St. John's Wort

Originally Published: August 28, 1998 - Last Updated / Reviewed On: March 9, 2005
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Dear Alice,

What is the most recent information on the beneficial effects of St. John's Wort and possible side effects? What is the recommended dose?


Dear M,

St. John's Wort, known by its botanical name, Hypericum perforatum, is derived from a yellow flowering plant. It's been used for many years, especially in Germany, as an herbal remedy for mild to moderate depression, anxiety, and/or sleep disturbances/disorders. St. John's Wort may also reduce chronic tension headaches.

Research suggests that St. John's Wort raises levels of serotonin, norepinephrine, and dopamine — neurotransmitters that help boost morale and mood.

Unlike prescription anti-depressants (i.e., Prozac, Paxil, Zoloft, Effexor, etc.), which can cause side effects, such as nausea, lowered sex drive, and delayed ejaculation and/or orgasm, St. John's Wort has not been documented as affecting sexual arousal or responses. Side effects that have been reported from using St. John's Wort include:

  • gastrointestinal discomfort, such as upset stomach
  • allergic reactions
  • fatigue
  • restlessness
  • increased sensitivity to sunlight (so, use a sunscreen while taking St. John's Wort)
  • dry mouth
  • confusion
  • dizziness

St. John's Wort is not recommended for the treatment of severe or manic depression, and components of St. John's Wort may raise blood pressure, possibly resulting in a stroke.

Before trying St. John's Wort, or any other natural medicine for that matter, contact your health care provider, because "natural" does not necessarily mean safe. Limited research has been done on women who are pregnant; however, there is some evidence from animal studies that St. John's Wort increases uterine muscle tone, thereby leading to a possible increased risk of premature labor. It has also been suggested that hypericum contains tannic acid, which may interfere with iron absorption. Iron is important for a mother and fetus during pregnancy. Until more is known, women who are pregnant or breastfeeding need to avoid taking St. John's Wort.

Also, don't take St. John's Wort if you are taking any prescription HIV or AIDS medications called protease inhibitors or non-nucleoside reverse transcriptase inhibitors, anti-depressant medications, and/or monoamine oxidase inhibitors (MAOIs) because of possibly dangerous interactions. See the National Center for Complementary and Alternative Medicine of the National Institutes of Health web site for more detailed information.

Since St. John's Wort is a nutritional supplement and as such, not regulated by the U.S. Food and Drug Administration (FDA), the quality of the supplement may vary. In that case, read product labels and look for an extract standardized to 0.3 percent hypericin, the purported active ingredient in St. John's Wort. One source, Herbal Medicine: Expanded Commission E Monographs, a leading publication on herbal medicines, suggests that the ideal dose of St. John's Wort has extracts from the flowering tops of the plant. The dosage of St. John's Wort that has been used in most studies is a 900 milligram daily dose taken in 300 mg increments three times a day. Results may not be seen for at least four to six weeks, if at all. If there are no results after 6 weeks, discontinue its use, since it's probably not effective for you.

At this time, no research has been done to assess St. John's Wort's long-term safety and efficacy. However, the National Institute of Mental Health (NIMH), the National Center for Complementary and Alternative Medicine, and the NIH Office of Dietary Supplements (ODS) conducted the first U.S. large-scale, controlled clinical trial of St. John's Wort in 1998 to assess how effective it is as therapy for clinical depression. The study's findings were published in 2002 in the Journal of the American Medical Association; the conclusion was that St. John's Wort was no more effective for treating moderate depression than a placebo. But the study methodology and the interpretation of the findings by the researchers have been criticized by some in the scientific community as flawed and misleading.

Regardless of the current state of inconsistency in research findings on St. John's Wort's effectiveness, people with mild to moderate depression looking for an alternative to prescription antidepressants may benefit from trying this herbal medicine instead.