5 Supplements, Health Experts Say, Make Medicines Less Effective

Reviewed by Dietitian Karen Ansel, MS, RDN

Key points

• Some supplements can interact with certain medications and reduce their effectiveness.

• Top offenders include calcium, magnesium, iron, fiber, activated charcoal, and vitamins C and K.

• If you take supplements, talk to your doctor to make sure they are safe for you.

If you’re looking to improve your health routine, you may want to consider a supplement. Or maybe even get one now. While supplements are generally sold over the counter, that doesn’t mean they don’t carry risks. And one to watch out for is drug interactions, which can decrease the effectiveness of your medication.

For example, some vitamin and mineral supplements can interfere with the absorption of medications. Other supplements can bind to drugs, preventing the drug from being used in the body, or they can be metabolized in the same or similar ways as drugs, explains naturopathic doctor Jacob Wolf, ND, LAc, Dipl. MAN. This can have a dangerous impact on your health.

What supplements should be on your radar? To find out, we talked to the experts. Here are five supplements that say they could reduce the effectiveness of your medication.

1. Calcium, Magnesium and Iron

Minerals such as calcium, magnesium and iron can bind to drugs, especially levothyroxine, a drug used to treat hypothyroidism, Wolf says. This can affect how levothyroxine is used in the body, adversely affecting treatment, he says.

These minerals can also interact with tetracycline and fluoroquinolone class antibiotics, says pharmacist Amanda Corbett, Pharm.D., BCPS, FCCP, FAIHM. Taking these mineral supplements at the same time as antibiotics can reduce the bioavailability of the antibiotic, creating risks such as bacterial resistance or ineffective treatment.

When you get a new prescription, Corbett recommends checking with your pharmacist before taking any mineral supplements, including multivitamins or multimineral formulations. For antibiotics, be sure to ask if you should make temporary adjustments to your supplement routine. With levothyroxine, a rule of thumb is to avoid taking these minerals within four hours of taking the medication. However, it’s a good idea to check with your healthcare provider to be sure.

2. Fiber

Fiber is an important nutrient for digestive regularity, healthy cholesterol levels, blood sugar management, and more. You can find fiber in plant foods such as fruits, vegetables, beans, lentils, and whole grains. You can also get it from supplements. However, as good for you as fiber is, supplementing isn’t always a great idea because high doses can affect the absorption of certain medications.

One of note is the diabetes drug metformin. Emerging research suggests that taking a fiber supplement with metformin may affect this drug’s ability to lower blood sugar. If you’re wondering about dietary fiber, don’t worry. High-fiber foods are the cornerstone of blood sugar management, even for those taking blood sugar-lowering medications such as metformin.

Fiber can also affect the effectiveness of other medications, including digoxin (which treats certain heart conditions) and levothyroxine for hypothyroidism, Wolf points out. If you choose to take a fiber supplement, Wolf recommends talking to your healthcare provider about spacing out your fiber and medication doses.

3. Activated charcoal

Activated charcoal is a form of charcoal that is used in the emergency room to treat the ingestion of toxic drugs and poisons. It is also sold in over-the-counter supplements to help you detox. Although it can absorb toxic substances when used properly in a medical setting, at home it can have harmful effects. “Activated charcoal acts like a sponge and can bind to many medications. It’s best to avoid activated charcoal altogether if you’re taking any life-critical medications,” says Wolf.

4. Vitamin C

Vitamin C is an important antioxidant that protects cells from free radical damage and supports the proper functioning of the immune system. However, if you’re undergoing chemotherapy for cancer, experts strongly caution against taking vitamin C supplements. “Vitamin C can make certain chemotherapy treatments less effective or ineffective in treating cancer,” says Corbett. Vitamin E, another antioxidant, may also interfere with the effectiveness of chemotherapy.

5. Vitamin K

Vitamin K is a fat-soluble vitamin that helps blood clot and supports bone health. However, vitamin K can reduce the effectiveness of a blood-thinning drug called warfarin (Coumadin). This, in turn, can cause the blood to clot, which can lead to a heart attack or stroke. If you’re taking warfarin, you don’t necessarily need to avoid vitamin K, but it’s essential to keep the amount you’re getting — both from food and supplements — consistent to avoid clotting problems.

Tips for taking supplements safely

• Check with your healthcare provider. Just because supplements are sold over the counter doesn’t mean they’re benign. Many supplements can interact with medications, so it’s essential to check with your prescribing healthcare provider to make sure the supplements you’re taking work well with your medications. Your pharmacist can also be a valuable resource, so talk to them as well.

• Choose quality supplements. Look for ones that have been independently tested in a lab, Corbett advises. “Testing should confirm that the ingredients on the dietary supplement label are indeed the ingredients [in the product] and the product should have safe levels of heavy metals,” she says. Products should also have no added drugs, which independent testing also looks for. Trusted independent testing organizations include ConsumerLab, NSF, and the US Pharmacopeia (USP).

• Find out how much to take. Supplement dosages are listed on the label, but are not standardized. This means that they can vary from product to product and far exceed safety levels. Rather than assuming that the dose on the label is the right amount, it is better to ask your healthcare provider about the dose that is right for you.

Our expert

Certain supplements can interact with medications you take, potentially making them less effective. Some of the biggest troublemakers include calcium, magnesium, iron, fiber, activated charcoal, and vitamins C and K. But that’s just the short list. Before adding any supplement to your routine or starting a new medication, talk to your doctor about possible interactions. They can tell you if the supplement is safe for you and, if so, how much to take and the best time of day to take it.

Read the original article on EatingWell