St. John’s Wort

Medically reviewed by Prof. Giorgi Pkhakadze, MD, MPH, PhD — GMJ Editorial Board

What is St. John’s Wort?

St. John’s Wort (Hypericum perforatum) is a flowering plant that has been used medicinally for over 2,000 years. This yellow-flowered herb, native to Europe but now found worldwide, gets its name from the traditional belief that it blooms around St. John the Baptist’s birthday in late June. The plant contains several bioactive compounds, with hypericin and hyperforin being the most studied for their potential therapeutic effects.

As a dietary supplement, St. John’s Wort is typically available as standardized extracts in capsules, tablets, or liquid forms. It’s one of the most widely researched herbal medicines, particularly for its effects on mood and mental health.

Health benefits & uses

Mild to moderate depression (Moderate evidence): Multiple clinical trials have shown St. John’s Wort may be effective for treating mild to moderate depression, with some studies suggesting it performs similarly to certain prescription antidepressants while causing fewer side effects.

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Seasonal affective disorder (Limited evidence): Some research indicates potential benefits for seasonal depression, though more studies are needed to confirm effectiveness.

Anxiety (Limited evidence): While traditionally used for anxiety, scientific evidence remains limited, with most studies focusing on depression rather than anxiety disorders specifically.

Wound healing (Limited evidence): Topical preparations have been traditionally used for minor wounds and skin conditions, but robust clinical evidence is lacking.

How it works

St. John’s Wort appears to work through multiple mechanisms affecting brain chemistry. The primary active compounds, hypericin and hyperforin, may influence neurotransmitter systems including serotonin, dopamine, and norepinephrine. Unlike selective serotonin reuptake inhibitors (SSRIs), St. John’s Wort seems to have broader effects on multiple neurotransmitter pathways.

Hyperforin is thought to inhibit the reuptake of several neurotransmitters, while hypericin may contribute to the herb’s antidepressant effects through different pathways. The exact mechanisms are still being studied, and the herb’s effects likely result from the combined action of multiple compounds rather than a single active ingredient.

Dosage

Typical dosing for St. John’s Wort extracts ranges from 300-900 mg daily, usually divided into 2-3 doses. Most clinical studies have used standardized extracts containing 0.3% hypericin and/or 3-5% hyperforin.

Common dosing schedules include:

• 300 mg three times daily
• 450 mg twice daily
• 900 mg once daily

There is no established Recommended Daily Allowance (RDA) or Upper Limit (UL) for St. John’s Wort. Effects may take 4-6 weeks to become apparent, similar to prescription antidepressants. Always consult a healthcare provider before starting St. John’s Wort, especially for depression treatment.

Food sources

St. John’s Wort is not typically consumed as a food. The therapeutic compounds are concentrated in supplement preparations made from the flowering tops and leaves of the plant. While the plant grows wild in many regions, it should not be harvested and consumed without proper identification and preparation, as dosing and safety require standardized extracts.

Safety & side effects

St. John’s Wort is generally well-tolerated by most people, but can cause several side effects:

• Photosensitivity: Increased sensitivity to sunlight, potentially causing skin reactions
• Gastrointestinal: Stomach upset, nausea, diarrhea
• Neurological: Dizziness, confusion, fatigue, restlessness
• Other: Dry mouth, headache

The herb can also trigger manic episodes in people with bipolar disorder and may worsen symptoms of ADHD, schizophrenia, and Alzheimer’s disease.

Interactions

St. John’s Wort has significant drug interactions due to its effects on liver enzymes that metabolize medications. It can reduce the effectiveness of many prescription drugs, including:

• Birth control pills
• Blood thinners (warfarin)
• Antidepressants (risk of serotonin syndrome)
• Heart medications (digoxin)
• Immunosuppressants
• HIV medications
• Cancer chemotherapy drugs

Combining St. John’s Wort with other antidepressants or supplements affecting serotonin can cause dangerous serotonin syndrome. Always inform healthcare providers about St. John’s Wort use before starting any new medications.

Who should be cautious

Certain groups should avoid or use St. John’s Wort with extreme caution:

• People taking prescription medications (due to interaction risks)
• Individuals with bipolar disorder or psychosis
• Those scheduled for surgery (discontinue 2 weeks prior)
• People with severe depression or suicidal thoughts
• Pregnant and breastfeeding women
• Children and adolescents

Frequently asked questions

Can I take St. John’s Wort with prescription antidepressants?

No, combining St. John’s Wort with prescription antidepressants can cause dangerous interactions, including serotonin syndrome. Always consult your doctor before making any changes to depression treatment.

How long does it take for St. John’s Wort to work?

Like prescription antidepressants, St. John’s Wort typically takes 4-6 weeks to show full effects. Some people may notice improvements sooner, but consistent daily use for at least a month is usually necessary.

Will St. John’s Wort make me more sensitive to the sun?

Yes, St. John’s Wort can increase photosensitivity, making you more prone to sunburn and skin reactions. Use appropriate sun protection and limit sun exposure while taking this supplement.

Can St. John’s Wort affect birth control effectiveness?

Yes, St. John’s Wort can reduce the effectiveness of hormonal birth control methods, including pills, patches, and rings, potentially leading to unintended pregnancy. Use additional contraceptive methods if taking St. John’s Wort.

Is St. John’s Wort safe for long-term use?

While generally considered safe for short to medium-term use, long-term safety data is limited. Regular medical supervision is recommended for extended use, and periodic evaluation of continued need is advisable.