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Herb Safety & Interactions

Herb safety and medicine interactions in plain language: urgent warning signs first, then NIH-sourced cautions for twelve herbs and links to guides on blood thinners, antidepressants and more.

Content last updated . This page has not been medically reviewed.

Act first if any of these apply.

  • Collapse, a seizure, trouble breathing or being unable to wake someone: call 911 (US). [1]
  • Swallowed something you think may be poisonous, or too much of a product: in the US, Poison Help is 1-800-222-1222. [1] Other countries are listed on Poison Help by Country.
  • Tiredness, nausea, poor appetite, dark urine or yellow skin or eyes while using a herbal product: stop the product and talk with a health care provider right away. NCCIH gives these signs for turmeric and curcumin products. [2]
  • Agitation, fast heartbeat, high temperature or loss of coordination after combining St. John's wort with an antidepressant: these can be signs of serotonin syndrome. See Herbs and Antidepressants. [3]
  • A severe allergic reaction with trouble breathing: call 911 (US). [1] NCCIH notes that allergic reactions to chamomile and echinacea can be severe. [4][5]
Quick answer
Many people believe "natural" products are always safe and good for them. MedlinePlus says this is not necessarily true. [6] NCCIH, part of the US National Institutes of Health, puts it the same way: "natural" does not always mean "safe." [7] Herbs can cause side effects, trigger allergies and change how medicines work. This page is a map. It summarizes what NCCIH says for twelve herbs and sends you to the guide that goes deeper. It is education, not personal advice, and it never replaces a clinician or pharmacist.

If you take any prescription medicine, the safest first step is to ask a pharmacist before adding an herb. Do not stop a prescribed medicine on your own; ask the prescriber or pharmacist. [8]

Guides in this section

If your question is aboutRead
How herbs and medicines affect each otherMore about How herbs and medicines affect each other →
Warfarin, aspirin or other blood thinnersMore about Warfarin, aspirin or other blood thinners →
Antidepressants and St. John's wortMore about Antidepressants and St. John's wort →
Transplant or immune-suppressing medicinesMore about Transplant or immune-suppressing medicines →
Diabetes, blood pressure, cholesterol or heart medicinesMore about Diabetes, blood pressure, cholesterol or heart medicines →
SurgeryMore about Surgery →
Liver injuryMore about Liver injury →
Pregnancy and breastfeedingMore about Pregnancy and breastfeeding →
Poisonous plantsMore about Poisonous plants →

Cautions by herb (NCCIH summaries)

Each row is what one NCCIH page says, and nothing more. "Not named on that page" means the page we read does not list one. It does not mean none exist.
Herb and partMain cautions namedMedicine interactions named
St. John's wort (Hypericum perforatum L.; aerial parts used in extracts) [9][10]Severe skin reactions after sun exposure; diarrhea, dizziness, trouble sleeping, restlessness. May be unsafe in pregnancy. Breastfed infants can have colic, drowsiness and lethargy. [11]Can weaken many medicines, including some antidepressants, birth control pills, cyclosporine, seizure medicines, digoxin, HIV and cancer medicines, warfarin and certain statins. Serotonin-related side effects with some antidepressants. [11]
Ginkgo (Ginkgo biloba L.; leaf extract) [12]Fresh seeds are toxic. Leaf extract: dizziness, stomach symptoms, headache. May be unsafe in pregnancy. [13]May increase bleeding with anticoagulants such as warfarin. [13]
Garlic supplements (Allium sativum L.; supplements) [14]Odor, stomach upset, allergy. Fresh raw garlic on skin can cause chemical burns. May not be safe in pregnancy or breastfeeding above food amounts. [15]May increase bleeding risk with anticoagulants or aspirin; tell your providers before surgery. [15]
Green tea extract (Camellia sinensis (L.) Kuntze; leaf) [16]Liver injury, uncommon, mostly with tablet or capsule extracts. Nausea, constipation and raised blood pressure. No safety concerns reported for the drink in adults. [17]Nadolol, atorvastatin and raloxifene are named. [17]
Turmeric (Curcuma longa L.; rhizome) [18]Liver damage has been reported with highly bioavailable formulations. Supplements may be unsafe in pregnancy. [2]Not named on that page.
Valerian (Valeriana officinalis L.; root and rhizome) [19]Headache, stomach upset, mental dullness, vivid dreams. Withdrawal symptoms after abrupt stopping following long use. Very rare liver injury. [20]Should not be taken with alcohol or sedatives. [20]
Chamomile (Matricaria chamomilla L.) [21]Allergy, more likely if allergic to ragweed, chrysanthemums, marigolds or daisies. Estrogen-like effects. [4]Warfarin and some liver-processed drugs (reported); birth control pills (preliminary); sedatives (theoretical). [4]
Echinacea (Echinacea purpurea (L.) Moench and related species) [22]Allergic reactions, which may be severe. Rashes in some children in a trial. [5]Conflicting evidence for liver-processed drugs; theoretical for immunosuppressants and caffeine. [5]
Milk thistle (Silybum marianum (L.) Gaertn.; extract) [23]Allergic reactions, especially in people allergic to ragweed-family plants. [24]Not named on that page.
Elderberry (Sambucus nigra L.) [25]Raw or unripe berries and other parts of the tree contain poisonous cyanide-producing substances that can cause nausea, vomiting and severe diarrhea. [26]Not named on that page.
Ginger (Zingiber officinale Roscoe; rhizome) [27]Abdominal discomfort, heartburn, diarrhea, mouth and throat irritation. [28]Not named on that page.
Saw palmetto (Serenoa repens (W.Bartram) Small; berries) [29]Mild digestive symptoms, dizziness, headache. May be unsafe in pregnancy or breastfeeding. [30]Not named on that page.

