Herb Safety & Interactions
Herb safety and medicine interactions: NIH-sourced cautions for twelve herbs, including St. John's wort, ginkgo, garlic and green tea, plus pregnancy, surgery, liver and allergy advice.
Content last updated . This page has not been medically reviewed.
"Natural" does not always mean safe. [1] Herbs can cause side effects, trigger allergies, and change how prescription medicines work. This page summarizes what NIH says for twelve herbs. It is education, not personal advice. Do not stop a prescribed medicine, or use an herb in place of medical care, without talking to a clinician.
Cautions by herb (NIH summaries)
| Herb | Main cautions named | Interactions named |
|---|---|---|
| St. John's wort | Skin reactions after sun; dizziness, trouble sleeping; may be unsafe in pregnancy; infant colic and drowsiness if breastfeeding [2] | Weakens many medicines (some antidepressants, birth control pills, cyclosporine, seizure medicines, digoxin, HIV and cancer medicines, warfarin, some statins); serotonin-related risks with antidepressants [2] |
| Ginkgo | Seeds toxic; dizziness, stomach upset, headache; may be unsafe in pregnancy [3] | May increase bleeding with anticoagulants such as warfarin [3] |
| Garlic supplements | Odor, stomach upset, allergy; raw garlic on skin can burn; may not be safe in pregnancy at food-exceeding amounts [4] | May increase bleeding risk with anticoagulants and aspirin; tell providers before surgery [4] |
| Green tea extract | Liver injury reported (mainly capsule extracts); caffeine; raised blood pressure [5] | Nadolol, atorvastatin and raloxifene reported; may affect other medicines [5] |
| Turmeric / curcumin | Liver damage reported with highly bioavailable products; may be unsafe in pregnancy [6] | Not detailed by NIH [6] |
| Valerian | Headache, dullness, vivid dreams; withdrawal if stopped abruptly after chronic use; rare liver injury [7] | Should not be taken with alcohol or sedatives [7] |
| Chamomile | Allergy (ragweed family), possible severe reactions; estrogen-like effects [8] | Warfarin and some liver-processed medicines reported; birth control pills; theoretical with sedatives [8] |
| Echinacea | Allergic reactions, which may be severe; rashes in children [9] | Conflicting for liver-processed drugs; theoretical with immunosuppressants and caffeine [9] |
| Milk thistle | Digestive upset; allergy (ragweed family); product quality concerns [10] | Not detailed by NIH [10] |
| Elderberry | Raw or unripe berries and other parts are poisonous [11] | Not detailed; NIH advises talking to your provider [11] |
| Ginger | Abdominal discomfort, heartburn, diarrhea [12] | Not detailed by NIH [12] |
| Saw palmetto | Mild digestive effects, dizziness, headache; may be unsafe in pregnancy and breastfeeding [13] | Not detailed by NIH [13] |
"Not detailed by NIH" means the page we read does not list one, not that none exist. Ask a pharmacist.
Documented vs theoretical
Some interactions are reported in people (for example St. John's wort and birth control pills, or chamomile and warfarin). Others are described as theoretical, based on how an herb is thought to act (for example chamomile with sedatives, echinacea with caffeine). [2][8][9] Treat both as reasons to ask, not as proof either way.Surgery and bleeding
Certain supplements may increase bleeding risk or affect response to anesthesia. Talk to your providers as far in advance as possible and tell them about everything you take. [1] Garlic and ginkgo have specific bleeding cautions. [4][3]Pregnancy, breastfeeding and children
Many supplements have not been tested in pregnant women, nursing mothers or children. [1] NIH advises avoiding or being cautious with several herbs in pregnancy (see the table), and notes that some children developed rashes in an echinacea trial. [9]Liver
More cases of acute liver damage in people taking dietary supplements are being reported, and it can be severe, require a liver transplant, or be fatal. NIH gives kava as an example. [1] Stop and contact a clinician for fatigue, nausea, poor appetite, dark urine or yellow skin or eyes. [6]Contaminated or mislabeled products
What is on the label may not be what is in the product. The FDA has found prescription drugs, including warfarin and phenytoin, in products sold as supplements. [1]Misidentified and toxic plants
Do not eat a wild plant because a photo or description says it is safe. Some plants, such as raw elderberries and ginkgo seeds, are poisonous. [11][3]Getting help
Follow label instructions. If you have side effects, stop the supplement and contact your health care provider; you can also contact the manufacturer. [1] In the US, Poison Control is 1-800-222-1222; call 911 for collapse, seizure, trouble breathing or inability to wake. [14] Safety concerns can also be reported to the US Department of Health and Human Services Safety Reporting Portal. [1]Frequently asked questions
Can I take herbs with my medicine?
Not always. St. John's wort, for example, weakens many medicines. Ask a pharmacist before combining. [2]
Do I need to tell my surgeon about herbs?
Yes. Some supplements increase bleeding risk or affect anesthesia. [1]
References
- National Center for Complementary and Integrative Health (NIH). Using Dietary Supplements Wisely. Page last updated January 2019.
- National Center for Complementary and Integrative Health (NIH). St. John's Wort: Usefulness and Safety. Page last updated May 2025.
- National Center for Complementary and Integrative Health (NIH). Ginkgo: Usefulness and Safety. Page last updated February 2025.
- National Center for Complementary and Integrative Health (NIH). Garlic: Usefulness and Safety. Page last updated February 2025.
- National Center for Complementary and Integrative Health (NIH). Green Tea: Usefulness and Safety. Page last updated February 2025.
- National Center for Complementary and Integrative Health (NIH). Turmeric: Usefulness and Safety. Page last updated April 2025.
- National Center for Complementary and Integrative Health (NIH). Valerian: Usefulness and Safety. Page last updated May 2025.
- National Center for Complementary and Integrative Health (NIH). Chamomile: Usefulness and Safety. Page last updated November 2024.
- National Center for Complementary and Integrative Health (NIH). Echinacea: Usefulness and Safety. Page last updated November 2024.
- National Center for Complementary and Integrative Health (NIH). Milk Thistle: Usefulness and Safety. Page last updated February 2025.
- National Center for Complementary and Integrative Health (NIH). Elderberry: Usefulness and Safety. Page last updated November 2024.
- National Center for Complementary and Integrative Health (NIH). Ginger: Usefulness and Safety. Page last updated February 2025.
- National Center for Complementary and Integrative Health (NIH). Saw Palmetto: Usefulness and Safety. Page last updated April 2025.
- Poison Control (America's Poison Centers). poison.org. Help line 1-800-222-1222; online tool; call 911 for collapse, seizure, trouble breathing or inability to wake.
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.