--- title: "Herbal Products and Drug Interactions | Herbadex" description: "St John's wort can weaken the pill; ginkgo and garlic can increase bleeding. The most important herb–drug interactions according to EMA monographs." language: en url: https://herbadex.com/en/guide/herb-drug-interactions/ source: Herbadex (https://herbadex.com) --- Guides # Herbal Products and Drug Interactions "Natural" does not mean a herb cannot interact with medicines. The interactions below are listed in the herbs' EMA monographs. If you take medicines regularly, tell your doctor or pharmacist before starting a herbal product. Updated: October 15, 2026 ## The herb with the most interactions: St John's wort St John's wort induces drug-metabolising liver enzymes (CYP3A4 and others) and lowers the blood levels of many medicines. - Contraceptive pills: breakthrough bleeding and reduced protection; use an extra method - Anticoagulants such as warfarin, ciclosporin, tacrolimus, HIV and some cancer drugs: combined use is contraindicated - Antidepressants such as sertraline or paroxetine: risk of serotonin syndrome ## Herbs that may increase bleeding Herbs that need care if you take anticoagulants or antiplatelet medicines: - Ginkgo: may change the effect of anticoagulants and antiplatelets; stop 3–4 days before surgery - Garlic preparations: may prolong bleeding; stop 7 days before surgery - Willow bark: may increase the effect of coumarin anticoagulants - Saw palmetto: raised INR reported in a few people on warfarin ## Herbs that delay absorption of medicines Herbs rich in fibre or mucilage can delay the absorption of medicines taken at the same time. Leave at least 30–60 minutes between medicines and psyllium, flaxseed or marshmallow root. For psyllium the EMA specifically names minerals, vitamin B12, digoxin, coumarins, carbamazepine and lithium; diabetes and thyroid medicines may need dose adjustment. ## Other important examples - Green tea (caffeine): may reduce the effect of sedatives - Fenugreek: may lower blood sugar; monitor it if you take diabetes medicines - Ginkgo: not recommended with efavirenz; may raise dabigatran and nifedipine levels - Garlic: must not be combined with saquinavir/ritonavir ## What to do Tell your doctor and pharmacist about every herbal product you use, and mention it before surgery. On Herbadex, each herb card lists the interactions from its monograph under "Safety and interactions". ## Frequently asked questions Can I take St John's wort with the pill? Not recommended. According to the EMA it can reduce the effect of hormonal contraception; users should add another method. Which herbs should I watch on blood thinners? Per EMA monographs: ginkgo, garlic preparations, willow bark and St John's wort; raised INR has also been reported with saw palmetto. Can I take psyllium with my medicines? Not at the same time; leave at least 30–60 minutes because it may delay their absorption. ## Sources 1. [European Union herbal monograph on Althaea officinalis L., radix](https://www.ema.europa.eu/en/documents/herbal-monograph/final-european-union-herbal-monograph-althaea-officinalis-l-radix_en.pdf) EMA HMPC · 2015 2. [Community herbal monograph on Linum usitatissimum L., semen – Revision 1](https://www.ema.europa.eu/en/documents/herbal-monograph/final-community-herbal-monograph-linum-usitatissimum-l-semen_en.pdf) EMA HMPC · 2015 3. [Community herbal monograph on Plantago ovata Forssk., seminis tegumentum – Revision 1](https://www.ema.europa.eu/en/documents/herbal-monograph/final-community-herbal-monograph-plantago-ovata-forssk-seminis-tegumentum_en.pdf) EMA HMPC · 2013 4. [European Union herbal monograph on Salix \[various species including S. purpurea L., S. daphnoides Vill., S. fragilis L.\], cortex – Revision 1](https://www.ema.europa.eu/en/documents/herbal-monograph/final-european-union-herbal-monograph-salix-various-species-including-s-purpurea-l-s-daphnoides-vill-s-fragilis-l-cortex_en.pdf) EMA HMPC · 2017 5. [European Union herbal monograph on Allium sativum L., bulbus](https://www.ema.europa.eu/en/documents/herbal-monograph/final-european-union-herbal-monograph-allium-sativum-l-bulbus_en.pdf) EMA HMPC · 2017 6. [European Union herbal monograph on Trigonella foenum-graecum L., semen – Revision 1](https://www.ema.europa.eu/en/documents/herbal-monograph/european-union-herbal-monograph-trigonella-foenum-graecum-l-semen-revision-1_en.pdf) EMA HMPC · 2021 7. [Community herbal monograph on Camellia sinensis (L.) Kuntze, non fermentatum folium](https://www.ema.europa.eu/en/documents/herbal-monograph/final-community-herbal-monograph-camellia-sinensis-l-kuntze-non-fermentatum-folium_en.pdf) EMA HMPC · 2013 8. [European Union herbal monograph on Hypericum perforatum L., herba – Revision 1](https://www.ema.europa.eu/en/documents/herbal-monograph/final-european-union-herbal-monograph-hypericum-perforatum-l-herba-revision-1_en.pdf) EMA