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St. John's Wort

Other common name(s): goatweed, amber, klamath weed, tipton weed

Scientific/medical name(s): Hypericum perforatum


St. John's wort is a shrub-like perennial herb with bright yellow flowers that is native to Europe, western Asia, and northern Africa. Colonists brought it to the United States, where it now grows widely. The parts of the plant used in herbal remedies are taken from the flowering tops.


St. John's wort has been shown to be effective in treating mild to moderate depression and causes fewer side effects than older types of antidepressants (tricyclics or TCAs). Data suggest it may be less effective in treating severe depression. More research is needed to compare it to newer antidepressants.

St. John's wort is known to interfere with many prescription drugs, including some used for anesthesia and cancer treatment.

How is it promoted for use?

St. John's wort is widely used in Europe to treat depression, anxiety, and sleep disorders. In Germany, doctors prescribe it more often than the popular anti-depressant drug Prozac. Hypericin is the most commonly studied active ingredient in St. John's wort, and the amount of this compound is often used to standardize extracts.

The herb is also promoted to treat bronchial inflammation, bed-wetting, stomach problems, hemorrhoids, hypothyroidism, insomnia, migraines, kidney disorders, and malaria. A balm made from St. John’s wort can be used on the skin for burns, wounds, insect bites and stings, and other skin diseases. Although there is some evidence for using St. John's wort in some emotional conditions besides depression, available scientific evidence does not support claims that it works for these other diseases.

What does it involve?

Commission E (Germany's regulatory agency for herbs) has approved St. John's wort for the treatment of depression and anxiety, as well as for burns and skin lesions. It is available by prescription only in Germany. However, it can be purchased in drug stores and health food stores in the United States as a capsule, tablet, liquid extract, and as a tea. An average dose is 300 milligrams, taken 3 times a day for 4 to 6 weeks.

Unfortunately, the potency and purity of different extracts sold in the United States varies widely. The US Food and Drug Administration does not regulate herbs as tightly as it does prescription and over-the-counter medicines and cannot guarantee strength or purity.

A 2003 study using a new type of test found that most brands of St. John's wort contained a different amount of hypericin (or psuedohypericin), one of the active ingredients in St. John’s wort, from what was listed on the label. ranging from 0% to 109% of what was listed for capsules, and 31% to 80% of what was listed for tablets. On average, the labels stated that the product contained about twice as much hypericin and pseudohypericin as it actually contained. Some products contained no detectable St. John’s wort, and others contained less than a third of what the label stated. Very few contained the stated amount. This variability can affect the results people might get when they try to follow a standard dose. Standardized products are supposed to contain 0.3% hypericin. The variability in strength may also affect the outcomes of research on the herb, unless researchers confirm the contents of the brand before testing it.

What is the history behind it?

Use of St. John's wort dates back many centuries and is surrounded with folklore. Greeks used it to fight fevers and evil spirits. Its scientific name comes from the Greek words hyper (meaning over) and eikon (meaning ghost). In pre-Christian rituals in England, the plant was used to protect a house from evil spirits and to banish witches. It was thought that a person could be protected from death during the following year by putting a piece of the plant under a pillow on St. John's Eve, after which the Saint would appear in a dream and give his blessing. The plant's common name reflects the fact that the flowers typically bloom around the birthday of St. John the Baptist, June 24.

St. John's wort has been used as a folk remedy for centuries to treat everything from wounds, headaches, gout, and kidney problems to nervous disorders. After it was brought to this continent, Native Americans used several species of St. John’s wort to treat diarrhea, wounds, and snakebites.

In the United States, the plant was not well known until after the 1900s. In 1959, the plant was first studied for its ability to fight bacteria. Extracts of St. John's wort have become extremely popular in the United States. Since its interactions with other drugs have been discovered, there are more concerns about its potential dangers. Ireland, for instance, banned over-the-counter sales of the herb in 2000. It is still available by prescription there.

What is the evidence?

Clinical trials have shown that St. John’s wort is effective in treating mild to moderate depression and causes fewer side effects than older standard antidepressants (tricyclics or TCAs).

Researchers are uncertain about how St. John's wort works to relieve depression. Hypericin was first recognized as its active ingredient, but newer information indicates that hyperforin, another compound in the herb, also plays an important role.

One review that analyzed 23 randomized clinical trials concluded that St. John’s wort was more effective than a placebo, or inactive substance, for the treatment of mild to moderate depression and was found to be as effective as standard antidepressants. A more recent review of controlled, double-blinded studies reached a similar conclusion. However, the review authors reported that there were problems with the way the studies were designed and analyzed.

