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Evidence Basis for Four Commonly Used Herbs

Am Fam Physician. 2003 Apr 1;67(7):1607-1608.

A substantial portion of patients are using alternative medicines in addition to, or in lieu of, prescription medications. De Smet reviews the regulation, quality, safety, and efficacy of herbal remedies and summarizes the available evidence for four popular herbs: Ginkgo biloba, hawthorn, saw palmetto, and St. John's wort.

Extracts made from the leaves of Ginkgo biloba are commonly used for treatment of dementia, neurosensory problems, and peripheral vascular disease. Active compounds in the extract include ginkgolides, bilobalide, and flavonoids. Part of the interest in the use of ginkgo for vascular conditions stems from ginkgolides' inhibition of platelet-activating factor (PAF). The author notes, however, that most oral preparations may not contain sufficient dosages to produce significant PAF antagonism. One of the better-designed randomized trials that examined the use of ginkgo in patients with dementia showed modest improvement in cognitive function and daily behavior. However, these results were not corroborated by a recent trial comparing twice-daily doses of the same ginkgo extract with placebo. Trials of ginkgo for treatment of claudication also failed to show any consistent, clinically significant benefit. Adverse effects associated with ginkgo include headache, gastric symptoms, allergic skin reactions, and bleeding, especially when the herb is used in combination with other agents that may increase bleeding tendency (e.g., aspirin, warfarin).

Hawthorn extracts are chiefly used for management of mild congestive heart failure. Pharmacologically active compounds in the extracts include oligomeric procyanidins and flavonoids. A review of randomized trials shows some short-term improvement in subjective symptoms and exercise tolerance. Hawthorn has been shown in vitro to have positive inotropic effects on cardiac muscle. The author advocates further study of the effects of long-term use, because several prescription inotropic medications have had deleterious long-term effects in patients with heart failure.

Saw palmetto typically is used for symptomatic treatment of mild to moderate benign prostatic hyperplasia. Studies have shown decreased dihydrotestosterone levels with use of saw palmetto, but unlike the prescription agent finasteride, the herbal compound has not been proved to reduce prostate volume or prostate-specific antigen levels. Several randomized trials have demonstrated saw palmetto's efficacy in reducing urinary symptoms compared with placebo. Adverse effects have been similar to those of placebo.

St. John's wort is widely used for treatment of depressive and anxiety symptoms. Of the several active compounds in the extract, it is unclear which are most important in treatment efficacy. Hypericins previously were thought to be important, but primate studies have revealed no penetration of the blood-brain barrier by these compounds. Recent randomized, controlled trials have not consistently confirmed the positive results of earlier studies of St. John's wort for depression. Adverse effects are less common than those of tricyclic antidepressants.

The author cautions that physicians should not prescribe or recommend herbal remedies without well-established efficacy as if they were medications that had been proved effective by rigorous study.

De Smet PA. Herbal remedies. N Engl J Med. December 19, 2002;347:2046–56.


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