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St. John's Wort

Medium Risk

Also known as:

goatweed hypericum klamath weed

st. john's wort capsules, flower, and tea
Possible Symptoms
  • dry mouth
  • minor stomach upset
  • nausea and vomiting
  • diarrhea
  • dizziness and confusion
What to Do
  1. Wipe or rinse out the mouth.
  2. Give a serving size of water to drink.
  3. Rinse any exposed skin with lukewarm water and soap.
  4. Call 1-800-222-1222 for additional instructions.


Drug interactions are the main concern with St. John’s Wort because they can alter how the body processes many important medications. This can lead to a change in how the prescription medicine works or can cause dangerous side effects. In general, this substance is tolerated well when taken alone on a **short time basis** and at an **appropriate dose**.  Call your healthcare provider or the Missouri Poison Center at 1-800-222-1222 for questions about your medications and supplements.

Additional Information

Quick Facts about St. John’s Wort:

Caller’s to the poison center ask about the uses of St. John’s Wort and the side effects associated with this supplement.

St. John’s Wort (Hypericum perforatum) is an invasive flowering plant. The bright yellow flowers bloom during the summer solstice in late June. However, it grows naturally in certain climates worldwide, mostly in prairies and pastures, where it is known to be harmful to livestock. This plant is also known as Klamath weed, goatweed, hypericum.

What is It Used For?

Most calls to the poison center about St. John’s Wort are questions about the supplement versus the actual plant. This supplement treats depression, anxiety, and symptoms associated with menopause, such as hot flashes and other mood disorders. It is available in various forms, such as tea, tablets, and topical preparations. As with all supplements & essential oils, it is not FDA approved for these conditions, and there are important safety issues to consider.

St. John’s Wort side effects

Generally, drug interactions are the main concern with this supplement because they can alter how the body processes many important medications. This can lead to a change in how the prescription medicine works or can cause dangerous side effects. In general, St. John’s Wort is tolerated well when taken alone on a short time basis and at an appropriate dose. Additionally, minor symptoms are expected in the case of one-time, accidental ingestion of these supplements. It can cause side effects such as stomach upset, nausea, vomiting, dry mouth, dizziness, confusion, restlessness, headache, and sensitivity to light. Always tell your doctor all medications and supplements you are taking to help avoid drug interactions. Remember, the Missouri Poison Center is also available for drug interaction questions!

Important drug interaction examples with St. John’s Wort include:

  • SSRIs (for depression): There is a risk for the build-up of high levels of serotonin in the body resulting in serotonin toxicity.
  • Amphetamines (for ADHD): This combination can also increase the risk for serotonin toxicity.
  • Benzodiazepines (for anxiety): This combination can decrease the effectiveness of these medicines.
  • Others: birth control pills, chemotherapy drugs, over-the-counter antihistamines, heart medications, and many more.

What to do if there is an exposure

If you find someone has eaten a small amount of the St. John’s Wort plant or misdosed the supplement, do not panic. Wipe out any material from their mouth and give them something to drink. Lastly, if problems start or you have questions, call the Missouri Poison Center right away at 1-800-222-1222. The poison center is open all day, every day, for poisoning emergencies and questions.

**Note: Don’t forget, every case is different. To make sure you are getting the best information for your individual situation, click below to call or chat. Remember, calling is fast, free, and confidential.

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