Documented, reported and theoretical

Some interactions are reported in people, such as St. John's wort with warfarin or chamomile with warfarin. Others are described as theoretical, based on how an herb is thought to act, such as chamomile with sedatives or echinacea with caffeine. [11][4][5] Treat both kinds as reasons to ask a pharmacist, not as proof either way. The page on documented, reported and theoretical risks explains the labels.

Surgery

NCCIH says certain dietary supplements may increase the risk of bleeding or affect your response to anesthesia. Tell your providers about everything you take, as far ahead of the operation as possible. [7] Garlic and ginkgo have specific bleeding cautions. [15][13]

Pregnancy, breastfeeding and children

Many dietary supplements have not been tested in pregnant women, nursing mothers or children. [7] Several herbs in the table are described as possibly unsafe in pregnancy. Do not read a blank cell as safe: for chamomile, valerian and milk thistle NCCIH says little is known. [4][20][24]

Liver

NCCIH says more cases of acute liver damage in people taking dietary supplements are being reported. It can be severe, can require an emergency liver transplant, and is sometimes fatal. Kava is NCCIH's example. [7] Green tea extract, turmeric products and very rarely valerian also appear in the table above.

Contamination and mislabeling

What is on the label may not be what is in the product. NCCIH says the FDA has found prescription drugs, including warfarin and phenytoin, in products sold as supplements. A label word such as "standardized" does not necessarily guarantee quality or consistency. [7] See product quality and contamination.

Poisonous plants

MedlinePlus names comfrey and ephedra as herbs that can cause serious harm. [6] Raw elderberries and fresh ginkgo seeds are poisonous. [26][13] Never eat a wild plant because a photo or description says it is safe; ask Poison Help and a local expert instead.

Reporting a problem

If you have side effects, NCCIH advises stopping the supplement and contacting your health care provider. [7] In the US you can report safety concerns through the US Health and Human Services Safety Reporting Portal. [7] See side effects and reporting.

What we did not find

Proper evidence not found, in the sources we read, for a single safe list of "herbs with no interactions." The pages above state interactions for twelve herbs only. We did not read EMA/HMPC or Health Canada statements for this page.

Frequently asked questions

Can I take herbs with my medicine?

Not always. St. John's wort, for example, is described by NCCIH as able to weaken many medicines, including some that are life-saving. [11] Ask a pharmacist before combining, and see how interactions work.

Do I need to tell my surgeon about herbs?

Yes. NCCIH says some supplements may increase bleeding risk or affect anesthesia. [7]

Does "natural" mean safe?

No. NCCIH and MedlinePlus both say that natural does not always mean safe. [7][6]

Is it safe to use herbs in pregnancy?

Many have not been tested in pregnant women. [7] NCCIH describes St. John's wort, ginkgo, turmeric supplements and saw palmetto as possibly unsafe in pregnancy. [11][13][2][30] Ask your prescriber or midwife before using any.

What if a herb makes me feel unwell?

