Several commonly used herbs and botanical supplements can interfere with blood pressure medications in clinically meaningful ways, either pushing blood pressure dangerously low, making a prescribed drug less effective, or spiking blood pressure on their own. The interactions range from licorice root directly raising blood pressure to green tea slashing the absorption of a widely used beta-blocker. What makes these interactions especially tricky is that many people taking blood pressure drugs also take herbal supplements: surveys in different countries suggest that roughly 60 to 80 percent of people being treated for hypertension use some form of herbal medicine, and many never mention it to their doctor.1PubMed Central. Simultaneous Use of Herbal Medicines and Antihypertensive Drugs Among Hypertensive Patients in the Community: A Review
Licorice Root
Licorice is probably the single herb most consistently flagged by pharmacologists as a problem for people on blood pressure medications. The active compound, glycyrrhizic acid, blocks an enzyme that normally keeps a hormone called cortisol from behaving like aldosterone. When that enzyme is blocked, the body starts retaining sodium and water while losing potassium, mimicking a condition called pseudoaldosteronism. The result is a rise in blood pressure that can be significant enough to send someone to a doctor wondering why their medication stopped working.2JAMA Internal Medicine. Herbal Medicinals: Selected Clinical Considerations Focusing on Known or Potential Drug-Herb Interactions
The interaction is particularly concerning for people taking spironolactone, a potassium-sparing diuretic used for resistant hypertension and heart failure. Spironolactone works by blocking aldosterone’s effects, so licorice essentially pushes the system in the opposite direction, undermining the drug’s entire mechanism.2JAMA Internal Medicine. Herbal Medicinals: Selected Clinical Considerations Focusing on Known or Potential Drug-Herb Interactions The good news is that the hypertension tends to resolve within a couple of weeks of stopping the licorice. The bad news is that licorice root shows up in places you might not expect: herbal teas, throat lozenges, some traditional digestive remedies, and certain candies imported from Europe. If you are on any antihypertensive drug, but especially spironolactone, checking ingredient labels for “licorice root,” “glycyrrhiza,” or “glycyrrhizic acid” is worth the few seconds.
St. John’s Wort
St. John’s Wort is one of the most widely studied herbal products for drug interactions, and the news is consistently bad for people on prescription medications. It powerfully activates a set of liver enzymes responsible for breaking down drugs, particularly the cytochrome P450 system and a transporter protein called P-glycoprotein. When those enzymes are ramped up, they chew through many common drugs faster than intended, lowering the amount of active medication in your bloodstream.3PubMed. Herb-drug interactions: an overview of the clinical evidence
For blood pressure specifically, this means that certain antihypertensive drugs may not reach the concentrations your doctor expected when writing the prescription. Calcium channel blockers like nifedipine and amlodipine are metabolized by these same enzyme pathways and are vulnerable. The interaction is well-enough established that many drug reference guides list St. John’s Wort as a substance to avoid with calcium channel blockers. The broader lesson here is that St. John’s Wort is a prolific interactor: it has documented interactions with dozens of medications across many classes, from blood thinners to oral contraceptives to immunosuppressants. If you are on any prescription medication, treating St. John’s Wort as off-limits is a reasonable default.
Green Tea and Beta-Blockers
Green tea is one of the more surprising entries on this list because it is widely considered a healthy beverage. But a study in healthy volunteers found that drinking green tea dramatically reduced the blood levels of nadolol, a commonly prescribed beta-blocker. The mechanism involves green tea inhibiting a transport protein in the intestine that normally helps nadolol get absorbed into the bloodstream. With that transporter blocked, much of the drug passes through the gut without ever reaching the blood.4PubMed. Green tea ingestion greatly reduces plasma concentrations of nadolol in healthy subjects
Animal research confirmed the finding and identified the specific compound responsible: EGCG, the catechin that dominates green tea’s polyphenol profile. In rats, pretreatment with green tea extract slashed the peak blood concentration of nadolol by about 85 percent and the overall drug exposure by roughly 74 percent.5Phytomedicine. Effects of green tea extract and (−)-epigallocatechin-3-gallate on pharmacokinetics of nadolol in rats Those are enormous reductions. A beta-blocker that barely reaches your bloodstream cannot control your heart rate or blood pressure effectively.
This does not mean a single cup of green tea will render your medication useless, and the research specifically studied nadolol rather than all beta-blockers. But if you drink green tea regularly and are on nadolol or a similar beta-blocker, the interaction is worth raising with your prescriber. Concentrated green tea supplements, which pack far more EGCG per dose than brewed tea, would amplify the concern.
