Supplements get a lot of buzz these days—and it’s not for no reason. Many of them can offer real benefits to your wellbeing, including better sleep, less stress, or a healthier gut. But not all supplements are created equal. It’s important to keep in mind that they all come with risks, and some can be more dangerous than others, especially when combined with other supplements or prescription medications. Staying aware of any potential interactions is crucial to keeping your health and safety in great shape.
To shed some light on a few common supplements that can be especially harmful with combined with other medications, we spoke to pharmacy doctor and the VP of Pharmacy and Medical Operations at Eden, Dr. Rebecca Emch. She warned against vitamin K, fish oil, calcium, and St. John’s wort. Learn more about the risks of each below.
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1. Vitamin K
Vitamin K is known for supporting bone health by working with calcium to keep bones strong. Others may use it to help maintain heart and artery health, as it may assist in preventing calcium from building up in blood vessels. However, when taken in high doses, it can become dangerous for those on blood thinners.
"Vitamin K, especially at high doses, can interfere with Coumadin (warfarin) and other blood thinners because it directly affects clotting factors targeted by the medication," explains Dr. Emch. "This is a classic interaction but too often overlooked, especially when people start new greens-based powders, superfood blends, or fortified shakes, not realizing they're getting concentrated Vitamin K."
2. High Doses Of Fish Oil
Many people take fish oil because it's a convenient source of omega-3 fatty acids, and therefore supports heart and brain health. It can also help reduce inflammation in the body, which is why some people use it for their joints. Others take it to support healthy cholesterol levels and overall wellness, and it tends to be more popular amongst an older crowd.
"Fish oil (high-dose) supplements can thin your blood," says Dr. Emch. "That can become problematic if someone is taking anticoagulant or antiplatelet medications, like warfarin, clopidogrel, or newer direct oral anticoagulants. The risk isn't that fish oil is toxic; the risk comes from compounding effects leading to bruising, nosebleeds, or increased bleeding time. It's worth reviewing dose and need with a trusted clinician."
3. Calcium
Calcium is an incredibly important mineral that all of our bodies need to function. It keeps our bones, teeth, and muscles strong, and assists our nerve functions. However, before you supplement it, you should double-check with your doctor if that's a safe idea.
"Calcium, when taken too close to certain prescription medications, particularly iron supplements, thyroid hormones like levothyroxine, and some antibiotics, can interfere with how your body absorbs those medications," notes Dr. Emch. "This doesn't mean calcium is 'bad,' but the timing matters. Even something as simple as a morning calcium supplement could unintentionally reduce the effectiveness of a thyroid medication if taken together."
4. St. John's Wort
People often take St. John's Wort because it may help with mild, occasional low mood and stress. Some people use it as a natural option to support emotional balance or improve overall well-being. It's also been used traditionally to help with sleep and relaxation, but it should be used with caution.
"St. John's Wort is a common herbal remedy for mild depression, but it significantly induces liver enzymes that metabolize many medications, including SSRIs, birth control, blood thinners, seizure medications, and even some heart and cancer treatments," explains Dr. Emch. "Taking St. John's Wort with prescription medication can either reduce those medications' effectiveness or, in some cases, dangerously increase the side effects, depending on how the active drug is processed. It's one of the most well-documented supplements with serious potential for interaction and should never be combined with prescriptions without medical oversight."
The moral of the story with all these supplements, and any supplement you might want to start taking, is that you should always speak to your doctor about whether or not you need them, and if they would interfere with any medication you're already on.
