7 Supplement Combos You Should Never Take Together, According to Dietitians

Grocery stores are full of supplements that claim to help with things like preventing colds, improving mood, and reducing stress. Because of these promises, supplements have become more popular, with many people taking several each day. But taking some supplements together can cause problems. They might cancel each other out or stop your body from absorbing them properly. Some combinations can even cause bad health effects. It’s important to be careful with which supplements you mix. Here are seven combinations you should avoid or be careful about.

1. Zinc and Calcium

Zinc and calcium compete for absorption in the gut, so taking them together can make both less effective, says dietitian Alyssa Simpson. Zinc helps support immune health and wound healing, while calcium is important for bone health. But if your body can’t absorb them well, they won’t give you the full benefits. To avoid this, Simpson suggests taking zinc and calcium supplements at least two hours apart. This way, your body can absorb both properly and you’ll get the most out of each one.

2. Iron and Zinc

Iron can lower the absorption of zinc when taken together, says Elizabeth Harris, M.S., RDN. This is especially true for iron supplements that contain 25 milligrams of iron or more. While high doses of iron are often used to treat iron deficiency, they can interfere with zinc absorption. This can lead to lower zinc levels in the body. If you take both supplements, it’s important to separate them. Harris recommends waiting at least two hours between taking zinc and iron supplements. This will help ensure your body absorbs both nutrients properly. By spacing them out, you can avoid lowering zinc levels.

3. Iron and Calcium

Calcium can make it harder for your body to absorb nonheme iron, the type of iron found in supplements and plant foods, says dietitian Carla Hernandez. While this effect isn’t certain, research shows it’s likely. This can be a problem if you’re trying to fix an iron deficiency. To avoid this, Hernandez suggests taking calcium and iron supplements at least two hours apart. This will help your body absorb both nutrients better. By waiting, you can make sure you get the full benefits of each supplement.

4. Magnesium and Zinc

Magnesium and zinc compete for absorption in the intestines, so taking large doses of both together can limit how much your body absorbs, says Hernandez. This is especially true for very high doses of zinc (over 140 mg per day), which is much higher than the recommended limit of 40 mg for adults.To avoid this, your healthcare provider might suggest spacing out these supplements. Hernandez recommends taking magnesium and zinc at different times of the day—magnesium in the evening and zinc in the morning. Zinc is best taken with food to avoid nausea. Magnesium glycinate is a good choice for nighttime since it can help with relaxation and sleep.

5. St. John’s Wort and Serotonergic Supplements 

St. John’s wort is an herbal supplement often used for managing depression, though research on its effectiveness is still unclear. It may increase serotonin levels, so it shouldn’t be taken with antidepressants, as this could dangerously raise serotonin levels. There are also risks when combining St. John’s wort with other serotonin-boosting supplements, like 5-HTP or SAMe. This can cause too much serotonin in the body, leading to symptoms like restlessness and confusion. To stay safe, it’s best to use only one serotonin-supporting supplement at a time. Always check with your healthcare provider before starting any of these supplements for personalized advice.

6. Ginkgo Biloba and High-Dose Fish Oil 

Ginkgo biloba and high-dose fish oil can thin the blood, which increases the risk of bleeding when taken together, says Simpson. This is especially risky if you’re also taking blood-thinning medications like warfarin, adds Angie Konegni, M.S., RD, CSR, LD. Other supplements that can thin the blood include aloe, garlic, ginger, turmeric, fenugreek, and ginseng. Taking these with ginkgo biloba or fish oil can raise the chances of bleeding. To stay safe, Simpson recommends spacing out the supplements or using smaller doses. This helps lower the risk of thinning the blood too much. It’s important to always check with your healthcare provider before combining any of these supplements. Doing so will ensure they’re safe and won’t cause any harmful side effects. Being cautious with supplements can help protect your health and avoid complications.

7. St. John’s Wort and Ginseng

St. John’s wort helps with depression by increasing serotonin levels, and ginseng can do something similar. Taking both together might cause problems. “Both affect mood and energy, but combining them could overstimulate the nervous system,” says Konegni. This could lead to symptoms like agitation, a fast heart rate, or even serotonin syndrome, a dangerous condition. To stay safe, it’s important not to take St. John’s wort and ginseng together without checking with a healthcare provider. Always talk to your doctor before using both to make sure it’s safe for you. This will help avoid any harmful side effects.