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How Dietary Supplements Can Interact with Your Prescription Drugs

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Photo: Towfiqu Photography / Getty Images

Reishi. Maca. Ashwagandha. Turmeric. Ho Shu Wu. CBD. Echinacea. Valerian. The herbal supplements on the market these days are infinite, and the claims sometimes feel larger than life.

While there are some proven nutritional and holistic benefits to these adaptogens and herbaceous remedies, did you know that they could potentially interfere with your prescription medication?

A recent study of older (age 65 and up) U.K. adults found that 78 percent of participants were using dietary supplements with prescription drugs, and almost one-third of participants were at risk for an adverse interaction between the two. Meanwhile, an older—but larger—study published in 2008 by the American Journal of Medicine found that almost 40 percent of their 1,800 participants were taking dietary supplements. In that pool of 700+ people, researchers found more than 100 potentially significant interactions between the supplements and drugs.

With more than half of Americans taking a dietary supplement of one kind or another, according to JAMAhow is this still flying under the radar? 

Why Supplements Can Interfere with Prescription Drugs

Much of this comes down to how things are processed in the liver. The liver is one of the main sites of breakdown for various medications, says Perry Solomon, M.D., president and chief medical officer of HelloMD. This organ—your body's detoxifying powerhouse—uses enzymes (chemicals in that help metabolize different substances) to process food, drugs, and alcohol that are ingested, making sure you absorb what your body needs and eliminating the rest. Certain enzymes are "assigned" to process certain substances.

If an herbal supplement is metabolized by the same enzyme that metabolizes other drugs, the supplement is then competing with those drugs—and it can mess with how much medication your body is actually absorbing, says Dr. Solomon.

For example, you've probably heard about CBD, a newly popular herbal supplement extracted from cannabis, and a potential culprit interfering with your prescription medication. "There is a major enzyme system called cytochrome p-450 system that is a major player in drug metabolism," he says. "CBD is also metabolized by this same enzyme system and, in high enough doses, it competes with other medication. This can result in the other medication not being metabolized at the 'normal' rate."

And it's not just CBD: "Almost all herbal supplements could have an interaction with prescription medications," says Jena Sussex-Pizula, M.D., at the University of Southern California. "They may directly inhibit the drug itself; for example, warfarin (a blood thinner) works by blocking the vitamin K used by blood clots. If someone were to take a vitamin or supplement that had high levels of vitamin K, it would directly inhibit this drug." Certain supplements can also alter the way medications are absorbed in your gut and excreted through the kidneys, says Dr. Sussex-Pizula.

How to Safely Take Supplements

Aside from interaction with prescription drugs, there are a lot of safety issues to consider before you take a dietary supplement. This all doesn't necessarily mean you should shy away from herbal supplements, though—they can be enormously helpful for some patients. "As a naturopathic doctor, herbal medicine is one of my most commonly used tools for treatment in both acute and chronic conditions," says Amy Chadwick, N.D., a naturopathic doctor at Four Moons Spa in San Diego. While some herbs and minerals can potentially interact with medication, "there are also herbs and nutrients that help support deficiencies or reduce the side effects of certain pharmaceutical medications," she says. (See: 7 Reasons You Should Consider Taking a Supplement)

From a western medicine perspective, Dr. Sussex-Pizula agrees that these supplements can be quite beneficial—as long as they're taken under supervision. "If there is research data suggesting a supplement can be helpful, I discuss it with my patients," she says. "For example, research continues to come out suggesting a benefit for turmeric and ginger in patients with osteoarthritis, and I have several patients supplementing their treatment plans with these medicinal foods, resulting in improved pain control." (See: Why This Dietitian Is Changing Her View on Supplements)

Luckily, for the most part, you probably don't need to be concerned: Whether it's in the form of tea or a powder you've added to a shake, you're likely taking an extremely low dose. "Most common herbs used in tea form or food form—such as a passionflower tea for calming [effects], green tea for antioxidant properties, or the addition of reishi mushrooms to a smoothie for adaptogenic support—are in a dose that is generally beneficial and not high or strong enough to interfere with the use of other medications," says Chadwick.

If you're doing something a little heavier duty than that—like taking a higher-dose pill or capsule—that's when you really need to see a doctor. "These [herbs] should be prescribed and used appropriately for individual people based on their specific needs, taking into account their physiology, medical diagnoses, history, allergies, as well as any other supplements or medications they are taking," says Chadwick. A good back-up: The free Medisafe app monitors your prescription and supplement intake and can alert you of possible dangerous interactions and remind you take your meds every day. (That's why some personalized vitamin companies are making doctors available to help make choosing supplements easier—and safer—than ever.)

Common Supplements with Drug Interactions

Should you be worried about anything you're taking? Here is a list of herbs to look out for that are known to interact with certain prescription medications. (Note: This is not a complete list nor a substitute for talking to your doctor).

