What Is St. John's Wort?

Medically Reviewed

St. John’s wort (Hypericum perforatum) is a yellow flowering weed that has been used to treat various “nervous disorders” for centuries. It is sold in Germany, usually by prescription, as an antidepressant and in the United States as a dietary supplement. This herb contains at least seven groups of compounds that can have pharmacological action.

Claims, purported benefits: Alleviates depression, anxiety, sleep disorders, irritable bowel syndrome, hot flashes, and premenstrual syndrome (PMS). Helps with smoking cessation.

What the science says: St. John’s wort is one of the most researched herbal medicines, in particular for its use in depression. But results have often been inconsistent and hard to compare, largely because the studies have included people with different types and degrees of depression, used different herb preparations and doses, tested the herb against low doses of antidepressants, and/or did not have placebo groups.

Still, most studies have been favorable, and the consensus is that St. John’s wort works better than a placebo in treating people with mild to moderate depression, at least in the short term. It also seems to be as good as older-generation tricyclic antidepressants and, possibly, newer antidepressants for people with this level of depression, with fewer serious side effects.

The Natural Standard, which evaluates complementary and alternative therapies, has deemed the evidence convincing for St. John’s wort as a treatment for mild to moderate depression. St. John’s wort may raise levels of mood-enhancing chemicals in the brain (serotonin, dopamine, and norepinephrine), which is similar to the way SSRI antidepressants work. Which constituents in the plant’s leaves and flowers may be responsible for its antidepressant action is not clear.

A well-designed study in Menopause in 2010 found that St. John’s wort decreased hot flashes after eight weeks, but some other studies have shown no such benefit from the herb.

What it doesn’t help: Studies do not support the use of St. John’s wort for severe depression, depression of long duration, or bipolar disorder. There’s little or no good evidence that it relieves anxiety, obsessive-compulsive disorder, seasonal affective or sleep disorders, or premenstrual syndrome. It may also not help with minor depression. For instance, a well-designed 2011 study in the Journal of Psychiatric Research found that St. John’s wort worked no better than a placebo in people with minor depression over a 12-week period, but had more adverse effects.

People with irritable bowel syndrome (IBS) are often prescribed antidepressants, but they sometimes turn to alternative medicine instead, including St. John’s wort. In 2010, however, a well-designed study from the Mayo Clinic found that St. John’s wort worked no better than a placebo in relieving IBS symptoms.

The long-term safety and effectiveness of St. John’s wort are not known. Most studies have lasted less than three months. Moreover, it is not clear what the best dosage is. Although 900 milligrams a day (standardized to contain 0.3 percent hypericin and split in three doses) is commonly recommended, studies have used a range of preparations and dosages. St. John’s wort supplements vary in preparation and quality, and they may not all have the same effects as those used in studies.

Common side effects: St. John’s wort is generally well tolerated, but mild side effects include gastrointestinal upset, headaches, fatigue, and dry mouth. However, an Australian study in 2015 found that the herb can produce the same side effects as prescription anti- depressants, and that serious side effects can occur when the two are combined.

Most important, it can interfere with many drugs, including statins, the blood thinner warfarin, certain HIV medications, digoxin (a heart drug), and oral contraceptives. Because of these potentially dangerous interactions, in 2013 a pharmacists’ group asked the FDA to restrict sale of the supplement to behind the pharmacy counter. In 2014, a study in the Journal of Alternative and Complementary Medicine analyzed a large national medical database and found that among people who reported using St. John’s wort, 28 percent were also taking medication that’s unsafe to combine with it.

St. John’s wort should be used cautiously, if at all, in people with bipolar or other psychiatric conditions. It may interact with other antidepressants and psychoactive medications. Pregnant and nursing women should not take St. John’s wort.

Our advice: Depression is a serious condition, and you should not self-diagnose or self-medicate. While there is continuing debate about how effective prescription antidepressants really are, beyond their powerful placebo effect, these drugs are still often a first-choice treat- ment, especially for more severe depression. St. John’s wort may be an option for mild to moderate depression, but keep in mind that research on it has produced mixed results and that there is considerable variation in commercially available supplements. If you are already taking a prescription antidepressant, don’t switch to St. John’s wort on your own, and don’t combine the two.