Meanwhile, 76 percent of adults use dietary supplements. Although most dietary supplement use consists of vitamins and minerals, one-fifth of Americans take medicinal herbs each year. Unfortunately, with greater consumption of all these substances in combination comes a greater risk for interactions. Fortunately, if you take pharmaceuticals, you can take a few steps to ensure safe herb use alongside them.
Herb-Drug Interactions in Perspective
Certainly, we should take herb-drug interactions seriously and do our best to avoid them. However, it helps to gain a little perspective on the fear and hype around herb-drug interactions. Though some serious interactions really do exist, the risk and severity of most herb-drug interactions appears to be relatively low and largely theoretical. On the contrary, with more Americans (particularly elders) taking several pharmaceuticals together, the risk for potentially severe drug-drug interactions is more likely.
Case in point: One study of nearly 500 outpatient veterans found that 43 percent were taking at least one dietary supplement alongside their prescription medications. The researchers analyzed the potential interactions these veterans were exposed to, and found that 45 percent had the potential for a drug-dietary supplement interaction — yet 94 percent of the interactions predicted were not expected to pose a serious danger. This left only 6 percent of the study participants (30 people) at risk of a serious drug-dietary supplement interaction. Meanwhile, drug-drug interactions represent nearly 20 percent of all drug-related adverse effects. The data for death due to dietary supplements is less thorough than that for death due to pharmaceutical drugs, but while more than 100,000 people die annually because of adverse drug effects in general, data from the American Association of Poison Control Centers attributes less than one death per year to the use of herbal and dietary supplements.
Herbs are overall quite safe compared with pharmaceutical drugs, but they can indeed have side effects, and some herb-drug interactions may be severe. Drugs for energy, weight loss, libido, and sports performance have the highest risk of severe side effects and interactions. Here are some steps you can take to safely combine herbal supplements with pharmaceuticals.
Common Herb-Drug Interactions
Some herbs and pharmaceuticals are more prone to interactions than others — and that’s not necessarily a bad thing. Synergistic interactions increase a drug’s activity or effects, while antagonistic interactions decrease them. Herbs may also affect a drug’s clearance from your system (or vice versa). We’re focusing here on how to avoid potentially damaging herb-drug interactions, but many positive herb-drug interactions also exist. For example, combining berberine derived from goldenseal with antibiotics reduces bacteria’s ability to become resistant to the medications; and studies have found that combining curcumin from turmeric with fluoxetine (commonly sold as Prozac) increases the drug’s efficacy in alleviating major depression.
By far, the two greatest areas of potential for real, detrimental herb-drug interactions surround blood-thinning medications (with many herbs) and St. John’s wort (with many drugs).
I’ll also go over a few other herb and pharmaceutical categories known to have potential for undesirable interactions.
St. John’s wort. St. John’s wort (Hypericum perforatum) is the most commonly used herb that poses a high risk for herb-drug interactions, because of two underlying mechanisms. First, it increases the activity of cytochrome P450 enzymes, including CYP3A4. These enzymes — and CYP3A4 in particular — process drugs and toxins in the liver, and their activity affects the length of time a certain quantity of drug will stay in your system. Among the drugs metabolized by CYP pathways are birth control, heart medications, and anti-rejection medications. St. John’s wort tends to clear drugs out of the system too quickly, which could decrease their efficacy. St. John’s wort also decreases serotonin uptake, increasing the amount available in the brain, and thus may increase the risk of serotonin syndrome when combined with other serotonin-boosting substances (primarily antidepressants, but also certain mood, sleep, and pain drugs). The risk here is somewhat theoretical and likely lower than the risk of combining two pharmaceuticals that affect serotonin; however, serotonin syndrome can result in agitation, confusion, rapid heart rate, increased blood pressure, sweating, diarrhea, twitching, and other serious symptoms, and it requires immediate medical attention. In the absence of pharmaceuticals, St. John’s wort tends to be quite safe.
