Do These Herbs Work?

Last Editorial Review: 1/30/2005

Good and Bad Herbs

By Daniel DeNoon
WebMD Feature

Huge sales of herbal remedies say that millions of people believe that they work. What does science say?

A review of every known study of several best-selling herbs appears in the Jan. 1, 2002, issue of the prestigious Annals of Internal Medicine. There are some surprising results.

Edzard Ernst, MD, PhD, of the University of Exeter, U.K., looked at the sciences behind six herbs:

Here's the scoop:

Ginkgo Biloba

The ginkgo tree is one of the oldest types of tree on earth. Traditional Chinese doctors have used its fruits and seeds for thousands of years. They used it mostly to treat asthma and chilblains (the redness, swelling, itching, and burning of the face and extremities caused by exposure to damp cold).

Ginkgo reduces swelling, reduces the supply of oxygen to tissues, scavenges harmful free radicals from the blood, affects metabolism, reduces blood clotting, and improves circulation in tiny blood vessels. In some European countries, it is approved as a treatment for memory impairment, dementia, tinnitus (ringing in the ears), and intermittent claudication (a disease of the arteries that causes pain in the legs when moving but not when at rest).

The findings:

  • Memory Impairment. "Encouraging data exist, but the evidence for ginkgo as a memory enhancer is not fully convincing," Ernst writes. There is no evidence that ginkgo improves brain function in normal people.
  • Dementia. Studies show a small but significant benefit for people with Alzheimer's disease.
  • Tinnitus. A few small studies suggest a moderate benefit, but the jury is still out.
  • Intermittent claudication. Ginkgo works as well as the drug Trental, but regular walking exercises are more effective.
  • Dosage: Most clinical trials used daily doses of 120 mg to 320 mg of a standardized extract of ginkgo leaf. It usually takes four weeks of treatment for effects to be noticed.
  • Safety: Most side effects are mild and soon go away. But the herb can cause possibly serious bleeding and brain seizures if too much is taken. People who are taking blood-thinning medications should NOT take the drug.

St. John's Wort (Hypericum perforatum)

It's been used for many things, but today St. John's wort is considered to be an antidepressant.

The findings:

  • St. John's wort appears to be effective in the treatment of mild-to-moderate depression, Ernst concludes.
  • Dosage: Most trials use about 900 mg of a standardized extract. The effect takes two to three weeks to appear.
  • Safety: Taken all by itself, St. John's wort is quite safe -- much safer than conventional antidepressant drugs. But, this herb has serious interactions with other medicines. These include blood thinners (anticoagulants), oral contraceptives, HIV drugs, and other antidepressant medications (particularly SSRI-type drugs such as Prozac). ALWAYS consult a doctor if taking St. John's wort along with any other drug.

Ginseng (Panax ginseng)

You name it, and ginseng has been used to treat it. Ginseng most commonly is used to improve stamina, concentration, vigilance, and a sense of well-being.

The findings:

  • Energy/physical-performance boosting. Ernst writes that compelling evidence of ginseng for this purpose is lacking.
  • Cancer. A Korean study found that people who took ginseng had significantly lower risk of cancer. By itself, the study proves nothing -- but Ernst calls for more research.
  • Diabetes. One study suggested that the American form of ginseng -- taken with a meal -- lowers the after-meal increase in blood sugar.
  • Dosage: Most studies use 200 mg to 600 mg of extract. Ernst warns against taking more than 1 gram of dry root per day. Low-quality products may be contaminated; be sure to obtain ginseng from reputable sources.
  • Safety: Uncommon -- but severe -- side effects include insomnia, diarrhea, vaginal bleeding, breast pain, severe headache, schizophrenia, and the sometimes-fatal Stevens-Johnson syndrome. Interactions with some drugs have been reported, including the popular blood thinner Coumadin. Contaminated ginseng products may cause some of these adverse effects.


Different echinacea products used different parts of the plant, but most use the roots. This herb contains many potentially active compounds. However, studies find no single active ingredient.

The findings:

  • Upper respiratory tract infections. Results from several studies in people with common colds showed no conclusive results. Some studies suggest that echinacea can prevent colds. "Echinacea ... may be effective, but the trial data are weak and inconclusive," Ernst writes.
  • Dosage: The usual recommended dose is 900 mg to 1,000 mg three times a day. However, some evidence suggests that the most effective preparation is the pressed juice of the Echinacea purpura species. The usual dose is 6 mL to 9 mL. Warning: U.S. echinacea supplements vary widely in quality and often are quite poor, according to Ernst.
  • Safety: Allergic reactions appear to be the most common side effects, but some very serious side effects, including hepatitis and asthma, have been reported. Given the popularity of the herb, Ernst advices a major study of its side effects.

Saw Palmetto

Ripe berries from the dwarf palm have been used to enhance sperm production and to enlarge breast size. The herb today is used to help men with enlarged prostate glands (a condition known as benign prostatic hyperplasia, or BPH).

The findings:

  • Benign prostatic hyperplasia. There's good evidence -- but not absolute proof -- that saw palmetto helps this condition.
  • Dosage: Most clinical studies use a 320 mg extract. Treatment usually lasts for three to six months.
  • Safety: Only rare side effects are reported; these usually are mild. There are no known interactions with other medicines.


A mildly intoxicating beverage used in the South Pacific, kava is mainly used to lessen anxiety but also for insomnia, menopausal symptoms, and other uses.

The findings:

  • "Short-term administration of kava is effective in reducing anxiety," Ernst writes.
  • Dosage: Doses of kava used in most studies range from 70 mg to 240 mg of dried root extract.
  • SAFETY WARNING: A recent FDA alert reported some 25 cases of serious liver damage when people in Germany and Switzerland took kava. Both countries have banned kava products. The FDA issued a warning in March 2002 telling those who use kava supplements or teas to check for possible symptoms of liver damage after similar reports in the U.S. The FDA warns against its use until further studies can be done. The drug also has interactions with alcohol. Long-term users of high-dose kava drinks develop flaky, dry, yellowish skin with hair loss and partial loss of hearing. These symptoms usually go away when people stop taking the herb.

Whether they work well or not, all herbal remedies have effects on your body. Always tell your doctor which herbal remedies you are taking, no matter how safe or effective they may seem.

Originally published Dec. 31, 2001.
Reviewed by Michael W. Smith, MD, May 2002.

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