NCCIH advises stopping the supplement and contacting your health care provider. [7] For poisoning concerns in the US, call Poison Help at 1-800-222-1222. [1]

References
  1. Poison Control (National Capital Poison Center, US), poison.org. Read 2026-10-23.
  2. National Center for Complementary and Integrative Health (NCCIH, US), Turmeric, last updated April 2025. Read 2026-10-23.
  3. National Center for Complementary and Integrative Health (NCCIH, US), St. John's Wort and Depression: In Depth, last updated December 2017 (older page). Read 2026-10-23.
  4. National Center for Complementary and Integrative Health (NCCIH, US), Chamomile, last updated November 2024. Read 2026-10-23.
  5. National Center for Complementary and Integrative Health (NCCIH, US), Echinacea, last updated November 2024. Read 2026-10-23.
  6. MedlinePlus, National Library of Medicine (US), Herbal Medicine. Read 2026-10-23.
  7. National Center for Complementary and Integrative Health (NCCIH, US), Using Dietary Supplements Wisely, last updated January 2019. Read 2026-10-23.
  8. MedlinePlus Medical Encyclopedia, Serotonin syndrome. Read 2026-10-23.
  9. GBIF Secretariat, GBIF Backbone Taxonomy match for Hypericum perforatum: accepted name Hypericum perforatum L.. Read 2026-10-23.
  10. Borrelli F, Izzo AA. Herb-drug interactions with St John's wort (Hypericum perforatum): an update on clinical observations. AAPS Journal 2009; PubMed abstract. Read 2026-10-23.
  11. National Center for Complementary and Integrative Health (NCCIH, US), St. John's Wort, last updated May 2025. Read 2026-10-23.
  12. GBIF Secretariat, GBIF Backbone Taxonomy match for Ginkgo biloba: accepted name Ginkgo biloba L.. Read 2026-10-23.
  13. National Center for Complementary and Integrative Health (NCCIH, US), Ginkgo, last updated February 2025. Read 2026-10-23.
  14. GBIF Secretariat, GBIF Backbone Taxonomy match for Allium sativum: accepted name Allium sativum L.. Read 2026-10-23.
  15. National Center for Complementary and Integrative Health (NCCIH, US), Garlic, last updated February 2025. Read 2026-10-23.
  16. GBIF Secretariat, GBIF Backbone Taxonomy match for Camellia sinensis: accepted name Camellia sinensis (L.) Kuntze. Read 2026-10-23.
  17. National Center for Complementary and Integrative Health (NCCIH, US), Green Tea, last updated February 2025. Read 2026-10-23.
  18. GBIF Secretariat, GBIF Backbone Taxonomy match for Curcuma longa: accepted name Curcuma longa L.. Read 2026-10-23.
  19. GBIF Secretariat, GBIF Backbone Taxonomy match for Valeriana officinalis: accepted name Valeriana officinalis L.. Read 2026-10-23.
  20. National Center for Complementary and Integrative Health (NCCIH, US), Valerian, last updated May 2025. Read 2026-10-23.
  21. GBIF Secretariat, GBIF Backbone Taxonomy match for Matricaria chamomilla: accepted name Matricaria chamomilla L.. Read 2026-10-23.
  22. GBIF Secretariat, GBIF Backbone Taxonomy match for Echinacea purpurea: accepted name Echinacea purpurea (L.) Moench. Read 2026-10-23.
  23. GBIF Secretariat, GBIF Backbone Taxonomy match for Silybum marianum: accepted name Silybum marianum (L.) Gaertn.. Read 2026-10-23.
  24. National Center for Complementary and Integrative Health (NCCIH, US), Milk Thistle, last updated February 2025. Read 2026-10-23.
  25. GBIF Secretariat, GBIF Backbone Taxonomy match for Sambucus nigra: accepted name Sambucus nigra L.. Read 2026-10-23.
  26. National Center for Complementary and Integrative Health (NCCIH, US), Elderberry, last updated November 2024. Read 2026-10-23.
  27. GBIF Secretariat, GBIF Backbone Taxonomy match for Zingiber officinale: accepted name Zingiber officinale Roscoe. Read 2026-10-23.
  28. National Center for Complementary and Integrative Health (NCCIH, US), Ginger, last updated February 2025. Read 2026-10-23.
  29. GBIF Secretariat, GBIF Backbone Taxonomy match for Serenoa repens: accepted name Serenoa repens (W.Bartram) Small. Read 2026-10-23.
  30. National Center for Complementary and Integrative Health (NCCIH, US), Saw Palmetto, last updated April 2025. Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.