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Herbal Tea and Medicine Interactions: Documented vs Theoretical

Which herbal teas have documented, reported, theoretical or only animal-study interactions with medicines, shown tea by tea with the strength of each source and what is not known.

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

Safety first. Natural products can cause side effects and interact with medicines. Read herbal tea and extract safety before you use anything on this page.

Read this first. St. John's wort (Hypericum perforatum), sold as tea among other forms, is the best-documented herb for serious interactions. NCCIH says combining it with certain antidepressants can lead to a potentially life-threatening rise in serotonin, with symptoms that may include agitation, diarrhea, fast heartbeat, high blood pressure, hallucinations and raised body temperature. [1] Get urgent medical help for those symptoms; in the US, 911 is for collapse, seizure or trouble breathing. [2]

NCCIH's statements are about the herb in general; tea-specific data were not described in the sources we read.

How to read the labels

An interaction claim is only as strong as its source:

  • Documented: clinical studies or regulator statements built on them.
  • Reported: case reports. They show it can happen, not how often.
  • Theoretical: expected from how the plant or medicine works.
  • Preclinical: animals or cells.
  • None reported / no data: the source lists nothing, which is not proof of none.

Tea by tea

Tea (plant)Medicine groupWhat the source saysLabel
St. John's wort (Hypericum perforatum)Antidepressants; many other prescription medicinesSerotonin rise with some antidepressants; can weaken medicines such as warfarin [1]Documented for the herb; tea-specific data not found
Licorice root (Glycyrrhiza glabra)Corticosteroids, diuretics, heart glycosides, stimulant laxatives, blood pressure medicinesNCCIH: corticosteroid interactions reported; EU monograph: may counteract blood pressure medicines and not to be used with these groups [3][4]Reported; regulator caution
Licorice rootMedicines cleared by the CYP3A4 enzymeEU monograph cites clinical studies where glycyrrhizin for 14 days modestly lowered exposure to midazolam and omeprazole [4]Documented for glycyrrhizin; not a tea trial
Licorice-containing herbal teaDiabetes medicine (SGLT2 inhibitor)One case of low potassium with an SGLT2 inhibitor [5]Reported (single case)
Senna leaf (Senna alexandrina)Heart glycosides, heart rhythm medicines, diuretics, corticosteroids, licoriceEU monograph: consult a doctor first because potassium loss can add up [6]Regulator caution
Chamomile (Matricaria chamomilla)Warfarin; medicines processed by the liverNCCIH: reported; a systematic review lists chamomile tea among items with increased bleeding risk on warfarin [7][8]Reported
ChamomileSedatives; birth control pills; transplant medicinesNCCIH: sedatives theoretical, birth control preliminary; EU monograph: CYP450 interactions reported after kidney transplant with high amounts for about two months [7][9]Theoretical / preliminary / reported
Ginger (Zingiber officinale)WarfarinLactMed: may raise bleeding risk; a review also lists ginger; the EU monograph says none known [10][8][11]Reported; sources differ
Hibiscus (Hibiscus sabdariffa)WarfarinOne case of a very high INR after hibiscus tea [12]Reported (single case)
HibiscusDiuretic (hydrochlorothiazide)Extract raised drug levels in rats and rabbits [13]Preclinical
Valerian (Valeriana officinalis)Alcohol, sedatives"Possible though not proven" sleep-inducing effect; not to be taken with them [14]Theoretical
Marshmallow root (Althaea officinalis)Any medicine taken togetherEU monograph: absorption may be delayed; it should not be taken ½ to 1 hour before or after other medicines [15]Regulator caution
Hawthorn (Crataegus)Anticoagulants, digoxin, blood pressure medicinesPossible increase in effect [16]Theoretical
Chinese herbal tea (ingredients not named in the abstract)Cyclosporine, sirolimusToxic drug levels in a transplant patient [17]Reported (single case)
Peppermint, fennel, lemon balm, passionflower, nettle, raspberry leafNot listedEU monographs: "none reported"; lemon balm: "no data available" [18][19][20][21][22][23]None reported / no data

True tea is covered in Functional Foods; NCCIH notes green tea at high doses lowered blood levels of nadolol. [24]

Teas to ask a pharmacist about first

  • Blood thinners such as warfarin: chamomile, ginger, hibiscus and St. John's wort appear in the sources above. See supplements and blood thinners.
  • Antidepressants: St. John's wort. See supplements and antidepressants.
  • Blood pressure, heart and water pills: licorice and senna. Hibiscus lowered blood pressure in a meta-analysis of trials, so ask if you take blood pressure medicine; we did not find in the sources we read a human trial of hibiscus tea together with a blood pressure medicine. [25]
  • Transplant medicines: chamomile and herbal teas of unknown ingredients. See transplant medicines.
  • Sedatives and alcohol: valerian. Hops also can cause sedation and should be avoided with other sedating drugs. [14][26]

What is not known

Proper evidence not found: controlled studies of usual tea-drinking amounts with a named medicine, for most teas. We searched PubMed for herbal tea and drug interaction case reports on 23 October 2026 and found single cases, not trials. [27] Never stop or change a prescribed medicine because of a tea; ask the prescriber or pharmacist. For how interactions are graded, see how interactions work and the pharmacist checking guide.

