Research reveals most Americans don't know the risks: here, experts list some vitamins, supplements, and medications not to take together.
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Supplements to avoid with medication
Some supplements change how well a prescription medication is absorbed, used, and eliminated in the body. This can reduce the effectiveness of a medication or, in some cases, increase the risk of side effects.
If you take blood thinners
Some vitamins and supplements can interfere with blood-thinning medications, says Robert Glatter, MD, an attending physician in the department of emergency medicine at Lenox Hill Hospital in New York City. “Just because something is natural doesn’t mean it is risk-free,” he adds.
Dr. Glatter points to several supplements that can raise your bleeding risk if you take a daily aspirin or a blood thinner like Coumadin (warfarin). “[These supplements] can cause bleeding episodes after a fall or injury, and there’s a high risk of internal bleeding”:
- Feverfew
- Fish oil
- Garlic
- Ginger
- Ginkgo biloba
- Vitamin E
- White willow bark
Other herbs and vitamins actually reduce the effectiveness of blood thinners, such as echinacea, a popular cold remedy. “This is a big one to be aware of,” Dr. Glatter says.
People taking blood thinners also need to watch vitamin K intake from foods such as kale, lettuce, broccoli, and chickpeas. Unlike most supplement-drug interactions, which can occur from high concentrations of an ingredient, this is one of the most common food-drug interactions.
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If you take diabetes meds
As a general warning, the National Center for Complementary and Integrative Health (NCCIH) says that some dietary supplements have been linked to kidney disease. Diabetes is the leading cause of kidney disease, and so it’s extra important to only take supplements under medical supervision.
Certain supplements can interfere with diabetes medications, according to the NCCIH:
- Berberine may cause your blood sugar to drop too low.
- St. John’s Wort can interfere with how diabetes drugs are broken down, leading to a buildup in the body.
- Herbal supplements such as cinnamon or aloe may cause side effects when combined with diabetes medications.
Dr. Glatter also points to Coenzyme Q10 (CoQ10), a supplement used to support heart health. “CoQ10 can also lower blood sugar, and if you are taking other diabetes drugs, you run the risk of developing low blood sugar,” he says.
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If you take blood pressure meds
Coenzyme Q10 (CoQ10) can also lower blood pressure. “In combination with blood pressure medications, this can cause dangerously low blood pressure,” Dr. Glatter says. “This can happen out of the blue, often after you have been taking CoQ10 for six to eight weeks, and it could precipitate a fall or head injury.”
The American Heart Association (AHA) adds that these herbal supplements might interact with blood pressure medications:
- Grapefruit
- Ginseng
- Licorice root
- St. John’s Wort
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If you take antidepressants
St. John’s Wort is an herbal remedy sometimes used for mild to moderate depression. But if you combine it with a prescribed antidepressant—like an SSRI—it can actually worsen symptoms such as anxiety and confusion, according to Dr. Glatter.
Both antidepressants and St. John’s Wort raise levels of the feel-good brain chemical serotonin, which can backfire. (Supplements like SAMe and 5-HTP have a similar effect.) “This can cause serotonin syndrome and in severe cases, it may lead to muscle rigidity and seizures,” he says.
While more research is needed, other “mood-boosting” supplements may interact with antidepressants, too, according to 2023 research in Frontiers in Pharmacology. Make sure to talk to your doctor before taking popular adaptogens such as:
- Ashwagandha
- Ginseng
- Maca
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If you’re on antibiotics
Taking antibiotics—especially those in the tetracycline family—along with iron supplements can dampen the effects of the antibiotics, making them less likely to work, Dr. Glatter says. Spacing them out by at least two hours will help.
According to the Linus Pauling Institute at Oregon State University, other supplemental minerals can have this effect, too, including:
- Calcium
- Magnesium
- Manganese
- Zinc
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Supplement combos to avoid
Supplements can interact with prescription drugs, but some don’t play well with each other, either. Taking certain vitamins, minerals, or herbs at the same time can block the benefits or even trigger side effects you weren’t expecting.
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Multiple minerals
“Taking large amounts of minerals with other minerals will reduce absorption,” says Tod Cooperman, MD, founder and president of ConsumerLab.com, an independent testing company focused on health and nutrition products. In essence, the minerals compete with one another and both lose out. To maximize benefits, space out mineral supplements by at least two hours, Dr. Cooperman advises.
Dr. Cooperman points to a few specific examples:
- Magnesium and calcium
- Potassium and calcium
- Zinc and copper
He highlights that zinc not only blocks copper absorption, but long-term high-dose zinc may even trigger copper deficiency.
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Iron and some plant-based antioxidants
Iron is essential for carrying oxygen to your cells, which fuels your energy. But certain plant-based compounds—including those in green tea, black tea, and curcumin supplements—can block your body from absorbing iron.
That doesn’t mean you have to give up your matcha or turmeric, but it does mean you should separate them from your iron supplement, says Dr. Cooperman. Like minerals, space these out by a couple of hours.
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Fish oil and Ginkgo biloba
Omega-3 fish oil supplements may tame inflammation and improve your mood, but when you take these supplements with herbs that thin the blood—such as ginkgo biloba or garlic—they may prevent clotting and can lead to uncontrolled bleeding, Dr. Cooperman says. To be safe, split them up by at least two hours.
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Melatonin and other sleep aids
You can easily overdo herbs or supplements with sedative properties. These include melatonin, valerian, ashwagandha, kava, and St. John’s Wort: “When taken together, they can cause too much sleepiness,” Dr. Cooperman says. Always read the labels to find out what you can expect from supplements.
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Red yeast rice and vitamin B3
The American Medical Association reports that nearly 94 million Americans have “borderline” high cholesterol, and many might seek out natural cholesterol-lowering options such as red yeast rice or niacin (vitamin B3). These don’t play well together, however.
“Doubling up doesn’t increase the benefits and may be harmful to the liver,” says Todd Sontag, DO, a family medicine specialist with Orlando Health Physician Associates in Florida. When prescription cholesterol-lowering drugs are added to the mix, your risks can increase. Be sure you’re aware of niacin flush and what you can do about this potential side effect.
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Vitamins A, D, E, and K
Vitamins A, D, E, and K are all fat-soluble vitamins, which means taking them together can reduce absorption—similar to combining minerals. “If you take a multivitamin, don’t worry,” Dr. Cooperman says. “But if you are K-deficient and need extra K, take it two hours apart from the other fat-soluble vitamins.” Believe it or not, vitamin K is one of the nutrients even nutritionists don’t get enough of.
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Adaptogen blends
Adaptogens are natural, usually plant-derived substances that have been used in traditional medicine for centuries. In recent years, they’ve gained popularity for potential benefits such as stress management, immune support, and hormonal balance—and some studies do support certain adaptogenic benefits, according to the Cleveland Clinic.
However, a 2025 review of research in Frontiers in Pharmacology highlights how the safety of adaptogens—especially when combined—is still not well understood. The researchers found that multi-ingredient adaptogenic supplement blends were frequently associated with adverse side effects, including stomach issues, liver damage, skin reactions, allergic reactions, and mood changes.
There are dozens of different adaptogens, but some common ingredients in blends may include:
- Ashwagandha
- Astragalus
- Brahmi
- Ginseng
- Propolis
- Reishi or Cordyceps mushrooms
- Rhodiola rosea
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Sources
- Tod Cooperman, MD, president of consumerlab.com, White Plains, New York
- Tod Sontag, DO, family medicine specialist, Orlando Health Physician Associates, Orlando, Florida
- Robert Glatter, MD,assistant professor of emergency medicine, Northwell Health, New York, New York
Medically reviewed by 
