St. John’s wort: medication interactions, effectiveness and precautions

St. John’s wort (Hypericum perforatum) has been studied for some depressive symptoms, but preparations are not interchangeable and its medication interactions can be serious.

St. John’s wort refers to Hypericum perforatum. Products may use flowering aerial parts or dry extracts whose composition varies with the plant material and extraction. Two products with the same name may therefore expose you to different amounts.

The European monograph distinguishes established and traditional uses for selected preparations. That regulatory framework does not mean every supplement is suitable for every person or safe to use without checking concurrent medicines. [3]

Some St. John’s wort preparations may help in selected mild-to-moderate depressive disorders, but results are heterogeneous and not definitive. Trials differ in extract, dose, duration and population. [1][2][5]

St. John’s wort should not replace prescribed treatment or delay assessment of depressive symptoms. Worsening mood, suicidal thoughts, unusual agitation or severe symptoms require urgent medical help.

St. John’s wort can reduce the effectiveness of many medicines. It induces liver enzymes and P-glycoprotein, which can speed the elimination of some substances and lower their concentrations. [0][2][3]

Interactions include hormonal contraceptives, anticoagulants, immunosuppressants, some HIV medicines, cancer medicines and cardiovascular drugs. Reduced effectiveness can have serious consequences, including contraceptive failure, transplant rejection or loss of protection from an essential medicine. [2][3]

It can also add to the serotonergic effects of some antidepressants and expose someone to serotonin syndrome. Agitation, confusion, heavy sweating, fast heartbeat, diarrhoea, fever, tremor or muscle rigidity after a combination require prompt medical advice. [3]

Because safety data are insufficient, pregnancy and breastfeeding require professional advice before use; self-medication with a concentrated supplement is discouraged as a precaution. [2][3]

Extra caution is needed with regular treatment, liver disease, bipolar or psychotic disorders, transplant, autoimmune disease or multiple medicines. Children should not receive a preparation without medical advice.

Sun exposure may increase the risk of skin reactions, and digestive or neurological adverse effects are possible. Nausea, diarrhoea, dizziness, agitation or sleep problems deserve attention, especially with concentrated products or combinations. [0][3]

The profile depends on the preparation and hyperforin content. It is therefore unsafe to infer the safety of an extract from a tea or traditional use.

“Natural”, “mood herb” or “immune support” are not guarantees of effectiveness or safety. A study of one extract does not validate another capsule. A product described as low in hyperforin is not a reason to ignore concurrent medicines: European sources stress that the risk is complex. [2][3]

St. John’s wort has been studied, with a possible signal of benefit in some mild-to-moderate depression, but effectiveness depends on the preparation and interactions can reduce medicine effectiveness or cause dangerous effects. The priority is to avoid self-medication and have the exact product checked by a professional.

1. 01NCCIH, St. John’s Wort: Usefulness and Safety, 2025 — https://nccih.nih.gov/health/st-johns-wort
2. 02NCCIH, St. John’s Wort and Depression: In Depth, 2025 — https://nccih.nih.gov/health/st-johns-wort-and-depression-in-depth
3. 03EMA/HMPC, Hypericum perforatum L. herba, 2022-2023 — https://www.ema.europa.eu/en/documents/herbal-monograph/final-european-union-herbal-monograph-hypericum-perforatum-l-herba-revision-1_en.pdf
4. 04EMA/HMPC, Opinion on Hypericum perforatum L. herba, 2023 — https://www.ema.europa.eu/en/documents/herbal-opinion/opinion-hmpc-european-union-herbal-monograph-hypericum-perforatum-l-herba-revision-1_en.pdf
5. 05Cochrane, St John's wort for treating depression, 2008 — https://cochrane.org/de/evidence/CD000448_st-johns-wort-treating-depression