Herbs and Diabetes, Blood Pressure and Heart Medicines
What sources say about licorice, hawthorn, fenugreek, garlic, green tea and St. John's wort alongside diabetes, blood pressure, cholesterol and heart medicines, with limits clearly marked.
Content last updated . This page has not been medically reviewed.
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Licorice (Glycyrrhiza glabra L.) is the herb on this page with the clearest blood pressure warning. A review of 104 case reports says continuous intake of large amounts of liquorice is a widely known cause of pseudo-hyperaldosteronism leading to hypertension and low potassium (hypokalemia), and that some cases cause life-threatening problems such as arrhythmias, muscle paralysis and coma. [1][2] If heavy licorice use is followed by an irregular heartbeat or muscle weakness, seek medical advice promptly. In the US, call 911 for collapse, a seizure or trouble breathing. [3] Do not stop any prescribed medicine on your own; ask the prescriber or pharmacist.
What the sources found
| Herb and form | Medicine group | What the source found | Strength of evidence |
|---|---|---|---|
| Licorice (high-glycyrrhizin products and candy) | Blood pressure and heart medicines, diuretics | The review above links large, continuous intake to high blood pressure and low potassium. [1] NCCIH says interactions between licorice and corticosteroids have been reported. [4] Proper evidence not found, in the sources we read, for a direct test of licorice against blood pressure medicines. Because licorice itself raises blood pressure in these reports, it is a reason to ask. | Case reports and a narrative review |
| Licorice with glycyrrhizin removed (DGL) | Not assessed | NCCIH says oral products without glycyrrhizin might be safe for up to 4 months. [4] | NCCIH statement; "might" |
| Hawthorn (Crataegus monogyna Jacq. and related species) [5] | Digoxin and heart failure medicines | In a small crossover trial with 8 healthy volunteers, a hawthorn leaf-and-flower extract did not significantly alter digoxin pharmacokinetics. [6] NCCIH notes one study in which a specific hawthorn preparation may have caused early risk of heart failure progression, possibly through drug interactions. [7] | Small trial in healthy people; one patient study of unclear cause |
| Fenugreek (Trigonella foenum-graecum L.; seed) [8] | Diabetes medicines | NCCIH says it may help lower blood sugar in type 2 diabetes but many studies were not high quality, and large doses may cause a harmful drop in blood sugar. [9] | Mixed |
| Garlic supplements | Diabetes, blood pressure and blood-thinning medicines | NCCIH says garlic supplements may reduce blood sugar and, on limited evidence, blood pressure to a small extent. [10] It also warns about bleeding with anticoagulants and aspirin. [10] | Small effects; limited |
| Cinnamon | Diabetes medicines | NCCIH says it is unclear whether cinnamon supplements help diabetes. [11] Proper evidence not found, in the pages we read, for cinnamon interactions with diabetes medicines. | Insufficient |
| Green tea extract | Beta-blockers, statins | Green tea at high doses has been shown to reduce blood levels of nadolol, and green tea extract can reduce blood levels of atorvastatin. [12] | Documented for those two medicines |
| St. John's wort | Digoxin, certain statins | NCCIH lists digoxin and ivabradine, and statins such as simvastatin, among medicines it can weaken. [13] MedlinePlus names it among products that may interact with digoxin. [14] | Documented |
Diabetes medicines and low blood sugar
An umbrella review of herbal medicines for type 2 diabetes found moderate to high certainty that ginger and turmeric lowered HbA1c compared with placebo, but said confidence is limited by the low quality of the included reviews. [15] The same authors say careful monitoring for hypoglycaemia is essential when herbal medicines are used with antidiabetic drugs, because there is a current lack of data on herb-drug interactions. [15] That is an authors' caution, not a measured interaction. Tell your prescriber about any herb you use. See herbs for blood sugar and diabetes: what research shows and supplements and diabetes medicines.Blood pressure, cholesterol and heart medicines
Beyond the table, see herbs for blood pressure and cholesterol: what research shows, supplements and blood pressure and heart medicines and supplements and statins. The single-herb guides are licorice root, hawthorn and fenugreek.Surgery
Garlic supplements may increase bleeding risk and NCCIH advises telling your providers before surgery. [10] See herbs before and after surgery.Limits
Our sources are NCCIH summaries, one trial in eight healthy volunteers, and reviews. Strength labels in the table describe those sources only.Frequently asked questions
Does licorice raise blood pressure?
A review of 104 case reports says large, continuous intake can cause pseudo-hyperaldosteronism with hypertension and hypokalemia. [1] The review says liquorice is nowadays mainly used for flavoring candies or soft drinks, so intake is not limited to supplements. [1]
Can hawthorn be taken with digoxin?
In one trial of 8 healthy volunteers, hawthorn did not significantly change digoxin levels. [6] That does not show it is safe for people with heart failure, and NCCIH reports a study where heart failure progressed. [7] Ask your cardiologist or pharmacist.
Can herbs cause low blood sugar with diabetes medicine?
NCCIH says large doses of fenugreek may cause a harmful drop in blood sugar. [9] Reviewers advise careful monitoring for hypoglycaemia with herbs and antidiabetic drugs. [15]
Which herbs affect statins?
NCCIH says green tea extract can reduce atorvastatin levels and St. John's wort can weaken certain statins such as simvastatin. [12][13]
What should I do before adding an herb to my heart or diabetes treatment?
Ask a pharmacist or your prescriber first, and bring the product label. Do not stop a prescribed medicine on your own.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Pregnancy, breastfeeding, children, liver and kidney
References
- Ceccuzzi G, et al. Liquorice toxicity: a comprehensive narrative review. Nutrients 2023; PubMed abstract. Read 2026-10-23.
- GBIF Secretariat, GBIF Backbone Taxonomy match for Glycyrrhiza glabra: accepted name Glycyrrhiza glabra L.. Read 2026-10-23.
- Poison Control (National Capital Poison Center, US), poison.org. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NCCIH, US), Licorice Root, last updated April 2025. Read 2026-10-23.
- GBIF Secretariat, GBIF Backbone Taxonomy match for Crataegus monogyna: accepted name Crataegus monogyna Jacq.. Read 2026-10-23.
- Tankanow R, et al. Interaction study between digoxin and a preparation of hawthorn (Crataegus oxyacantha). Journal of Clinical Pharmacology 2003 (small trial in healthy volunteers); PubMed abstract. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NCCIH, US), Hawthorn, last updated April 2025. Read 2026-10-23.
- GBIF Secretariat, GBIF Backbone Taxonomy match for Trigonella foenum-graecum: accepted name Trigonella foenum-graecum L.. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NCCIH, US), Fenugreek, last updated February 2025. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NCCIH, US), Garlic, last updated February 2025. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NCCIH, US), Cinnamon, last updated November 2024. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NCCIH, US), Green Tea, last updated February 2025. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NCCIH, US), St. John's Wort, last updated May 2025. Read 2026-10-23.
- MedlinePlus, Digoxin, drug information page. Read 2026-10-23.
- Li E, et al. The efficacy and safety of herbal medicines for glycaemic control and insulin resistance in individuals with type 2 diabetes: an umbrella review. BMC Complementary Medicine and Therapies 2025; PubMed abstract. Read 2026-10-23.