HMPC · 2022 9. [European Union herbal monograph on Ginkgo biloba L., folium](https://www.ema.europa.eu/en/documents/herbal-monograph/final-european-union-herbal-monograph-ginkgo-biloba-l-folium_en.pdf) EMA HMPC · 2015 10. [European Union herbal monograph on Serenoa repens (W. Bartram) Small, fructus](https://www.ema.europa.eu/en/documents/herbal-monograph/final-european-union-herbal-monograph-serenoa-repens-w-bartram-small-fructus_en.pdf) EMA HMPC · 2015 Next guide in series ### [Herbal Products in Pregnancy and Breastfeeding →](https://herbadex.com/en/guide/herbal-products-in-pregnancy/) The EMA does not recommend most herbs it assessed during pregnancy, and some are contraindicated. What to know about herbal products in pregnancy. ## Related herbs ### [Fenugreek](https://herbadex.com/en/herb/fenugreek/) T Traditional use Trigonella foenum-graecum Fenugreek seed is traditionally used before meals for temporary loss of appetite and as a poultice for minor skin inflammation. [Digestion](https://herbadex.com/en/for/digestion/) [Skin & Hair](https://herbadex.com/en/for/skin-hair/) [Seed](https://herbadex.com/en/form/seed/) ### [Saw Palmetto](https://herbadex.com/en/herb/saw-palmetto/) A Strong clinical evidence Serenoa repens Saw palmetto fruit extract may help urinary symptoms of benign prostate enlargement; raised INR has been reported with warfarin. [Men’s Health](https://herbadex.com/en/for/mens-health/) [Clay, Soap & Other](https://herbadex.com/en/form/other/) ### [Ginkgo Leaf](https://herbadex.com/en/herb/ginkgo/) A Strong clinical evidence Ginkgo biloba Standardised ginkgo extract may help age-related cognitive decline and mild dementia; bleeding risk and interactions call for caution. [Energy & Focus](https://herbadex.com/en/for/energy-focus/) [Heart & Circulation](https://herbadex.com/en/for/heart-circulation/) [Dried Herb & Tea](https://herbadex.com/en/form/dried-herb-tea/) ### [Marshmallow Root](https://herbadex.com/en/herb/marshmallow-root/) T Traditional use Althaea officinalis Marshmallow root is soaked in cold water and used to soothe throat irritation with dry cough and mild stomach discomfort. [Respiratory, Throat & Mouth](https://herbadex.com/en/for/respiratory/) [Digestion](https://herbadex.com/en/for/digestion/) [Dried Herb & Tea](https://herbadex.com/en/form/dried-herb-tea/) ### [Psyllium Husk](https://herbadex.com/en/herb/psyllium-husk/) A Strong clinical evidence Plantago ovata Taken with plenty of water, psyllium husk helps soften stools in constipation; keep a gap between it and other medicines. [Digestion](https://herbadex.com/en/for/digestion/) [Heart & Circulation](https://herbadex.com/en/for/heart-circulation/) [Dried Herb & Tea](https://herbadex.com/en/form/dried-herb-tea/) ### [Flaxseed](https://herbadex.com/en/herb/flaxseed/) A Strong clinical evidence Linum usitatissimum Taken with plenty of liquid, flaxseed may help soften stools in habitual constipation; drinking enough fluid with it is essential. [Digestion](https://herbadex.com/en/for/digestion/) [Seed](https://herbadex.com/en/form/seed/) ### [St. John's Wort](https://herbadex.com/en/herb/st-johns-wort/) A Strong clinical evidence Hypericum perforatum St John's wort extract may help with mild to moderate depressive episodes, but it seriously interacts with many medicines, including the pill. [Sleep, Stress & Mood](https://herbadex.com/en/for/sleep-stress/) [Digestion](https://herbadex.com/en/for/digestion/) [Dried Herb & Tea](https://herbadex.com/en/form/dried-herb-tea/) ### [Garlic](https://herbadex.com/en/herb/garlic/) T Traditional use Allium sativum Garlic powder is traditionally used to help prevent hardening of the arteries, and garlic extract to relieve symptoms of the common cold. [Heart & Circulation](https://herbadex.com/en/for/heart-circulation/) [Immunity](https://herbadex.com/en/for/immunity/) [Spice](https://herbadex.com/en/form/spice/) ### [Willow Bark](https://herbadex.com/en/herb/willow-bark/) A Strong clinical evidence Salix spp. Willow bark extract may help with short-term low back pain. It contains salicylates, so it is unsuitable under 18 and with blood thinners. [Joints, Bones & Pain](https://herbadex.com/en/for/joints-pain/) [Immunity](https://herbadex.com/en/for/immunity/) [Dried Herb & Tea](https://herbadex.com/en/form/dried-herb-tea/) ### [Green Tea](https://herbadex.com/en/herb/green-tea/) T Traditional use Camellia sinensis Green tea is traditionally used to relieve fatigue and a feeling of weakness; it contains caffeine and is unsuitable with high blood pressure or ulcers. [Energy & Focus](https://herbadex.com/en/for/energy-focus/) [Dried Herb & Tea](https://herbadex.com/en/form/dried-herb-tea/) This page is for information only and is not medical advice. If you take medication, are pregnant, or have a health condition, talk to your doctor or pharmacist before use.