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St. John’s Wort (Hypericum perforatum): Side Effects & Dosage

What is St. John’s wort (Hypericum perforatum)-oral, and how does it work (mechanism of action)?

St. John's wort is a commonly used over-the-counter (OTC) dietary supplement that is used to treat mild depression, anxiety, and sleep disorders. St. John's wort is a plant that has bright yellow flowers. A number of compounds that have pharmacological activity including naphthodianthrones (hypericin, pseudohypericin, protohypericin, and cyclopseudohypericin), flavonoids (quercetin, rutin, and luteolin), hyperforin, several amino acidsand tannins have been isolated from St. John's wort.

The exact mechanism of how St. John's wort works to alleviate symptoms of depression is not understood. Hyperforin and hypericin are thought to be the major active components. Studies suggest that hyperforin affect serotonin, norepinephrine, and dopamine which are chemicals that affect mood. Other studies show that hypericum has weak effects on catechol-O-methyl transferase, an enzyme that is responsible for the breakdown of chemicals in the brain including serotonin, norepinephrine, and dopamine. Read product labels and discuss dosing with your doctor before taking this dietary supplement.

What brand names are available for St. John’s wort (Hypericum perforatum)-oral?

St. John's Wort

Is St. John’s wort (Hypericum perforatum)-oral available as a generic drug?


Do I need a prescription for St. John’s wort (Hypericum perforatum)-oral?


What are the side effects of St. John’s wort (Hypericum perforatum)-oral?

The most common side effects associated with St. John's wort treatment are

  • asfunction.

What is the dosage for St. John’s wort (Hypericum perforatum)-oral?

Dietary supplements such as St. John's wort are not regulated by the FDA, and are not subject to rigorous clinical studies that evaluate standardized drug dosages. Read product labels and discuss dosing with your doctor before taking this dietary supplement.

The most common dosage that has been used in the majority of studies is 0.3% hypericin or 5% hyperforin in a dosage of 300 to 400 mg three times daily.

Which drugs or supplements interact with St. John’s wort (Hypericum perforatum)-oral?

: St. John's wort increases activity of several liver enzymes. Consequently, St. John's wort may decrease blood levels of drugs that are metabolized or broken-down by these enzymes. Examples of such drugs are warfarin (Coumadin), fluconazole (Diflucan), voriconazole (Vfend), itraconazole (Sporanox), fentanyl (Sublimaze), digoxin (Lanoxin), birth control pills and many other drugs.

St. John's wort should be avoided in patients taking prescription antidepressants due to the risk of serotonin syndrome. Symptoms of serotonin syndrome include agitation, hyperthermia (extreme body temperature), sweating, rapid heartbeat, and neuromuscular disturbances.

Additionally, St. John's wort may interact with other prescription medications. All patients should speak to their doctor or pharmacist before taking St. John's wort.


According to the USDA, there is no difference between a “portion” and a “serving.”
See Answer

Is St. John’s wort (Hypericum perforatum)-oral safe to take if I’m pregnant or breastfeeding?

Due to the lack of safety data, St. John's wort is not recommended during breastfeeding. It is not known if St. John's wort is excreted into breast milk.

What else should I know about St. John’s wort (Hypericum perforatum)-oral?

How should I keep st. john's wort (Hypericum perforatum)-oral stored?

Capsules and caplets should be stored at room temperature between 15 C and 30 C (59 F and 86 F).

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