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Clinical Reviews

How to judge an herbal remedy

How do you determine usefulness? It’s a matter of efficacy, safety, quality, and cost.

January 2005 · Vol. 17, No. 1
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How many of your patients take herbal preparations? More than you think, thanks to the proliferation of products. Between 1990 and 1997, the US population increased its use of herbal medicines by 380%, and total out-of-pocket expenditures in 1997 were $5.1 billion (TABLE 1).1,2

Safety issues surrounding herbal medicine are complex: possible toxicity of herbal constituents, presence of contaminants or adulterants, and potential interactions between herbs and prescription drugs. In addition, the preparations are often poor in quality. One reason: They are inadequately regulated, a problem many experts hope to change. Cost evaluations of herbal medicines are not available.

This article offers guidelines for prescribing herbal medications, as well as advice on when they are unwise.


10 best-selling herbal medicines





Ginkgo biloba















Saw palmetto



St John’s wort









Black cohosh


* US, 2001 data

Is the herb effective for the patient’s condition?

Although data are incomplete, some treatments have shown promise (TABLE 2), and findings indicate serious adverse effects of certain treatments (TABLE 3).

Besides safety, the critical question is: Does the remedy work for the patient’s condition? Do not prescribe or recommend an herbal remedy if the answer is not a firm yes.

Herbal medicines usually contain a range of pharmacologically active compounds. In some cases, it is unclear which constituents produce the therapeutic effect. Testing for efficacy in this situation is obviously more complex than with synthetic drugs. One approach is to view the entire herbal extract as the active component.

To optimize the reproducibility of efficacy studies, extracts must be sufficiently characterized. This is often achieved by standardizing the amount of a single key constituent (eg, a pharmacologically active ingredient or a marker suitable substance if such an ingredient is unknown).

Once the dilemma of standardization is solved, herbal medicines are scrutinized in much the same way as other drugs. The literature contains several randomized, clinical trials and systematic reviews/meta-analyses of these studies.3,4 The Cochrane database includes about 30 systematic reviews of herbal medicines, and several authoritative books recently were published.3-6

Unfortunately, systematic reviews are often limited by the paucity and varied methodological quality of the primary studies,3,7 and research funds are generally scarce, in part because plants cannot be patented.

Generalizations about the efficacy of herbal medicines are not possible. Each remedy must be judged on its own merits. Some herbal products have demon strated efficacy for certain conditions, while others have not. Overall, few products have been subjected to extensive clinical testing.3

The bottom line? As a review in the New England Journal of Medicine concluded, “Clinicians should not prescribe or recommend herbal remedies without well-established efficacy.”7

Tradition is no guarantee, as in the case of kava

Consumers are attracted to herbal medicines in part because they equate “natural” with “safe.” Yet some herbal medicines pose serious risks.7

First, the active ingredients in herbal preparations can cause both desirable and undesirable effects. TABLE 3 lists examples of commonly used herbal medicines that have been associated with serious adverse effects.3 Traditional use is no guarantee of safety and no acceptable substitute for data.8

A poignant example is kava (Piper methysticum), an herbal remedy that has been used for centuries, apparently without problems. Numerous rigorous clinical trials have shown it to be a powerful anxiolytic agent,9 but it was recently associated with several cases of serious liver damage.10 As a result, it was withdrawn from the markets of several European countries, and the US Food and Drug Administration (FDA) has issued warnings about its hepatotoxic potential.

Second, the active ingredients in herbal medicines can interact with prescription drugs. For instance, extracts of St. John’s wort (Hypericum perforatum) act as an enzyme inducer on the cytochrome P450 system and increase the activity of the P-glycoprotein transmembrane transporter mechanism. Both effects lead to a reduction of the plasma level of several conventional drugs.11 Perhaps the most serious consequence would be insufficiently low cyclosporine levels in patients after organ transplantation, which jeopardize the success of this procedure.12

Third, some herbal medicines (particularly Asian herbal mixtures) are contaminated with heavy metals13; contain misidentified, toxic herbal ingredients14; or are adulterated with prescription drugs.15 Be sure an herbal medication cannot cause harm before prescribing or recommending it.


7 herbal medicines associated with serious adverse effects*




Aloe vera (Aloe barbadensis)


Juice may cause intestinal pain and electrolyte loss

Feverfew (Tanacetum parthenium)

Migraine prevention

“Post-fever syndrome” after discontinuation (migraine, anxiety, insomnia, muscle stiffness)

Hawthorn (Crataegus)

Congestive heart failure

Additive effects with other cardiac glycosides

Kava (Piper methysticum)


Toxic liver damage

St. John’s wort (Hypericum perforatum)


Increased clearance of a range of prescribed drugs

Tea tree oil (Malaleuca alternifolia)

Skin problems (external)

Allergic reactions

Valerian (Valeriana officinalis)


Morning hangover

* This is a sampling only. Also, without positive safety data, herbal medications cannot be considered safe for pregnant or nursing women.

Uneven quality marks herbal medicines

The quality of an herbal preparation contributes to its efficacy and safety. Herbal dietary supplements usually are unregulated as drugs and can vary widely in quality—to the point of being ineffective.7,16

In the United States, herbal preparations must meet the requirements set forth in the Dietary Supplement and Health Education Act (DSHEA) of 1994. Thus, they are marketed without FDA approval of their efficacy and safety. The DSHEA prohibits companies from making medical claims for dietary supplements, but does allow structure or functional claims. If safety concerns arise, the burden of proof lies not with the manufacturer, but with the FDA.