Frequently asked questions

Which herbal teas interact with warfarin?

A systematic review lists chamomile tea and ginger among items with increased bleeding risk on warfarin, and NCCIH says St. John's wort can weaken warfarin. [8][1] Ask your prescriber or pharmacist before changing any tea.

Can herbal tea interact with antidepressants?

St. John's wort can, according to NCCIH. [1]

Does "none reported" mean a tea is safe with medicines?

No. It means the source lists nothing. Lemon balm's EU monograph says "no data available." [20]

Does licorice tea affect blood pressure medicine?

The EU monograph says licorice root may counteract the action of prescribed blood pressure medicines. [4]

Can I drink marshmallow root tea with my other medicines?

The EU monograph says absorption of other medicines may be delayed and describes separating them by ½ to 1 hour. Ask a pharmacist about your medicines. [15]

References
  1. National Center for Complementary and Integrative Health (NIH). St. John’s Wort and Depression: In Depth. Read 2026-10-23.
  2. Poison Control (US national poison help service). poison.org. Read 2026-10-23.
  3. National Center for Complementary and Integrative Health (NIH). Licorice Root: Usefulness and Safety. Read 2026-10-23.
  4. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). EU herbal monograph on Glycyrrhiza glabra L., G. inflata Bat., G. uralensis Fisch., radix, EMA/HMPC/108399/2024, last revision or adoption 4 March 2026. Read 2026-10-23.
  5. A Case of Hypokalemia Caused by the Consumption of Licorice-Containing Herbal Tea. Cureus. 2025. Single case report. Abstract read 2026-10-23.
  6. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). EU herbal monograph on Senna alexandrina Mill., folium, EMA/HMPC/625849/2015, Revision 1, last revision or adoption 25 September 2018. Read 2026-10-23.
  7. National Center for Complementary and Integrative Health (NIH). Chamomile: Usefulness and Safety. Read 2026-10-23.
  8. Warfarin and food, herbal or dietary supplement interactions: A systematic review. Br J Clin Pharmacol. 2021. Abstract read 2026-10-23.
  9. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). EU herbal monograph on Matricaria recutita L., flos, EMA/HMPC/55843/2011, last revision or adoption 7 July 2015. Read 2026-10-23.
  10. Drugs and Lactation Database (LactMed), National Library of Medicine. Ginger (record as indexed in PubMed). Read 2026-10-23.
  11. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). EU herbal monograph on Zingiber officinale Roscoe, rhizoma, EMA/HMPC/885789/2022, last revision or adoption 7 May 2025. Read 2026-10-23.
  12. Possible Interaction Between Hibiscus and Warfarin Resulting in Severe International Normalized Ratio Elevation: A Case Report. Cureus. 2026. Single case report. Abstract read 2026-10-23.
  13. Herb-drug interaction between the extract of Hibiscus sabdariffa L. and hydrochlorothiazide in experimental animals. J Med Food. 2011. Animal study. Abstract read 2026-10-23.
  14. National Center for Complementary and Integrative Health (NIH). Valerian: Usefulness and Safety. Read 2026-10-23.
  15. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). EU herbal monograph on Althaea officinalis L., radix, EMA/HMPC/436679/2015, last revision or adoption 12 July 2016. Read 2026-10-23.
  16. Drugs and Lactation Database (LactMed), National Library of Medicine. Hawthorn (record as indexed in PubMed). Read 2026-10-23.
  17. Acute drug toxicity related to drinking herbal tea in a kidney transplant recipient. Ren Fail. 2014. Single case report. Abstract read 2026-10-23.
  18. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). EU herbal monograph on Mentha x piperita L., folium, EMA/HMPC/572705/2014, last revision or adoption 15 January 2020. Read 2026-10-23.
  19. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). EU herbal monograph on Foeniculum vulgare Miller subsp. vulgare var. dulce, fructus, EMA/HMPC/372839/2016, Revision 1, last revision or adoption 31 January 2024. Read 2026-10-23.
  20. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). Community herbal monograph on Melissa officinalis L., folium, EMA/HMPC/196745/2012, last revision or adoption 14 May 2013. Read 2026-10-23.
  21. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). Community herbal monograph on Passiflora incarnata L., herba, EMA/HMPC/669740/2013, last revision or adoption 25 March 2014. Read 2026-10-23.
  22. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). Community herbal monograph on Urtica dioica L.; Urtica urens L., folium, EMA/HMPC/508015/2007, last revision or adoption 14 January 2010. Read 2026-10-23.
  23. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). Community herbal monograph on Rubus idaeus L., folium, EMA/HMPC/44211/2012, last revision or adoption 28 January 2014. Read 2026-10-23.
  24. National Center for Complementary and Integrative Health (NIH). Green Tea: Usefulness and Safety. Read 2026-10-23.
  25. Effect of sour tea (Hibiscus sabdariffa L.) on arterial hypertension: a systematic review and meta-analysis of randomized controlled trials. J Hypertens. 2015. Abstract read 2026-10-23.
  26. Drugs and Lactation Database (LactMed), National Library of Medicine. Hops (record as indexed in PubMed). Read 2026-10-23.
  27. National Library of Medicine. PubMed searches run through the NCBI E-utilities on 2026-10-23 (search terms are named in the text). 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.