In 2004, a German group analyzed 30 studies that looked at St. John’s wort for mild to moderate depression and found that the herb compared well to newer antidepressants. In the studies looking at mild depression, patients taking St. John’s wort sometimes had better results than with standard treatment.

Studies are mixed with regard to its effectiveness in treating severe depression, but recent clinical trials suggest that it does not work as well. The US National Institutes of Health—in cooperation with the Office of Alternative Medicine, the National Institute of Mental Health, and the Office of Dietary Supplements—launched a double-blind, controlled clinical trial using St. John's wort in the treatment of patients with major depression. A total of 340 adult patients were followed over a period of 2 to 6 months. The study compared the effects of St. John’s wort, a placebo, and a newer antidepressant called sertraline. The study showed that neither the St. John’s wort nor the sertraline was more effective than the placebo. This and similar studies suggest that St. John’s wort may not be effective for moderate to severe depression, although this study was criticized because the approved antidepressant also showed no benefit.

St. John’s wort has also been studied as a treatment for attention-deficit/hyperactivity disorder. A recent clinical trial for this condition found St. John’s wort to be no different from placebo.

New studies are looking more closely at the interaction of St. John’s wort with birth control pills and strong pain medicines called opioids. St. John’s wort is also being studied to find out whether it helps in the treatment of minor depression, social phobia, and obsessive-compulsive disorder.

One non-randomized clinical trial suggested that St. John’s wort may have potential in helping people to stop smoking. This is an interesting idea, as other antidepressants have been useful in smoking cessation. However, additional study is needed before St. John’s wort can be considered to be effective in this situation.

A few laboratory studies are testing some substances from St. John’s wort as a cancer treatment. However, this research is quite preliminary, and no clinical studies have been reported.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike companies that produce drugs (which must provide the FDA with results of detailed testing showing their product is safe and effective before the drug is approved for sale), the companies that make supplements do not have to show evidence of safety or health benefits to the FDA before selling their products. Supplement products without any reliable scientific evidence of health benefits may still be sold as long as the companies selling them do not claim the supplements can prevent, treat, or cure any specific disease. Some such products may not contain the amount of the herb or substance that is written on the label, and some may include other substances (contaminants). Though the FDA has written new rules to improve the quality of manufacturing processes for dietary supplements and the accurate listing of supplement ingredients, these rules do not take full effect until 2010. And, the new rules do not address the safety of supplement ingredients or their effects on health when proper manufacturing techniques are used.
Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

Side effects are not common but include upset stomach, constipation, fatigue, dry mouth, dizziness, headache, drowsiness, sleep disturbances, skin rash, and extreme sensitivity to sunlight. People taking St. John’s wort should use sunscreen and eye protection when exposed to sunlight and should avoid tanning beds. It can also lower the sex drive. Allergic reactions are rare, but rashes have been reported. Information on the long-term effects or usage of St. John's wort is not currently known. In some patients, when the herb has been taken for more than a month, stopping it suddenly can cause withdrawal symptoms such as nausea, vomiting, dizziness, dry mouth, and extreme fatigue.

St. John's wort interferes with several important medicines, such as HIV drugs (antiretrovirals), blood thinners, birth control pills, and heart medicines such as digoxin. The herb can reduce the effectiveness of some anticancer drugs such as irinotecan and imatinib. It may also interact with drugs such as cyclosporine that keep the body from rejecting transplanted organs. St. John’s wort may increase sleepiness if used with alcohol, narcotics, sedatives, sleeping medicines, and anticonvulsants (drugs to prevent seizures). Other medicines that may interact badly with St. John’s wort include an antidiarrhea medicine called loperamide, an asthma medicine called theophylline, and some blood pressure medicines.

St. John’s wort should not be used with other antidepressants because it could cause serotonin syndrome. This is a potentially fatal complication of the brain chemistry involving confusion, fever, hallucinations, poor coordination, nausea, vomiting, shakiness, restlessness, sweating, and other symptoms caused by an increase in serotonin activity.

People taking any prescription medicines or other herbs should talk to their doctors or pharmacists about possible interactions before taking St. John's wort. Because of its potential to interfere with anesthetics, it should be discontinued at least a week before surgery.

People with severe depression or manic depression (bipolar disorder) should not use St. John's wort. The herb may also increase muscle contractions of the uterus and is known to pass into breast milk. It should not be used by pregnant or breast-feeding women. Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

Additional resources

More information from your American Cancer Society

The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345).

Dietary Supplements: What Is Safe?

The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management

Complementary and Alternative Methods and Cancer

Placebo Effect

Learning About New Ways to Treat Cancer

Learning About New Ways to Prevent Cancer


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Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.

Last Medical Review: 11/28/2008
Last Revised: 11/28/2008