Many experts believe this regulation is insufficient to guarantee consumer safety and argue for it to be changed.16 In Europe, new legislation will soon require efficacy to be based on bibliographic data, and safety will be governed as it is with conventional drugs.17

Not enough data to base decisions on cost

As a general rule, clinicians should try to recommend treatments that save money for patients and the health-care system. Although herbal medications are relatively inexpensive, few proper economic analyses exist.18,19 So far, only 1 cost evaluation20 of an herbal medicine has been published. This study involved treatment of symptomatic chronic venous insufficiency and compared the cost-effectiveness of compression stockings with that of an extract of horse chestnut seeds; the treatments were comparable.

For the prescribing physician, this means decisions cannot be based on conclusive cost-analyses. Until such studies are available, decisions must be informed by our knowledge of the efficacy, safety, and quality of herbal medications.

Herbal hazards: Heavy metals and undeclared ingredients

One of 5 Ayurvedic herbal medicine products may contain potentially toxic levels of lead, mercury, and/or arsenic, according to a study in the December 15 issue of JAMA. The Ayurvedic tradition is a holistic healing system that originated in India. When researchers tested Ayurvedic products produced in South Asia and sold in the Boston area, 14 of 70 contained heavy metals. If taken according to the package directions, the preparations would exceed published standards for the metals, some of them by a huge margin.

Pharmaceuticals in an herbal remedy?

Among other hazards detected in herbal products are undeclared prescription drugs mixed into the ingredients of some Chinese preparations, according to the FDA. And last May, Consumer Reports identified 12 dietary supplements “too dangerous to be on the market,” yet all were readily available in stores or online. They include comfrey, androstenedione, chaparral, and kava.

Pose the question

All the more reason to ask patients what products they may be using. Ask specifically about herbal or natural remedies, since many people do not consider them drugs and fail to disclose them to physicians.

—The editors

This article was adapted from: Ernst E. Prescribing herbal medications appropriately. J Fam Pract. 2004;53:958–988.


1. Eisenberg DM, David RB, Ettner SL, et al. Trends in alternative medicine use in the United States. JAMA. 1998;280:1569-1575.

2. Blumenthal M. Herb sales down in mainstream market, up in natural food stores. Herbal Gram. 2002;55:60.-

3. Ernst E, Pittler MH, Stevinson C, White AR. The Desktop Guide to Complementary and Alternative Medicine. Edinburgh: Mosby; 2001.

4. Fugh-Berman A. The 5-minute herb & dietary supplement consult. Philadelphia: Lippincott Williams & Wilkins; 2003.

5. Capasso F, Gaginella TS, Grandolini G, Izzo AA. Phytotherapy: A Quick Reference to Herbal Medicine. Berlin: Springer-Verlag; 2003.

6. Schulz V, Hänsel R, Tyler VE. Rational Phytotherapy. Berlin: Springer-Verlag; 2001.

7. De Smet PAGM. Herbal remedies. N Engl J Med. 2002;347:2046-2056.

8. Ernst E, De Smet PAGM, Shaw D, Murray V. Traditional remedies and the “test of time.” Eur J Clin Pharmacol. 1998;54:99-100.

9. Pittler MH, Ernst E. Kava extract for treating anxiety. Cochrane Library 2002.

10. Teschke R, Gaus W, Loew D. Kava extracts: safety and risks including rare hepatotoxicity. Phytomed. 2003;10:440-446.

11. Carlo GD, Borrelli F, Ernst E, Izzo AA. St. John’s wort: Prozac from the plant kingdom. TRENDS in Pharmacol Sci. 2001;22:292-297.

12. Ernst E. St John’s wort supplements endanger the success of organ transplantation. Arch Surg. 2002;137:316-319.

13. Ernst E, Thompson Coon J. Heavy metals in traditional Chinese medicines: a systematic review. Clin Pharmacol Ther. 2001;70:497-504.

14. Nortier JL, Martinez MC. Urothelial carcinoma associated with the use of a Chinese herb (Aristolochia fangchi). N Engl J Med. 2000;342:1686-1692.

15. Ernst E. Adulteration of Chinese herbal medicines with synthetic drugs: a systematic review. J Int Med. 2002;251:107-113.

16. De Angelis CD, Fontanarosa PB. Drugs alias dietary supplements. JAMA. 2003;290:1519-1520.

17. Silano M, De Vincenzi M, De Vincenzi A, Silano V. The new European legislation on traditional herbal medicines: main features and perspectives. Fitoterapia. 2004;75:107-116.

18. Kernick D, White A. Applying economic evaluation to complementary and alternative medicine. In: Kernick DE, ed. Getting Health Economics into Practice. Oxford: Radcliffe Medical Press; 2002;173-180.

19. De Smet PAGM, Bonsel G, Van der Kuy A, et al. Introduction to the pharmacoeconomics of herbal medicines. Pharmacoeconomics. 2000;18:1-7.

20. Rychlik R, Marshall M, Bachinger A, et al. Ökonomische Aspekte der Therapie der chronisch venösen Insuffizienz. Gesundh ökon Qual Manag. 1997;2:86-91.

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