Licorice. Most people don’t think twice about the safety of licorice. It’s in so many teas, candies, and herbal formulas — and yet, safety issues are a concern, especially for those taking large amounts. Licorice can cause hypertension, phytoestrogen and anti-androgen activity, and liver toxicity. It may also interact with various medications, particularly anti-hypertensive and other cardiac drugs. Deglycyrrhizinated licorice (DGL) is generally safe, because glycyrrhizin, the compound responsible for the therapeutic effects, has been removed.
Blood-thinning medications. Coumadin (sold as Warfarin), aspirin, apixaban (sold as Eliquis), and dabigatran (sold as Pradaxa) thin the blood to prevent strokes and other health issues, but they may have life-threatening interactions with herbs, dietary supplements, and foods that increase or decrease clotting time. High or therapeutic doses of ginger, garlic, vitamin E, fish oil, Japanese knotweed, and dong quai, as well as non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, are of particular concern in combination with any blood-thinning medications. Other potentially problematic supplements when paired with blood thinners include evening primrose oil, feverfew, angelica, ginseng, ginkgo, cranberry, red sage, alcohol, blueberry, saw palmetto, green tea, seaweed, turmeric, reishi mushroom, large amounts of leafy greens, vitamin K, and high-salicylate herbs (such as meadowsweet, wintergreen, birch, and willow). This is not an exhaustive list, and there’s limited or conflicting evidence for the effects of some of the items on it. If you take blood thinners, you should carefully research every herb you consider taking to avoid dangerous interactions.
Sedatives. Although sedative interactions are quite likely, they aren’t always as dire as the previous two examples, especially if approached cautiously. Sedative herbs, such as kava, valerian, passionflower, skullcap, chamomile, and lemon balm, may increase sedation when combined with sedative drugs, such as sleep aids, anti-anxiety drugs, some pain medications, and excessive alcohol. In small amounts, the effect of combining sedatives might be desirable: better sleep, or less anxiety. The interaction becomes life-threatening if someone falls asleep while driving or operating heavy machinery, or if their respiration and heart rate drop. If you decide to combine sedative herbs with sedative drugs, do so very carefully, starting with very low herb dosages in a safe setting to assess your personal response.
Fiber, mucilage, and minerals. High-fiber and mucilaginous substances, such as fenugreek, marshmallow root, slippery elm, flax, psyllium powder, and aloe gel, may bind to and slow the absorption of any other substances consumed at the same time. Meanwhile, minerals interact with a handful of medications, including thyroid medications, certain types of antibiotics, osteoporosis medications, digoxin, lithium, and others. It’s unclear if high-mineral herbs, such as nettles and oatstraw, also pose a risk. You can generally take any of these substances safely four hours apart from pharmaceuticals, but double-check with your doctor and pharmacist.
CYP inducers and inhibitors. St. John’s wort is the most well-known herb that affects CYP enzymes, but other herbs may also affect them. CYP inducers can clear medications from the system too quickly, while CYP inhibitors allow drugs to remain longer, potentially increasing their concentration. So far, herbal supplements’ effects on CYP enzymes are the greatest unknown in herb-drug interactions. Besides CYP3A4, herbs may also affect CYP2D6, CYP2C9, and CYP1A2. Interactions may occur with black pepper extract, grapefruit juice, turmeric, green tea, berberine, goldenseal, schisandra, black cumin seed, echinacea, boswellia, and resveratrol. HerbPedia does a nice job presenting various substances and their likelihood for interaction based on current evidence. The Memorial Sloan Kettering Cancer Center and the Natural Medicines Comprehensive Database also cover potential herb-drug CYP interactions. Check with your pharmacist or Mosby’s Nursing Drug Reference to see if your drug is metabolized via CYP pathways before adding herbs to your routine.