Grapefruit
Grapefruit is technically a fruit rather than an herb, but it appears so often in herbal and “natural health” contexts that it deserves a place here. Grapefruit juice contains compounds called furanocoumarins that permanently disable an intestinal enzyme responsible for breaking down many drugs on their first pass through the gut. When that enzyme is knocked out, more of the drug enters your bloodstream intact than your body is designed to handle.6PubMed. Grapefruit-drug interactions
The drugs most affected include calcium channel blockers, a major class of blood pressure medication. Felodipine is the most studied example: grapefruit juice can roughly triple its blood levels, turning a normal dose into an effective overdose. Other calcium channel blockers in the same family, including nifedipine and amlodipine, are affected to varying degrees. Statins, which many hypertensive patients also take, are among the other affected drug classes.7PubMed Central. Medicinal importance of grapefruit juice and its interaction with various drugs The practical upshot is straightforward: if you take a calcium channel blocker, avoid grapefruit and grapefruit juice. Other citrus fruits like Seville oranges share some of the same furanocoumarins, though regular sweet oranges and lemons are generally fine.
Bitter Orange and Yohimbine
Some herbs raise blood pressure on their own through stimulant activity, which directly works against whatever your medication is trying to accomplish. Bitter orange (Citrus aurantium), found in weight-loss and “energy” supplements, contains synephrine, a compound chemically similar to ephedrine. A controlled study found that a single dose of bitter orange raised systolic blood pressure by about 7 mmHg more than placebo, with the effect lasting several hours. Heart rate also went up.8PubMed. Blood pressure and heart rate effects following a single dose of bitter orange For someone already struggling with high blood pressure, adding a substance that reliably pushes it higher defeats the purpose of taking medication in the first place.
Yohimbine, derived from the bark of an African tree and marketed for everything from weight loss to sexual performance, is another stimulant herb linked to blood pressure spikes. Case reports describe patients presenting with hypertensive urgency after taking yohimbine-containing supplements, with blood pressure elevated to dangerous levels.9PubMed. Hypertensive Urgency: An Undesirable Complication of a “Male Performance” Herbal Product Yohimbine works by blocking a receptor that normally helps keep blood vessels relaxed, so its blood-pressure-raising mechanism is direct and pharmacological, not just a caffeine-like jolt. Both of these herbs are found in multi-ingredient supplements where they may not be prominently labeled, making it important to read the full ingredient list on any supplement you take alongside blood pressure medication.
Garlic Supplements
Garlic sits on the opposite side of the risk spectrum from licorice and bitter orange. Rather than raising blood pressure, garlic has a modest blood-pressure-lowering effect on its own, which means it can add to the effect of your prescribed medication and potentially push your blood pressure too low. Clinical studies suggest that garlic supplementation may reduce blood pressure, particularly in people with mild hypertension.10PubMed Central. Garlic and Hypertension: Efficacy, Mechanism of Action, and Clinical Implications
This additive effect is not always harmful. In fact, some researchers have explored garlic as a complementary approach to blood pressure management. The problem comes when the combined effect is unintended. If your doctor titrated your medication to bring your blood pressure to a specific target, adding a garlic supplement could overshoot that target. Symptoms of blood pressure that drops too low include dizziness, lightheadedness, and fainting, especially when standing up. Cooking with garlic in normal culinary amounts is unlikely to cause this kind of problem, but concentrated garlic capsules or aged garlic extract deliver far more of the active compounds per dose than a few cloves in your dinner.
Ginkgo Biloba
Ginkgo biloba occupies a murky middle ground. It is one of the most popular herbal supplements worldwide, taken primarily for memory and cognitive function, and it has known effects on blood vessel dilation and blood clotting. Research has raised concerns that ginkgo may interact with specific classes of blood pressure medications, though the evidence is not fully settled.11PubMed Central. Effect of ginkgo biloba on blood pressure and incidence of hypertension in elderly men and women
One specific interaction that has been documented involves ginkgo and thiazide diuretics, a very commonly prescribed class of blood pressure drugs. Adverse event reports have described cases of hypertension developing when ginkgo was taken alongside a thiazide.12PubMed. Cardiovascular pharmacotherapy and herbal medicines: the risk of drug interaction The mechanism is not entirely clear, which makes the interaction harder to predict. Until more data are available, people on thiazide diuretics in particular should flag ginkgo use with their doctor. Beyond blood pressure, ginkgo is also known to affect platelet function, so people on blood thinners face an additional layer of risk.
Potassium-Rich Herbs and Your Kidneys
Several common herbs, including alfalfa and dandelion, contain substantial amounts of potassium. For most people, this is harmless. But for people taking certain blood pressure medications that also raise potassium levels, the extra load can tip the balance into hyperkalemia, a condition where blood potassium climbs high enough to disrupt heart rhythm.13HeartRhythm Case Reports. Complete heart block without ventricular escape secondary to hyperkalemia induced by herbal tea
The medications that raise this concern include ACE inhibitors (like lisinopril and enalapril), angiotensin receptor blockers (like losartan and valsartan), and potassium-sparing diuretics (like spironolactone, the same drug that licorice antagonizes). All of these drugs tend to increase blood potassium as part of their mechanism. If you layer on herbal teas or supplements rich in potassium, you are adding to a pot that is already being filled. Dandelion tea is particularly common and often consumed casually without anyone thinking of it as a “supplement,” but the potassium content in concentrated preparations can be meaningful. People with reduced kidney function face even higher risk because their kidneys are less able to clear the excess.
