Humans, like most mammals, have turned to plants for food and medicine since our earliest times. No doubt some of our ancestors suffered the consequences of unfortunate choices along the way. If you read the book or watched the movie Into the Wild, you realize we sometimes still err, confusing a poisonous plant for edible greenery. People still mistake the death cap mushroom for something more savory. And a couple of years ago, I even found some teenage boys sitting along an irrigation ditch, fashioning poison hemlock stems into cigarette holders.
Nevertheless, most of the medicinal herbs sold in the United States are safe when taken in recommended dosages. More than 38 million Americans use herbs each year, yet the majority of calls to Poison Control Centers about plant ingestions have to do with people (usually children) and pets eating potentially poisonous house and garden plants—not medicinal herbs.
To ensure your experiences with medicinal herbs remain positive—without inadvertent mishaps—follow these nine basic guidelines.
1. Start with Food Herbs
You can bet on safety when you use herbs as foods—think garlic, ginger, nettles, dandelion greens, shiitake mushrooms, nettles, burdock root (also called gobo) and rosehips. Culinary herbs—thyme, oregano, turmeric, cayenne—are also low-risk. Externally applied herbs (compresses, poultices, salves) provide another good testing ground.
The next step is to begin experimenting with infusions (commonly known as “teas”). Many of the food herbs mentioned above can be dried, chopped, and steeped as tea. Extracts of herbs in alcohol (tinctures) or glycerin (glycerites) generally are more potent. Solid extracts, in which all the solvent has been removed, and carbon dioxide-extract herbs are stronger still. Standardized extracts are designed to have a consistent level of suspected active ingredients from batch to batch. This process allows for more precise dosing and easier use in research, but also makes the product closer to a drug.
2. Allergy-Prone? Proceed with Caution
Simon Mills, an internationally known herbal authority and coauthor of The Essential Guide to Herbal Safety (Elsevier, 2005), says, “Allergic reactions are the most common type of herbal side effect although still infrequent.” Sensitive people who handle plants or apply them to their skin could develop contact dermatitis (an itchy skin rash), and inhaling the herbs could aggravate hay fever or asthma. Allergic responses to ingested herbs include skin rash, stomach upset and, at the extreme, life-threatening anaphylaxis.
If you’re allergic to ragweed, you might react to other members of the aster family, such as chamomile, echinacea and feverfew. More rarely, people can have allergic reactions to cayenne, kava (a member of the pepper family), garlic and mints.
“If you are prone to allergic reactions, be careful with your herbal attempts,” Mills says. Try one new herb at a time. Start with half the recommended dose, then gradually increase to the full recommended amount. If you develop a rash, upset stomach, itchy eyes or sneezing, stop taking the herb. If your lips or throat begin to swell, seek emergency care.
3. Investigate Herb-Drug Interactions
If you are taking both herbs and pharmaceutical drugs, you’ll want to avoid two possible scenarios: 1) interfering with the drug’s effects, and 2) amplifying the drug’s effects.
An herb could interfere with a drug’s effects if it acts in the opposite way—for instance, drinking three cups of stimulating black tea or coffee after taking a sedative Valium. An herb also might lower blood levels of a medication, thus thwarting its intended action. St. John’s wort is famous for doing just that. By speeding liver enzyme systems that break down drugs, it reduces blood levels of a long list of medications, including some antihistamines, chemotherapeutic and anti-HIV drugs, warfarin and oral contraceptives.
Furthermore, St. John’s wort, which has a good track record as an antidepressant, shouldn’t be combined with pharmaceutical antidepressants because it can raise blood levels of the chemical serotonin to dangerously high levels.
Combining herbs with drugs that have similar actions can increase the drug’s desired effects or its unpleasant side effects, and the net effect could be good or bad. For instance, some Chinese studies have found astragalus (Astragalus membranaceus) augments some anti-cancer drugs and decreases the drugs’ side effects. (Note: Researchers used injectable forms of the herb.)
In other cases, too much of a good thing can be bad. Taking anticoagulant (“blood-thinner”) drugs (aspirin, warfarin, heparin) with therapeutic doses of anticoagulant herbs (garlic, ginkgo, ginseng and others), for example, can result in bleeding. It’s also wise to discontinue the use of such herbs seven to 10 days before surgery.
As a general rule, avoid mixing herbs and drugs with the same actions so you do not become overly stimulated, sedated, anticoagulated, etc. (For specific combinations to avoid, see read "Avoid These Herb-Drug Combos.")