St. John's wort is one you'll want to skip if you're on hormonal birth control pills, says Dr. Sussex-Pizula. "St. John's wort, used by some people as an antidepressant can actually dramatically reduces levels of certain medications in the blood such as birth control pills, pain medications, certain antidepressants, transplant medications, and cholesterol medications."

"St. John's wort should be avoided if taking antiretrovirals, protease inhibitors, NNRTIs, cyclosporine, immunosuppressive agents, tyrosine kinase inhibitors, tacrolimus, and triazole antifungals," says Chadwick. She also warned that if you've been taking an SSRI (selective serotonin reuptake inhibitor) or MAO inhibitor as prescribed by your health care provider, to skip herbs like St. John's Wort (which is known as a natural antidepressant).

Ephedra is an herb often touted for its weight-loss or energy-boosting benefits—but it comes with a long list of warnings. The FDA actually banned the sale of any supplements containing ephedrine alkaloids (compounds found in some ephedra species) in U.S. markets in 2004. "It can cause serious, even life-threatening, cardiac arrhythmias, mimic heart attacks, cause hepatitis and liver failure, induce psychiatric symptoms, and cut off blood flow to the intestines, causing bowel death," says Dr. Sussex-Pizula.  Still, ephedra without ephedrine alkaloids can be found in some sports supplements, appetite suppressants, and ephedra herbal teas. Chadwick says you should skip it if you're taking any of the following: reserpine, clonidine, methyldopa, reserpine, sympatholytics, MAO inhibitors, phenelzine, guanethidine, and peripheral adrenergic blockers. "There is also an additive effect to caffeine, theophylline, and methylxanthines," she says, meaning it can make the effects stronger. That's why you should "avoid any stimulants if you're prescribed ephedra for a therapeutic reason—and it should only be prescribed by a trained clinician." (P.S. Watch out for ephedra in your pre-workout supplements, too.) Also be mindful of ma huang, a Chinese herbal supplement sometimes consumed in tea form but is derived from ephedra. "[Ma huang is] taken for a number of reasons, including cough, bronchitis, joint pain, weight loss—but a lot of patients don't know that ma huang is an ephedra alkaloid," says Dr. Sussex-Pizula. She advised that ma huang has the same life-threatening side effects as ephedra, and should be avoided.

Vitamin A "should be discontinued while taking tetracycline antibiotics," says Chadwick. Tetracycline antibiotics are sometimes prescribed for acne and skin ailments. When vitamin A is taken in excess, it "can cause increased pressure inside your central nervous system, leading to headaches and neurological symptoms too," says Dr. Sussex-Pizula. Topical vitamin A (known as retinol, and often used to treat skin problems) is generally safe with these antibiotics but should be discussed with your doctor and discontinued immediately if symptoms appear.

CBD is listed as generally safe with no side effects, and can treat anxiety, depression, psychosis, pain, sore muscles, epilepsy and more—but it can interact with blood thinners and chemotherapy, so discuss with a doctor, says Dr. Solomon.

Calcium citrate can treat low blood calcium, but "should not be taken with aluminum- or magnesium-containing antacids and while taking tetracycline antibiotics," says Chadwick.

Dong quai (Angelica sinensis)—also known as "female ginseng," shouldn't be taken with warfarin, says Chadwick. This herb is typically prescribed for menopause symptoms.

Vitamin D is usually prescribed if you have a deficiency (typically from a lack of sun exposure), which can lead to loss of bone density. It can also be used to regulate your immune system and boost mood (some naturopaths use it to mitigate depression). That said, "vitamin D should be monitored if you're on a calcium channel blocker before supplementing large doses," says Chadwick.

Ginger "should not be used in high doses with antiplatelet agents," says Chadwick. "As an additive to food, it is generally safe." Ginger can help aid digestion and mitigate nausea and may support immune function as it is antibacterial. (Here: The Health Benefits of Ginger)

Ginkgo is used naturopathically for memory disorders like Alzheimer's but can thin the blood, thus making it dangerous pre-surgery. "This should be discontinued one week before any surgery," she says.

Licorice "should be avoided if taking furosemide," says Chadwick. (Furosemide is a medication that aids in reducing fluid retention). She also advised skipping licorice if you're taking "potassium-depleting diuretics, digoxin, or cardiac glycosides."

Melatonin should not be used with fluoxetine, (aka Prozac, an SSRI/antidepressant), says Chadwick. Melatonin is often used to help you fall asleep but can inhibit the action of fluoxetine on the enzyme tryptophan-2,3-dioxygenase, reducing the effectiveness of the antidepressant.

Potassium "should not be supplemented if taking potassium-sparing diuretics, as well as other heart medications. Definitely tell your doctor if you are taking potassium," warned Chadwick. This is especially true if you're taking something like spironolactone, a blood pressure medication that is often used to help treat acne and PCOS-related symptoms like excess androgen. Potassium supplements, in this case, could be fatal.

Zinc is used to help shorten the time of your cold or flu, boost your immune system, and can help wounds heal, but it "is contraindicated while taking ciprofloxacin and fluoroquinolone antibiotics," says Chadwick.

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