors and health experts warn that certain supplement pairings can do more harm than good—leading to reduced effectiveness, dangerous interactions, or even serious health risks.
Some supplements work well together, but others can amplify side effects or interfere with absorption, potentially leading to larger health issues, explains Azza Halim, MD, a board-certified anesthesiologist specialized in anti-aging and regenerative medicine. That's why it's so important to have your doctor or pharmacist review your supplement regimen before you start taking any new ones. What's more, the timing of certain doses can matter, too.
From popular pairings that cancel each other out to specific combinations that could put your health at risk, knowing what not to mix is just as important as knowing what to take. Read on to discover the 12 supplement combos that doctors say should never be taken together.
RELATED: 21 Surprising Signs You Have a Vitamin Deficiency
1 | Calcium and iron
iStockOne of the most common reasons that supplements might make a poor pairing is if they cancel one another out. Trista Best, MPH, RD, a registered dietitian at Balance One Supplements, says that calcium and iron are a perfect example of how you can undermine the benefits of supplements by combining the wrong things.
"You'll want to avoid taking your iron supplement with a calcium supplement or food source," says Best. "These two vitamins compete for absorption, and calcium will reduce the amount of iron your body is able to absorb—if any."
To maximize your body's absorption of an iron supplement, Best recommends pairing it with vitamin C. And, it doesn't need to come in a pill form.
"Non-heme iron comes from plant sources and it isn't absorbed as easily as heme forms, but adding vitamin C can increase iron's absorption. This can be done simply by adding lemon to your water or eating some strawberries along with your supplement regimen," she says.
2 | Zinc and copper
iStockMany people favor zinc and copper supplements to boost their immune systems. However, certified nutritionistJenny Dobrynina says that taking them at the same time will produce ineffective results.
"Combining copper and zinc is not advisable because they compete for absorption in the body. So, taking them together reduces their effectiveness," she says.
RELATED: 10 Best Supplements for Weight Loss
3 | Vitamins C and B-12
10 Surprising Signs You Have a Vitamin C Deficiency, According to DoctorsShutterstockDobrynina also warns against taking vitamin C and vitamin B-12 at the same time: "I recommend taking these two supplements at least two hours apart."
According to the Mayo Clinic, taking these two supplements simultaneously can lead to reduced levels of vitamin B-12 in the body. A B-12 deficiency can cause anemia, or a reduction in healthy red blood cells, which can lead to fatigue, breathlessness, balance problems, memory impairment, or other health issues.
4 | Vitamins E and K
2 | Vitamin EPeopleImages / iStockTaking Vitamins E and K shouldn't be taken at the same time since they can have opposing effects on coagulation, Dobrynina warns.
"Studies show that vitamin E supplementation leads to increased bleeding in some people, " she explains. "Doctors usually prescribe vitamin K supplements to help with blood clotting. So, taking vitamin E simultaneously with vitamin K can counteract the effects of vitamin K."
A 2023 case study published in the Journal of Medical Case Reports found that high doses of vitamin E can "inhibit vitamin K-derived coagulation factor synthesis, which can cause serious bleeding events such as gastrointestinal bleeding and intracranial hemorrhage."
RELATED: 10 Surprising Vitamin Deficiency Causes Revealed by Doctors
5 | Fish oil and ginkgo biloba
iStockJacek Szymanowski, a Precision Nutrition-certified nutritionist and health coach, says that the combo of fish oil and ginkgo biloba can also affect your blood's ability to clot safely.
"Combining these can increase the risk of bleeding due to their blood-thinning effects," she says. "Both supplements have anticoagulant properties, which can synergistically increase bleeding risk, especially in high doses or with other blood thinners."
RELATED: 5 Surprising Benefits of Taking an Omega-3 Supplement
6 | Folic acid (vitamin B9) and vitamin B-12
1 | Vitamin B12iStockFinally, folic acid and vitamin B-12 is another pairing that you should re-evaluate with your doctor's help since "excess consumption of vitamin B9 and B-12 (folic acid and folate) can hide the symptoms of vitamin B-12 deficiency," says Dobrynina.
One study published in the Cochrane Database of Systematic Reviews found that "there is a risk that if folic acid is given to people who have undiagnosed deficiency of vitamin B12 it may lead to neurological damage."
A vitamin B12 deficiency can cause the same type of anemia as a folate deficiency, but it may also lead to permanent nerve damage. The researchers explain that while folic acid can fix the anemia caused by low B12, it won't stop the nerve damage from getting worse—potentially delaying diagnosis and treatment.
For the best and most personalized recommendations about which supplements you should and shouldn't take together, ask your doctor or pharmacist.