4. Know When to See Your Health-Care Provider
Sick infants should be seen immediately by a practitioner with pediatric training. Also seek the help of your health-care provider if you know, or suspect, you or another adult has a serious condition. Self-medication with herbs runs the risk of delaying or interfering with medical treatment, potentially with disastrous consequences. Even if you have a mundane illness, make a doctor’s appointment if three days of home care haven’t alleviated your symptoms. Please work in partnership with your physician.
Also, be sure to tell your physician about any herbs you are taking prior to scheduling surgery. Some herbs, especially those with anticoagulant action, should be discontinued seven to 10 days before surgery, or as your doctor advises.
5. Use Extra Caution When Giving Herbs to Children
Babies younger than 6 months (or around the time a child begins eating solid food) should not take herbs internally. Small amounts of gentle herbs can be applied to an infant’s skin via salves, oils, baths and compresses (a cloth dipped in herb tea).
For older children, dosages usually are calculated by weight. Take the child’s weight in pounds, divide it by 150 (an average adult weight) and multiply that number by the adult dose. For instance, if an adult dose is 100 mg and the child weighs 50 pounds, the child’s dose would be 30 mg (50/150 x 100 = 0.3 x 100 = 30 mg).
Children aren’t simply small adults, however. Some herbs generally regarded as safe for adults should not be given to kids. To find out more, ask an herbal expert or get a good book, such as Naturally Healthy Babies & Children by Aviva Romm (Storey Publishing, 2000).
6. Use Gentle Herbs when Pregnant or Nursing
Many plant constituents pass from the intestinal tract into the blood, across the placenta to the fetus’ blood and, later, into breast milk.
If you’re pregnant, you generally should avoid putting anything medicinal into your body. Avoid consuming herbs with laxative effects (senna, cascara sagrada, aloe); hormonal properties (licorice, black cohosh, dong quai, chaste tree, sage, red clover); or stimulant effects (guarana, kola, yerba mate, tea, coffee).
Food herbs usually are safe bets, particularly when used in quantities suitable for flavoring. While no obstetrician will tell you to cease cooking with garlic and oregano, some culinary herbs, such as sage and parsley, might not be recommended in higher therapeutic doses, notes Mills. Most experts agree pregnant women can take these herbs safely: ginger (no more than 1 gram a day to reduce nausea), raspberry leaf, echinacea, chamomile, bilberry (fruit, not leaf), cranberry, hawthorn, hibiscus flowers, rose hips, mullein, spearmint and nettles.
7. Be Wary of Imported Herbs
Some herbal products from Asia, India and the Middle East reportedly have been adulterated with undesirable plants and/or contaminated with heavy metals, sulfites, pesticides and other toxins. In Chinese herbal formulas, herbs can be blended with pharmaceutical drugs not mentioned on the label. Also, Aristolochia fangchi, which has been substituted for other herbs, has been linked to severe kidney damage. Rather than give up on Asian herbs, “I personally would stick to whole herbs I can see, then make my own formulations,” says Mills.
8. Use Essential Oils Wisely
Essential oils are extremely concentrated. Herbalist and aromatherapist Mindy Green gives the following rules for using them safely:
• Don’t apply essential oils to any mucous membrane: mouth, ears, nose, eyes, vagina or rectum.
• Don’t take essential oils by mouth, and keep the bottles out of the reach of small children.
• Don’t apply undiluted essential oils to skin. The standard dilution is 10 to 12 drops of essential oil per one ounce of carrier oil (such as almond or jojoba). Use half that amount or less for people who are debilitated; those with sensitive skin; and for children 5 to 12 years old. Don’t use essential oils for children younger than 5.
• Be cautious when inhaling or applying essential oils to the chest if you are prone to asthma.
9. Educate Yourself.
Anyone interested in herbal medicine should have a good reference book on herb safety.
Try: The Essential Guide to Herb Safety by Simon Mills and Kerry Bone (Elsevier, 2005); Herb Contraindications and Drug Interactions by Francis Brinker, N.D. (Eclectic, 2001); Botanical Safety Handbook by Michael McGuffin, et al (CRC, 1997); and The ABC Clinical Guide to Herbs by Mark Blumenthal, et al (Thieme, 2003).
