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St. John's Wort

Medically reviewed on Jul 23, 2018

What is St. John's Wort?

St. John's wort is a perennial plant native to Europe, but now found throughout the US and parts of Canada. The plant is an aggressive weed found in the dry ground of roadsides, meadows, woods, and hedges. It generally reaches a height of 0.3 to 0.61 m, except on the Pacific coast of the US where it has attained heights of 1.5 m. The plant has oval-shaped leaves and yields golden-yellow flowers. The petals contain black or yellow glandular dots and lines. There are about 370 species in the genus Hypericum, which is derived from the Greek words, hyper and eikon meaning "over an apparition," alluding to the plant's ancient use to ward off evil spirits. Perforatum refers to the leaf's appearance. When held up to light, the translucent leaf glands resemble perforations. Harvest of the plant for medicinal purposes must occur in July and August; the plant must be dried immediately to avoid loss of potency. The dried herb consists of the plant's flowering tops.

Scientific Name(s)

Hypericum perforatum L. Family: Hypericaceae

Common Name(s)

St. John's wort also is known as klamath weed, John's wort, amber touch-and-heal, goatweed, rosin rose, and millepertuis. Commercial preparations used in trials include Esbericum, Hyperforat, Hyperiforce, Kira, LI 160, Neuroplant, Psychotonin, Sedariston, STEI 300, WS 5573, Ze 117.

Trade Names

  • Esbericum
  • Hyperforat
  • Hyperiforce
  • Kira
  • LI 160
  • Neuroplant
  • Psychotonin
  • Sedariston
  • STEI 300
  • WS 5573
  • Ze 117

What is it used for?

Traditional/Ethnobotanical uses

This plant has been used as an herbal remedy for its anti-inflammatory and healing properties since the Middle Ages. Many ancient herbalists, including Hippocrates and Pliny, recorded the medicinal properties of St. John's wort. It was noted for its wound-healing and diuretic properties as well as for the treatment of back pain. In 1633, Gerard's Herbal recorded the plant's use as a balm for burns. The oil of the plant also was popular during this time. An olive oil extract of the fresh flowers that acquires a reddish color has been taken internally for the treatment of anxiety, but also has been applied externally to relieve inflammation and promote healing. Its topical application is believed to be particularly useful in the management of hemorrhoids.

Although it fell into disuse, a renewed interest in St. John's wort occurred during the past decade, and it now is a component of numerous herbal preparations for the treatment of anxiety and depression. The plant has been used in traditional medicine as an antidepressant and diuretic, and for the treatment of stomach inflammation and insomnia.

General uses

A wide range of studies support Hypericum's place in the treatment of depression. Effectiveness is comparable with standard antidepressants, while adverse events are lower than with conventional antidepressants. Interactions with other drugs and quality control issues may limit use. Other areas of therapeutic research for St. John's wort include smoking cessation, premenstrual symptoms, physical symptoms due to mental disorders, and attention deficit hyperactivity disorder, as well as its possible role in treating cancer and HIV.

What is the recommended dosage?

Preparations vary greatly in chemical content and quality, and may be standardized to quantity of hyperforin (commonly 3% to 5%) or hypericin (commonly 0.3%). Clinical trials evaluating the efficacy of St. John's wort in depression have commonly used 900 mg of extract daily in 3 divided doses, both in short-term treatment and for ongoing therapy, for periods of up to 1 year (range, 600 to 1,200 mg/day).


Should not be used with cyclosporine, tacrolimus, irinotecan, and imatinib mesylate, as well as protease inhibitors and nonnucleoside reverse transcriptase inhibitors in HIV treatment.


Avoid use. The use of St. John's wort in depression associated with childbirth has been considered; however, insufficient data on effectiveness or safety argue against its use. St. John's wort should be avoided during pregnancy and lactation until further long-term studies demonstrate a lack of toxicity in the developing fetus and breast-feeding newborn.


St. John's wort has been reported to interact with numerous drugs. Patients should be cautioned on the potential for interactions and the need to consult their health care provider before taking St. John's wort with prescription or nonprescription drugs. Drugs that are most affected should not be used with St. John's wort include protease inhibitors (eg, saquinavir) and nonnucleoside reverse transcriptase inhibitors (eg, nevirapine) used in HIV, and cyclosporine, tacrolimus, irinotecan, and imatinib mesylate. Ethinyl estradiol also may interact with St. John's wort. The risk of developing serotonin syndrome and other CNS adverse reactions cannot be ruled out; extreme caution is needed with combinations of psychotropic medications. Reviews of interactions with St. John's wort are available.

Side Effects

Adverse reactions are usually mild. Potential reactions include dry mouth, dizziness, constipation, and other GI symptoms, and confusion. Sensitivity to sunlight also may occur. In clinical trials, adverse reactions with St. John's wort were usually less than those seen with standard antidepressants. Other possible rare adverse reactions include induction of mental excitement and effects on male and female reproductive capabilities.


Limited information on cell DNA damage exists. A case report exists of an overdose of St. John's wort in a 16-year-old patient consuming 15 tablets (300 mcg strength) per day for 2 weeks, requiring treatment in an intensive care unit.


1. St. John's Wort. Review of Natural Products. Facts & Comparisons Online. March 2010. Accessed April 20, 2010.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.