Warning: Do Not Mix These Supplements

Even the most common supplements can have surprising interactions with drugs and other supplements.

"Things that are natural are not necessarily safe," says David S. Seres, MD, director of medical nutrition and associate professor of medicine at Columbia Medical Center. He explains that much of the reasoning for taking different supplements comes from looking at large populations that consume these substances through diet and seem to have positive health outcomes as a result. However, when a substance is put in supplement form, it's much more concentrated.

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"Consumers should not be surprised that there is the potential for interactions and toxicity when it comes to supplements," he says.

Here, a few supplements that can have potentially dangerous interactions with different medications and other herbal supplements.

Drug interactions: Taking fish oil with blood pressure-lowering drugs can increase the effects of these drugs and may lower blood pressure too much. You should also be careful of taking fish oil along with other medications that can increase risk of bleeding, such as aspirin, ibuprofen, or naproxen.

Supplement interactions: Taking high doses of fish oil with herbs that slow blood clotting (including Ginkgo bilboa) may cause bleeding.

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Drug interactions: Calcium can interfere with many medications, including prescription osteoporosis drugs known as bisphosphonates (such as alendronate), certain blood pressure medications, antibiotics in the tetracycline and quinolone families (like Cipro); and levothyroxine, which treats hypothyroidism.

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Drug interactions: Echinacea's ability to stimulate the immune system may interfere with drugs that decrease the immune system, such as the steroid prednisone.

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Drug interactions: Since melatonin may make you drowsy, taking it with sedative drugs (such as benzodiazepines, narcotics, and some antidepressants) may cause too much sleepiness. Melatonin may also slow blood clotting, so taking it with anticoagulant medications such as heparin or warfarin (Coumadin) may increase the chances of bruising and bleeding. Avoid using melatonin if you're taking medication to control blood pressure, as it may raise blood pressure.

Supplement interactions: Taking melatonin with other supplements that have sedative properties (including St. John's wort and valerian) may increase the effects and side effects of melatonin.

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Drug interactions: Taking St. John's wort with antidepressants may lead to too-high levels of serotonin in your body, which can result in serious side effects including muscle rigidity and seizures. St. John's wort may also make other medicines less effective, such as birth control pills, some HIV drugs, and blood thinners like Warfarin. It may also interact with common migraine medications such as sumatriptan and zolmitriptan and increase risk of serotonin syndrome.

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Drug interactions: Vitamin D might decrease the effectiveness of the cholesterol-lowering drug atorvastatin (Lipitor), and can also interfere with some high blood pressure medications. Taking high doses of D along with a diuretic medication may result in too much calcium in the body, which can cause kidney problems.

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Drug interactions: If you’re taking an antibiotic that contains quinolone or tetracycline, zinc supplements could make it more difficult for your body to absorb both the medicine and the zine. To ensure you get the right amount of your antibiotic, take it two hours before or four to six hours after you take a zinc supplement. The same is true for penicillamine drugs, which are often used for rheumatoid arthritis. Make sure to take zinc two hours prior to these types of medications to prevent poor absorption of penicillamine.

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