How to Check a Herb for Interactions: Trusted Databases and Your Pharmacist
Free official resources for looking up a herb (NCCIH, MedlinePlus, LiverTox, LactMed, FDA), what each can and cannot tell you, and why a pharmacist is the last step.
Content last updated . This page has not been medically reviewed.
Safety first. Supplements can cause side effects and interact with medicines. Read mushroom safety and interactions before you use any mushroom product.
The honest limit first. NCCIH says that for many medicines and supplements there is currently little information on possible interactions, and more research is needed. [1] So a lookup that finds nothing does not mean a combination is safe. It means nothing was found. The reliable last step is a pharmacist or clinician who can see your whole medicine list. [2]
What an interaction can look like
Sources describe two directions. Some supplements decrease the effects of medicines, and others increase them, including unwanted side effects. [1] FDA says certain supplements can change absorption, metabolism or excretion of a medication, so you may get too much or too little of it. [3] Documented examples in the sources we read:| Herb or supplement | Documented example | Source |
|---|---|---|
| St. John's wort | Drugs for HIV/AIDS, heart disease, depression, organ transplants and birth control pills are less effective when taken with it. [3] | FDA consumer update |
| Ginkgo | May increase bleeding risk in people taking anticoagulants such as warfarin. [4] | NCCIH |
| Goldenseal | Metformin levels fell about 25 percent in healthy adults given goldenseal extract plus metformin. [5] | NCCIH |
| Concentrated green tea supplements | Can reduce blood levels of some drugs, such as atorvastatin and nadolol. [1] | NCCIH |
These are examples, not a complete list. See how herb-drug interactions happen and interactions by drug class.
Free official resources and what each is for
| Resource | What it is | Use it for | Limit |
|---|---|---|---|
| NCCIH "Herbs at a Glance" | Brief fact sheets with common names, what the science says, side effects and cautions, and further resources. [6] | A plain-language overview of one herb | Covers a limited list of herbs |
| MedlinePlus "Herbs and Supplements" | A browsable A to Z list that links to fact sheets from NIH and other agencies. [7] | Finding an official page by name | MedlinePlus says herb and supplement information from a commercial database it had linked is unavailable as of July 29, 2025. [7] |
| NIH LiverTox | Information on liver injury from prescription and nonprescription medicines and selected herbal and dietary supplements. [8] | Liver questions, for example green tea extract or turmeric products. [9][10] | Only selected herbal and dietary supplements are included |
| NIH LactMed | A database on medicines used during lactation, with milk levels and possible effects on breastfed infants. [11] | Breastfeeding questions; it includes herb entries such as St. John's wort. [12] | Entries can say there is little published experience, as the St. John's wort entry does |
| FDA Dietary Supplement Ingredient Directory | Links to FDA actions and communications about ingredients found in products labeled as supplements. [13] | Seeing whether FDA has issued a warning or action about an ingredient | Not an interaction checker |
For more on the breastfeeding resource see LactMed explained. Some pharmacies and clinics use subscription interaction tools. The sources we read do not describe them, so we do not review or compare any here.
A step-by-step way to look something up
- Copy the label exactly. Product type, plant name, plant part and form. See botanical names and plant parts on labels. Results for one plant, part or preparation do not carry over to another. [12]
- Search the herb in Herbs at a Glance and MedlinePlus, then in LiverTox if liver disease, alcohol use or liver-processed medicines apply.
- Write down the medicine groups the page names, for example anticoagulants, antidepressants, medicines for diabetes or blood pressure, or immune-suppressing medicines for organ transplants.
- Check the FDA directory if the product is a blend, a weight-loss or sexual-health product, or sold with big claims. NCCIH notes some supplements have been found to contain hidden prescription drugs. [14]
- Take the list to a pharmacist. FDA advises asking a doctor or pharmacist, and asking the pharmacist for the package insert of each prescription medicine. [15] The question checklist helps.
Where extra care applies
NCCIH names two situations where interactions matter most: medicines with a "narrow therapeutic range" (examples listed include warfarin, digoxin, cyclosporine, phenytoin and carbamazepine) and planned surgery. [16] It also notes growing concern that supplements may interfere with cancer and HIV treatments. [17] See herbs before and after surgery and herbs and cancer treatment.What not to do
Do not stop or change a prescribed medicine because of what a web page says. Ask the prescriber or pharmacist. If you think a supplement caused a serious reaction, FDA says to stop using it and file a safety report. [18] See side effects and reporting.Frequently asked questions
Is there one place to check every herb and medicine?
Proper evidence not found, in the NIH, MedlinePlus and FDA pages we read, for a single free tool that covers every herb and medicine. They each cover part of the picture. [6][8]
Does "no interaction found" mean it is safe?
No. NCCIH says there is little interaction information for many medicines and supplements. [1] Ask a pharmacist.
Which medicines need the most care?
NCCIH lists medicines with a narrow therapeutic range (such as warfarin, digoxin and cyclosporine) and says to tell providers about herbal supplements. [16]
Can I use LactMed or LiverTox for any herb?
Only for herbs they include. LiverTox covers selected herbal and dietary supplements, and LactMed has entries for some, such as St. John's wort. [8][12]
Who do I ask if the databases disagree or say little?
A pharmacist or your prescriber. FDA and NCCIH both advise discussing all supplements with them. [15][2]
References
- NCCIH (US), 6 Tips: How Herbs Can Interact With Medicines. Read 2026-10-23.
- NCCIH (US), Know the Science, How Medications and Supplements Can Interact: Interactions With Over-the-Counter Medications. Read 2026-10-23.
- FDA (US), Mixing Medications and Dietary Supplements Can Endanger Your Health (Consumer Update, 2022). Read 2026-10-23.
- NCCIH (US), Ginkgo. Read 2026-10-23.
- NCCIH (US), Know the Science, How Medications and Supplements Can Interact: Some Supplements May Decrease the Effects of Medications. Read 2026-10-23.
- NCCIH (US), Herbs at a Glance. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine), Herbs and Supplements. Read 2026-10-23.
- NIH LiverTox, LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. Read 2026-10-23.
- NIH LiverTox, Green Tea (PubMed record of the LiverTox entry). Read 2026-10-23.
- NIH LiverTox, Turmeric (PubMed record of the LiverTox entry). Read 2026-10-23.
- Tomasulo P, Med Ref Serv Q 2007, LactMed: new NLM database on drugs and lactation. Read 2026-10-23.
- NIH LactMed, St. John’s Wort (PubMed record of the LactMed entry, 2025). Read 2026-10-23.
- FDA (US), Information on Select Dietary Supplement Ingredients and Other Substances (Dietary Supplement Ingredient Directory). Read 2026-10-23.
- NCCIH (US), 5 Tips: What Consumers Need To Know About Dietary Supplements. Read 2026-10-23.
- FDA (US), Drug Interactions: What You Should Know. Read 2026-10-23.
- NCCIH (US), Know the Science, How Medications and Supplements Can Interact: Some Medication-Supplement Interactions Can Be Serious. Read 2026-10-23.
- NCCIH (US), Know the Science, How Medications and Supplements Can Interact: Talk With Your Health Care Providers. Read 2026-10-23.
- FDA (US), How to Report a Problem with Dietary Supplements. Read 2026-10-23.