Avoid these Herb-Drug Combos
As a precaution avoid combining the following herbs and drugs:
Herbs: Kava, California poppy, valerian, skullcap
Drugs: Tranquilizing drugs or alcohol
Herbs: Guarana, yerba mate, coffee, green or black tea
Drugs: Stimulating drugs, such as oral decongestants; asthma drugs, such as albuterol; or pure caffeine
Herbs: Therapeutic doses of American ginseng, Asian ginseng, bitter melon, cinnamon, prickly pear cactus or nopal, ivy gourd and gymnema
Drugs: Drugs that lower blood sugar
Herbs: Ginger, ginseng, garlic and ginkgo
Drugs: Anti-coagulant (blood-thinning) drugs, such as Warfarin
Herbs: St. John’s wort
Drugs: Antidepressants; amitriptyline, cyclosporine, digoxin, fexofenadine, indinavir, methadone, midazolam, nevirapine, phenprocoumon, simvastatin, tacrolimus, theophylline, warfarin, irinotecan; birth control pills
Know these Poisonous Plant Look-Alikes
If you plan to make your own herbal preparations from plants you’ve grown or gathered, be sure the plant is what you think it is. Consult a good basic book on plant identification, such as Peterson Field Guides: Eastern/Central Medicinal Plants and Herbs by Steven Foster and James A. Duke (Houghton Mifflin, 2000) and Western Medicinal Plants and Herbs by Steven Foster and Christopher Hobbs (Houghton Mifflin, 2002).
If you still aren’t sure of the plant’s identity, consult a local botanic garden, horticulture club or university extension program.
• Wild Garlic/Onion (Allium canadense): Edible bulbs and leaves have characteristic onion odor. Used medicinally.
• Death Camas (Zigadenus spp.): Bulb and leaves resemble wild onion; all parts are highly poisonous
• Wild Carrot (Daucus carota): Young root is edible; older roots become woody and tough. Used medicinally.
• Poison Hemlock (Conium maculatum): Leaves resemble wild carrot, but root is highly toxic. Stems have purple markings.
• Comfrey (Symphytum officinale): Leaves sometimes used topically; do not take internally—can cause liver damage.
• Foxglove (Digitalis purpurea): Leaf rosettes that emerge in spring often confused for comfrey with fatal results.
Herbs and Liver Damage
Herb expert James Duke, Ph.D., points out that many more herbs protect the liver than harm it. In fact, one of America’s favorite over-the-counter drugs, acetaminophen (Tylenol and other brands), is riskier than most herbs. Although safe within recommended dosages, acetaminophen overdoses (some of which occur among people simply trying to relieve their pain) are the main cause of acute liver failure, and contribute to 500 American deaths a year.
That said, the following herbs should be avoided, particularly in people with known liver disease, heavy drinkers (or users of recreational drugs), and those taking liver-taxing drugs, such as acetaminophen (Tylenol), aspirin, nonsteroidal anti-inflammatories (such as ibuprofen), corticosteroids, statins, tetracyclines and others).
Herbs that contain pyrrolizidine alkaloids: comfrey, coltsfoot, senecio, borage leaf and germander. Comfrey has gotten the most media attention for its connection to liver injury. In 2001, the Food and Drug Administration advised manufacturers to remove from the market comfrey products intended for internal use. Because this herb is a good wound healer, it’s often an ingredient in first-aid salves. Another PA-containing herb, butterbur, is available as a PA-free extract (Petadolex) for the prevention of migraine headaches and hay fever.
Kava (Piper methysticum). For many years, people of the South Pacific have consumed kava beverages with the single side effect of a scaly, yellowish skin condition with excessive use. Research showing concentrated kava extracts reduced anxiety spurred its widespread popularity. Although human studies didn’t register liver toxicity, cases of liver injury (some severe) cropped up several years ago. Most involved ingestion of kava extracts made with acetone or alcohol, and often along with alcohol or drugs that can be hard on the liver.
Mark Blumenthal, founder and executive director of the American Botanical Council, says, “no convincing proof of an inherent toxicity of kava exists,” despite ongoing research. And, while he believes kava to be relatively safe, “the jury is still out as to whether kava might cause liver injury, particularly in susceptible individuals.”
Steven Dentali, Ph.D., Chief Science Officer for the American Herbal Products Association, adds, “Considering the widespread consumption of kava beverage and the long history of apparent safe use, any toxic liver reactions are of course serious, but extremely rare.”
A general guideline: Don’t take herbs that have even a suspicion of harming the liver if you already have liver disease or regularly drink alcohol or use recreational drugs. Also avoid these herbs if you take a medication that can be toxic to the liver. Consult your health-care provider if you are unsure.
Linda B. White, M.D. is the coauthor of The Herbal Drugstore. An assistant professor, White teaches classes in herbal medicine in the Program in Integrative Therapeutic Practices at Metropolitan State College of Denver.