As a final note, always be particularly careful when taking medications with a narrow therapeutic window (such as digoxin, a heart medication); to treat extreme illnesses (such as cancer, HIV/AIDS, or liver or kidney failure); or if you’re pregnant or nursing. Use caution with herbs that increase detoxification alongside medications — dosages are calculated based on your body’s normal metabolism, so detoxifying herbs may decrease the efficacy of your medications. While herbs may still be useful, these cases really deserve a qualified herbalist, naturopathic doctor, or holistic doctor to guide you. In general, be aware of your body’s reactions, do your research before you add or remove anything from your medical regimen, and when in doubt, seek out an expert to consult.
How to Introduce Herbs Safely
Truth be told, we can never be absolutely certain that a particular herb won’t interact with a particular drug. The combinations are effectively infinite, and very little data exists to check for potential problems beforehand. That said, herbalists, myself included, report rarely witnessing herb-drug interactions in their clients, especially with a few precautions to limit the likelihood of harmful interactions.
1. Seek guidance. Various health care professionals can help guide you through the herb-drug quagmire. Although you should always keep your doctors informed of any herbs and dietary supplements you’re taking, medical doctors don’t always have the training to assess herb-drug interactions, nor to tell you which herbs you can safely use. Holistic, integrative, and functional medicine doctors, however, may have training in herbal and natural remedies. Pharmacists often have the best access to interaction databases — and are sometimes better trained at using them — so you can always ask your pharmacist to look up a particular herb or dietary supplement and compare it to your current medications. However, if the herb you want to use seems unsafe, your pharmacist probably won’t be able to tell you what to take instead. An herbalist or naturopathic doctor should have the training in both natural healing and herb-drug interactions to be able to offer safe, customized advice based on your needs, and will be able to support you alongside conventional doctors.
2. Do your research. Just as before, keep your doctor and pharmacist informed of the herbs you’re taking; however, if your health concerns are limited and you’re only on one or two medications, you might be able to sleuth out potential herb-drug interactions yourself. Of the resources at your disposal, my favorites include Mosby’s Nursing Drug Reference, which is updated annually and is organized by pharmaceutical drug; and the Botanical Safety Handbook, which is organized by herb. The Natural Medicines Comprehensive Database is also useful, though I find it overly cautious. These resources cost from $45 to $170. You might find copies of Herb, Nutrient, and Drug Interactions by Dwight McKee, Jonathan Treasure, and Mitchell Bebel Stargrove; and The Toxicology of Botanical Medicines by Francis J. Brinker. Both were excellent resources in their time, but are now out of date. Seek more up-to-date information to guide your research. Free online interaction checkers include Aisle7 (also called HealthNotes); Memorial Sloan Kettering Cancer Center; Drugs.com; Mayo Clinic; and A.D.A.M. For easy access to many of these and other sites, check out the science-based herbal resources section of my website, Wintergreen Botanicals.
3. Low dosage. Begin with a low dosage of herbs with the least likelihood of interaction or safety issues, and gradually increase the amount over time to reach the recommended dosage. For example, if you’re planning to take an herbal tincture, try just 1 drop of it the first three days, then move to 5 to 10 drops, then 30 drops — building gradually to the recommended dosage. Pay attention to how you feel, and if you notice any unwanted effects, maintain or reduce the dosage. If appropriate or necessary, ask your doctor to run tests periodically to assess the efficacy and safety of the supplements you’re taking.
Resources to Learn More
- Find an herbalist through the American Herbalists Guild.
- Find a naturopathic doctor through the American Association of Naturopathic Physicians.
- Botanical Safety Handbook
- Natural Medicines Comprehensive Database
- Mosby’s Nursing Drug Reference, sold in bookstores and online.
- Further online resources at Wintergreen Botanicals.
Maria Noël Groves is a registered clinical herbalist nestled in the pine forests of New Hampshire, and the author of the best-selling Body into Balance: An Herbal Guide to Holistic Self-Care and the forthcoming Grow Your Own Herbal Remedies. Visit her website, Wintergreen Botanicals, for herbal recipes and information about her books, long-distance consults, and online classes.