When Herbs Bite Back

Roughly half of all U.S. drugs are synthetic versions of plant-derived chemicals or modifications of those natural compounds. It should come as little surprise, therefore, that many botanical preparations–either fresh from the garden or boxed from your local supermarket–prove biologically active. Indeed, it’s with this expectation that many people grow or buy what have come to be known as medicinal plants.

Foxglove (Digitalis purpurea) made it onto Amy Christine Brown’s harmful herb list as a heart poison. Its active ingredient is a stimulant originally used to treat patients with congestive heart failure. John Snyder
All parts of jimsonweed (Datura stramonium) are toxic. Agriculturally renowned as one of the world’s worst weeds and prescribed by natural healers of the past to treat asthma, cough, bronchitis, and epilepsy, this herbal remedy can elicit a host of symptoms, including hallucinations–and even kill. University of Illinois at Springfield

However, toxicologists are quick to point out, dose makes the poison.

While a cup of herbal tea may soothe an upset tummy, regularly downing a quart of the brew might actually provoke disease.

With such concerns in mind, Amy Christine Brown of the University of Hawaii identified scientific reports of adverse events linked to consumption of herbal products. She used MEDLINE, the National Library of Medicine’s database of references to more than 11 million articles. These abstracted reports have been culled from some 4,300 biomedical-research journals.

Brown focused on multiple reports indicating that a botanical product had been linked to one of five conditions: liver, kidney, or heart damage, cancer, or death. She acknowledges that allergies and contact dermatitis–rashes such as those caused by poison ivy–can provoke severe discomfort, but in her work, she ignored them in favor of more serious reactions. However, once she identified a product linked to one of the five selected conditions, she noted other symptoms described in the reports.

Brown bypassed accounts of adverse interactions between herbals and conventional drugs–in part, because partitioning the roles of the herb, the drug, and the consumer’s disease was daunting.

She presented preliminary tables of her data on April 22 in New Orleans at the Experimental Biology 2002 meeting.

These tables form the basis of what she expects to be a growing, harmful-herb list. Brown plans soon to post her accumulating tally on the Internet. The nutrition researcher wants the list to forewarn consumers, physicians, and companies marketing herbal products about the potentially dangerous alter ego of some natural nutraceuticals–foods and other natural products with druglike properties.

From licorice to sassafras

None of the plants that made her list would qualify as dietary staples. In fact, most are uncommon in Western households.

Consider jin bu huan (Lycopodium serratum), a traditional Chinese analgesic and sedative. It contains levo-tetrahydropolmatine, a potent neuroractive substance. Heavy use of this medicinal has caused life-threatening respiratory distress, abnormally slow heartbeats, and liver damage. Mu tong or chocolate vine (Aristolochia manshuriensis)–an Asian cure for conditions including swelling, urinary tract infections, diabetes, and poor circulation–has been linked to acute kidney failure. Then, there’s celandine (Chelidonium majus), a plant that’s been used topically to treat warts and eczema and internally to cope with indigestion and gallstones. Reports have traced at least 10 cases of hepatitis to this herbal remedy, whose suspected toxicants are isoquinoline alkaloids.

A few herbs that made the list sound benign. One example is licorice (Glycyrrhiza glabra), a traditional treatment for ulcers, cough, and inflammation. Unfortunately, its triterpene saponins and hydroxycoumarins are among the agents reported to have triggered several cases of high blood pressure, an abnormal drop in the blood’s potassium concentration, an abnormal elevation in the blood’s sodium concentration, heart failure, and death.

Lily of the Valley (Convallaria majalis) possesses powerful cardiac glycosides similar to those potentially deadly compounds produced by foxglove (Digitalis purpurea). A few people who medicated themselves with Lily of the Valley to treat heart disease, poor circulation, and swelling ended up with nausea, vomiting, dangerously irregular heart beats, and even cardiac shock.

Then, there’s sassafras (Sassafras albidum), the flavoring agent in old-fashioned root beer. In the past, traditional healers have prescribed it for urinary tract problems, mucus membrane inflammation, rheumatism, and syphilis. Though Brown says it-s still available as an herbal tea, her MEDLINE search shows that this plant has triggered muscle coordination problems, drooping of the upper eyelids, hypothermia and, at least in animals, cancer.

Also on her harmful-herb list are comfrey (Symphytum officinale), coltsfoot (Tussilago farfara), and groundsel (Senecio vulgaris)–a trio of herb garden regulars with a host of alleged medicinal properties. All, however, contain pyrrolizidine alkaloids, chemicals that the liver converts into potentially deadly poisons (see Honey of a Threat: Honey of a Threat).

The list’s novelty

In Germany, where physicians can and often do prescribe herbal medicines, the government commissioned a series of monographs, known as the German Commission E (GCE). Each report describes the known medicinal properties–and toxicity–associated with an individual herb.

To date, however, GCE doesn’t include a master list of botanical products with potentially harmful attributes, Brown notes. Nor, she adds, is such a list available from the U.S. Food and Drug Administration, Centers for Disease Control and Prevention, or Department of Agriculture.

She says that her new list offers, for the first time, one-stop shopping for people interested in identifying major herbal risks. As such, she suspects it could serve as a follow-up to FDA’s Dietary Supplement Health and Education Act, which identifies herbal products warranting regulation. Her list would highlight “herbs that need to be treated with caution.”

Indeed, she notes, some people equate natural products, such as herbal remedies, with safety. She hopes her list will drive home the fallacy in such logic.

However, she resists the idea that her list might serve as the blueprint for a campaign to ban common herbs. She contends, “You can’t apply a sledgehammer to [regulate] herbs when you’re not even applying a hammer to pharmaceutical drugs.” Her review of the herbal literature suggests that perhaps only 0.2 percent of their use has resulted in adverse reactions, compared to 4.4 percent of pharmaceutical drug use. Indeed, Brown points out, the reports she unearthed in her MEDLINE search usually identify only sporadic poisonings. Most of those reports failed to identify a mechanism of action, whether the victims had some underlying genetic or medical susceptibility to toxicity, or even whether the toxicity necessarily traced to a single agent–as opposed to, for example, some interaction with other items in the diet.

While she’d like her data to forewarn users of the power of botanicals, she hopes it won’t cause them to ignore their potential value. Indeed, she explains, “I’m basically pro-herb.”

Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

From the Nature Index

Paid Content