Herbal Medicines

St. John’s Wort: Uses, Health Benefits, Side Effects

St. John’s wort, scientifically known as Hypericum perforatum is a flowering shrub native to Europe. It gets its name from the fact that it often blooms on the birthday of the biblical John the Baptist. The flowers and leaves of St. John’s wort contain active ingredients such as hyperforin.

St. John’s wort is available as a supplement in teas, tablets, liquids and topical preparations.  St. John’s wort has been used for medical purposes in other parts of the world for thousands of years. St. John’s wort is continually being studied to try to demonstrate its alleged benefits.

How do I take St. John’s wort?

Preparations in the U.S. have different amounts of active ingredient, so be careful to note how much you’re getting in your tablets. Depending on the preparation, St. John’s wort can be taken in any of the following ways:

  • 300 mg three times a day for up to six weeks;
  • 250 mg twice a day for six weeks;
  • 300 to 600 mg three times a day for six weeks;
  • 350 mg three times a day for eight weeks;
  • 300 to 600 mg three times a day for up to 26 weeks;
  • 400 mg twice a day for six weeks.

What are the health benefits of St. John’s wort?

Research on St. John’s wort use for specific conditions shows:

  • Depression. A Cochrane systematic review found that St. John’s wort can be effective in treating major depression. In fact, some research has shown the supplement to be as effective as several prescription antidepressants. It’s unclear whether it’s beneficial in the treatment of severe depression. St. John’s wort appears to be more effective than a placebo (an inactive substance) and as effective as standard antidepressant medications for mild and moderate depression. It’s uncertain whether this is true for severe depression and for time periods longer than 12 weeks.  However, because St. John’s wort interacts with many medications, it might not be an appropriate choice, particularly if you take any prescription drugs.
  • Menopausal symptoms. Some evidence suggests that taking St. John’s wort alone or in combination with black cohosh or other herbs might reduce menopausal symptoms such as hot flashes. St. John’s wort might also be helpful in wound healing,  but there’s not enough evidence to know for certain
  • Somatic symptom disorder. Some studies indicate that St. John’s wort might be beneficial for the treatment of this condition that causes severe anxiety about physical symptoms such as pain, weakness or shortness of breath.
  • Irritable bowel syndrome. St. John’s wort has also been studied for conditions such as irritable bowel syndrome, chronic hepatitis C virus (HCV) infection, HIV infection, and social anxiety disorder, current evidence suggests that St. John’s wort isn’t helpful.
  • Quitting Smoking and ADHD. There’s not enough reliable evidence to know whether St. John’s wort might be beneficial for quitting smoking or improving memory or for many conditions, including anxiety, ADHD, and seasonal affective disorder.

Is St. John’s wort safe to take?

The FDA classifies St. John’s wort as a dietary supplement, not a drug. Therefore, the agency doesn’t test it for safety and effectiveness. Studies have shown that taking St. John’s wort by mouth for up to 12 weeks has seemed to be safe. But because St. John’s wort interacts with many drugs, it might not be safe for many people, especially those who take conventional medicines.

St. John’s wort can weaken the effects of many medicines, including crucially important medicines such as:

  • Antidepressants
  • Birth control pills
  • Cyclosporine, which prevents the body from rejecting transplanted organs
  • Some heart medications, including digoxin and ivabradine
  • Some HIV drugs, including indinavir and nevirapine
  • Some cancer medications, including irinotecan and imatinib
  • Warfarin, an anticoagulant (blood thinner)
  • Certain statins, including simvastatin.

Taking St. John’s wort with certain antidepressants or other drugs that affect serotonin, a substance produced by nerve cells, may lead to increased serotonin-related side effects, which may be potentially serious.

St. John’s wort may cause increased sensitivity to sunlight, especially when taken in large doses. Other side effects can include insomnia, anxiety, dry mouth, dizziness, gastrointestinal symptoms, fatigue, headache, or sexual dysfunction.

There isn’t enough reliable information available to know if St. John’s wort is safe when it’s used topically. It may cause severe skin reactions to sun exposure.

Can I take St. John’s wort during pregnancy?

No, St. John’s wort may not be safe to use during pregnancy or while breastfeeding. It has caused birth defects in laboratory animals. Breastfeeding infants of mothers who take St. John’s wort can experience colic, drowsiness, and fussiness.

Take charge of your health—talk with your health care providers about any complementary health approaches you use. Together, you can make shared, well-informed decisions. Although it is important to tell your health care providers about any complementary health approaches you use, this is especially crucial for St. John’s wort because this herb interacts with so many medicines. Interactions with St. John’s wort can weaken the effects of life-saving medicines or cause dangerous side effects.


Dr. Oche Otorkpa PG Cert, MPH, PhD

Dr. Oche is a seasoned Public Health specialist who holds a post graduate certificate in Pharmacology and Therapeutics, an MPH, and a PhD both from Texila American University. He is a member of the International Society of Substance Use Professionals and a Fellow of the Royal Society for Public Health in the UK. He authored two books: "The Unseen Terrorist," published by AuthorHouse UK, and "The Night Before I Killed Addiction."
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