St. John's Wort Beware of Drug Interactions

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St. John's wort (Hypericum perforatum), also known as Klamath weed, amber touch-and-heal, or goat weed, is a perennial plant native to Europe but now found throughout the US and parts of Canada. Its name refers to the time when it typically blossoms in late June, which is around the time of the feast day of St. John the Baptist. The plant has oval-shaped leaves and golden yellow flowers. Dating back to the Middle Ages, it has been used for a variety of different ailments such as wound-healing, diuresis, pain, and anxiety. Today, St. John's wort is most commonly found in the form of capsules, pills, tinctures, and teas as a dietary supplement for depression and other mood disorders. St. John’s wort is one of the most popular and top-selling herbal products in the United States.

The mechanism of its antidepressant effect has not been fully determined. The most likely therapeutic components appear to be hyperforin and adhyperforin, which block the reuptake of the neurotransmitters serotonin, dopamine, norepinephrine, and GABA. In the human brain, these neurotransmitters have important roles that affect things like mood and are the same ones that many common antidepressant medications target. St. John’s wort also contains several other active components including amino acids, flavonoids, and essential oils. Like many other plant-derived products, the exact amount of these active ingredients may vary based on harvesting, drying, and storage conditions.

Several studies and clinical trials looking at St. John's wort's effectiveness compared to standard antidepressant medications and placebo have produced mixed results. Whether considered effective or not, most studies agree that it has a fairly mild side effect profile compared to synthetic antidepressant medications, making it a popular and attractive option for treating depression. The most commonly reported adverse effects from St. John's wort include gastrointestinal symptoms, fatigue, and dizziness. In rare cases, sensitivity to sunlight may occur after use of St. John’s wort.

Although it seems to be well-tolerated when taken alone, St. John's wort has been shown to cause important drug interactions with several medications by interfering with drug metabolism pathways. The activity of medications such as blood thinners, oral contraceptives, anti-seizure drugs, and immunosuppressants may all be affected by the use of St. John’s wort. Some of these drug interactions can be potentially dangerous by causing increased adverse effects or decreased effectiveness of certain medications. Therefore, it is important to always consult your physician before taking St. John's wort, and if you are taking any other medications, you should ask your pharmacist to check for drug interactions.

Many find the idea of using St. John's wort as a "natural" way to treat depression and other ailments appealing; however, natural does not always mean safe. It is important to remember that as an over-the-counter dietary supplement, St. John's wort is not regulated by the US Food and Drug Administration and, therefore, does not undergo scrutiny for safety and effectiveness.

If you think someone has taken too much St. John's wort or is having a bad reaction or drug interaction you can check the webPOISONCONTROL^® online tool or call Poison Control at 1-800-222-1222.

Kristina Yee, PharmD
Certified Specialist in Poison Information