Ginseng
Ginseng is one of those herbs where the reputation for affecting blood pressure is stronger than the evidence behind it, at least for certain varieties. A controlled trial of North American ginseng in people with hypertension found that it had an essentially neutral effect on blood pressure overall.14PubMed. North American ginseng exerts a neutral effect on blood pressure in individuals with hypertension However, Asian ginseng (Panax ginseng) and North American ginseng (Panax quinquefolius) are different species with different active compound profiles, and extrapolating between them is risky.
Comprehensive reviews of herbal products and cardiovascular drugs list ginseng among herbs that can either potentiate or antagonize the effects of blood pressure medications, depending on the species, the dose, and the specific drug involved.15PubMed Central. Cardiovascular Effects of Herbal Products and Their Interaction with Antihypertensive Drugs—Comprehensive Review This bidirectional uncertainty is itself a reason for caution. If your doctor cannot predict which direction the interaction will go, the safest choice is to avoid it or to use it only with monitoring.
Why Your Supplement Label Will Not Warn You
Unlike prescription drugs, herbal supplements in the United States do not undergo premarketing review by the FDA for purity or potency. Manufacturers are not required to prove that a supplement is safe or effective before selling it, and they are not required to list potential drug interactions the way prescription drug labels do.16PubMed Central. Clinical Implications of Herbal Supplements in Conventional Medical Practice: A US Perspective This means you can buy a product that directly interferes with your blood pressure medication without any warning on the packaging.
The regulatory gap creates another problem: variability. Two bottles of “ginseng extract” from different manufacturers may contain very different amounts of active compounds, or different ginsenoside profiles entirely. A review of natural health products and blood pressure found that the clinical significance of many herb-blood pressure interactions remains unclear specifically because of this variability in the chemical content of different preparations.17PubMed. Effects of natural health products on blood pressure A dose that was harmless from one brand might be enough to cause a problem from another. This is very different from the pharmaceutical world, where every pill of the same drug contains a verified amount of the active ingredient.
How Often People Mix Herbs and Blood Pressure Drugs
The gap between awareness and behavior on this topic is striking. In a survey at hypertension clinics in Trinidad, about 60 percent of patients reported using herbal medicines.18PubMed Central. Herbal medicines and blood pressure control among hypertensive individuals across two of trinidad’s regional health facilities A U.S.-focused study found a similar prevalence of 62 percent for herbal or dietary supplement use among people being treated for hypertension.19PubMed Central. Herbal or Dietary Supplement Use and Hypertensive Medications: Does the Combination Relate to Medication Adherence and Blood Pressure Control? And a broader review reported that in some countries, up to 80 percent of hypertensive patients use herbal medicines, sometimes instead of and sometimes alongside their prescribed drugs.1PubMed Central. Simultaneous Use of Herbal Medicines and Antihypertensive Drugs Among Hypertensive Patients in the Community: A Review
Yet most people do not tell their doctors about it. That same review highlighted the lack of communication between patients and healthcare workers as a driver of unsafe co-use. An emergency department study that screened patients for potential herb-drug interactions found that about 20 percent of hypertensive patients reported regular herbal use, and potential interactions were identified among them.20PubMed. Are emergency department patients at risk for herb-drug interactions? The most practical step you can take is simply telling your prescriber everything you take, including teas, supplements, and anything you think of as “just natural.” Your pharmacist is another good resource for catching interactions, but only if they know the full picture.
A Quick-Reference List
The herbs and botanicals covered above fall into a few different patterns of interaction. Knowing which pattern applies can help you understand why a particular combination is risky:
- Raise blood pressure directly: Licorice root, bitter orange, yohimbine. These work against your medication by pushing blood pressure up through their own pharmacological activity.
- Lower blood pressure additively: Garlic supplements. These add to your medication’s effect and can cause blood pressure to drop too low.
- Speed up drug metabolism: St. John’s Wort. This ramps up the enzymes that break down your medication, leaving less active drug in your system.
- Block drug absorption: Green tea (specifically with nadolol and possibly other beta-blockers). This prevents the drug from getting into your bloodstream in the first place.
- Slow drug metabolism: Grapefruit. This disables enzymes that clear the drug, causing drug levels to build up higher than intended.
- Add potassium load: Alfalfa, dandelion. These can push potassium levels dangerously high when combined with ACE inhibitors, ARBs, or potassium-sparing diuretics.
- Unpredictable or bidirectional: Ginseng, ginkgo biloba. These may raise or lower blood pressure depending on the species, preparation, dose, or co-administered drug, making the outcome hard to forecast.
This list is not exhaustive. New herbal products enter the market constantly, and research on herb-drug interactions lags far behind the pace of consumer use. Any time you start a new supplement or herbal product, and you are on blood pressure medication, the default approach should be to check with your pharmacist or prescriber first. The interaction you catch before it happens is always easier to manage than the one you discover in an emergency room.