Several common herbs can interfere with blood pressure medications, either by raising your blood pressure on their own, amplifying the drug’s effect until your pressure drops too low, or changing how quickly your body processes the medication. The 2025 guidelines from the American Heart Association specifically flag herbal supplements as substances that clinicians should ask about when managing high blood pressure, and some, like ephedra and St. John’s wort, are listed as “avoid use.” Here’s what you need to know about the most common offenders.
Licorice Root: A Direct Blood Pressure Raiser
Licorice root is one of the most well-documented herbs to avoid while taking blood pressure medication. The active compound in licorice blocks an enzyme in your kidneys that normally keeps cortisol from acting like aldosterone, the hormone that tells your body to retain sodium and water. When that enzyme is blocked, cortisol floods the same receptors aldosterone would use, and your body starts holding onto salt and fluid as if aldosterone levels were sky-high. The result is a condition called pseudohyperaldosteronism: your blood pressure rises, your potassium drops, and you retain water.
This is especially dangerous if you take diuretics (water pills) for blood pressure. Diuretics work by helping your kidneys flush out sodium and water. Licorice does the opposite. The two can cancel each other out, leaving your blood pressure uncontrolled while also worsening potassium loss. Licorice is found not just in supplements but in some teas, candies, and chewing tobacco, so it can sneak into your routine without you realizing it.
St. John’s Wort: Changes How Your Body Processes Drugs
St. John’s wort, commonly taken for mild depression, is one of the most potent herbal disruptors of drug metabolism. It affects a family of liver enzymes responsible for breaking down a wide range of medications, including several classes of blood pressure drugs. Calcium channel blockers like verapamil, nifedipine, and diltiazem are metabolized through one of these pathways. When St. John’s wort revs up those enzymes, your body clears the medication faster than intended, which can leave you with drug levels too low to control your blood pressure.
The AHA’s 2025 blood pressure guidelines list St. John’s wort in a table of substances that may cause elevated blood pressure and recommend avoiding it. The interaction isn’t limited to one drug class either. St. John’s wort affects at least five major metabolic enzyme pathways, making it a concern with beta-blockers, ACE inhibitors, and other cardiovascular drugs as well. If you’re taking any prescription medication for blood pressure, this herb deserves serious caution.
Hawthorn Berry: Too Much of a Good Thing
Hawthorn is sometimes marketed as a natural heart tonic, and it does have real effects on the cardiovascular system. The problem is that those effects overlap with prescription blood pressure drugs. Hawthorn can lower blood pressure and dilate blood vessels on its own. When combined with beta-blockers like metoprolol, atenolol, or propranolol, hawthorn can amplify their blood-pressure-lowering effects. The result can be blood pressure that drops too far, causing dizziness, fainting, or dangerous lightheadedness, especially when you stand up.
This type of interaction is called an additive effect. Neither substance is “wrong” on its own, but together they push your blood pressure lower than either would alone. If you’re already well-controlled on medication, adding hawthorn could tip you into hypotension without warning.
Garlic Supplements: Safe in Food, Risky in Pills
Garlic eaten as part of a normal meal is unlikely to cause problems. Garlic supplements are a different story. In concentrated doses, garlic can add to the blood-pressure-lowering effect of antihypertensive medications, potentially dropping your pressure too much. The Merck Manual draws a clear line between dietary garlic and supplemental garlic: small amounts in food are generally fine, but the larger doses found in capsules and extracts can interact with blood pressure drugs.
Garlic supplements also have mild blood-thinning properties, which can compound risks if you’re taking medications that already affect clotting.
Ginkgo Biloba: Blood Pressure and Bleeding Concerns
Ginkgo biloba is a popular supplement for memory and circulation, but it interacts with several blood pressure medications. Cleveland Clinic specifically flags interactions with calcium channel blockers like diltiazem, nifedipine, and verapamil. Lab research has shown that ginkgo inhibits the same liver enzyme pathway those drugs rely on for metabolism, which could cause the medication to build up in your system to higher-than-intended levels.
Ginkgo also has antiplatelet properties, meaning it reduces your blood’s ability to clot. If you’re taking blood pressure medication alongside blood thinners or even regular aspirin, adding ginkgo raises the risk of bleeding events. This combination of metabolic interference and blood-thinning effects makes ginkgo one of the more complex herbs to manage alongside cardiovascular medications.
Ephedra and Bitter Orange: Herbal Stimulants
Ephedra (also called Ma Huang) is explicitly listed in the AHA’s 2025 guidelines as an herb to avoid when managing blood pressure. It acts as a stimulant, constricting blood vessels and raising heart rate, which directly works against the goal of antihypertensive medication. Ephedra has been banned from dietary supplements in the U.S. since 2004, but it still appears in some imported products and traditional preparations.
Bitter orange (which contains synephrine, a compound chemically similar to ephedra’s active ingredient) partially filled the market gap after ephedra’s ban. Research findings on bitter orange are mixed. Some studies found no significant effect on blood pressure from a single dose, while others observed small but measurable increases in both systolic and diastolic blood pressure lasting up to five hours. One study noted a significant increase in diastolic blood pressure of about 8.7 mmHg. Even modest, temporary spikes can be a problem if you’re already managing hypertension, especially if bitter orange is taken daily in a weight-loss or energy supplement.
Ginseng: Conflicting but Worth Knowing
Ginseng has a complicated reputation when it comes to blood pressure. An early observational study reported that hypertension developed in 14 adults using ginseng root, which established its reputation as a blood pressure raiser. More recent clinical trials tell a different story. A study published in the AHA’s journal Hypertension found that North American ginseng had a largely neutral effect on blood pressure in people with hypertension, with no overall difference from placebo across a 160-minute monitoring period.
That said, the same study found small, time-specific fluctuations: a slight systolic increase at the 160-minute mark and minor diastolic shifts at other intervals. These effects were small (a few mmHg in either direction) but unpredictable. The concern isn’t that ginseng will dramatically raise your blood pressure. It’s that its effects are inconsistent, and when you’re taking medication calibrated to keep your numbers in a tight range, even small unpredictable shifts can be problematic.
Other Herbs That Warrant Caution
Several additional herbs have shown the ability to interfere with the liver enzymes that metabolize blood pressure drugs. Lab research found that common sage, valerian, horse chestnut, and echinacea all inhibited the same metabolic pathway used by calcium channel blockers, with sage and ginkgo showing particularly strong effects. While these findings come from laboratory studies rather than human trials, they suggest a real potential for these herbs to alter how your body handles certain blood pressure medications.
Dandelion root acts as a natural diuretic. If you’re already taking a prescription diuretic for blood pressure, adding dandelion can compound the water and electrolyte loss, potentially leading to dehydration or dangerous drops in potassium or sodium. Yohimbine, derived from the bark of an African tree and sold for energy or sexual performance, is another substance the AHA specifically flags as capable of raising blood pressure.
Why These Interactions Are Easy to Miss
The core challenge with herb-drug interactions is that herbs aren’t regulated the same way prescription drugs are. Doses vary between brands, active compound concentrations aren’t always standardized, and many people don’t think to mention supplements when talking to a pharmacist or doctor. Some of these herbs appear in combination products (energy blends, weight-loss formulas, sleep aids) where you might not even realize you’re taking them.
If you’re on blood pressure medication, keep a list of every supplement, tea, and herbal product you use and share it during medical appointments. The interactions described above range from mild to genuinely dangerous, and the risk depends on the specific blood pressure drug you take, the herb’s dose, and how your individual body metabolizes both. A pharmacist can cross-check specific combinations and is often the fastest way to get a clear answer about a particular product.