Hawthorn berry can interact with several categories of prescription medications, primarily those that affect blood pressure, heart function, and bleeding. The biggest risks involve additive effects: hawthorn lowers blood pressure and strengthens heart contractions on its own, so combining it with drugs that do the same things can push those effects too far.
How Hawthorn Affects the Body
Understanding why hawthorn interacts with certain drugs starts with what it does in your body. Hawthorn increases nitric oxide production in blood vessels, which causes them to relax and widen. It also raises calcium levels inside heart muscle cells, which strengthens contractions. These two actions together lower blood pressure while improving how efficiently the heart pumps blood.
Beyond cardiovascular effects, hawthorn has mild blood-thinning properties and may influence platelet activity. It also shows blood sugar-lowering and cholesterol-lowering effects in some studies. Each of these actions creates the potential for overlap with medications designed to do the same thing.
Blood Pressure Medications
The most common concern is combining hawthorn with drugs that lower blood pressure. Because hawthorn relaxes blood vessels through its own mechanism, stacking it with prescription antihypertensives can cause blood pressure to drop lower than intended. This applies to several drug classes:
- Beta blockers (such as atenolol or metoprolol), which slow heart rate and reduce blood pressure
- Calcium channel blockers (such as diltiazem or amlodipine), which relax blood vessels
- Alpha blockers (such as prazosin), which prevent blood vessel constriction
- ACE inhibitors and ARBs, which target the hormone system that regulates blood pressure
Symptoms of blood pressure dropping too low include dizziness, lightheadedness, fainting, and fatigue. The risk is highest when you first start combining hawthorn with one of these medications, or when doses change.
Nitrates for Chest Pain
Nitrate medications like nitroglycerin and isosorbide dinitrate are used for angina and work by widening blood vessels to reduce the heart’s workload. Hawthorn widens blood vessels through a similar pathway, boosting nitric oxide levels. Combining the two can lower blood pressure to dangerous levels. This is one of the more serious potential interactions because nitrates already carry a risk of sudden blood pressure drops on their own.
Erectile Dysfunction Medications
Drugs like sildenafil and tadalafil work by relaxing blood vessels, which is why they carry warnings about blood pressure. Adding hawthorn creates a triple layer of blood vessel relaxation: the medication, the hawthorn, and any baseline blood pressure drugs you may already take. The result can be a steep, potentially dangerous drop in blood pressure. If you use these medications, hawthorn is worth flagging with your prescriber.
Digoxin and Heart Medications
Digoxin is a heart medication that strengthens contractions and controls heart rhythm. Because hawthorn also increases the force of heart contractions, the theoretical concern is that combining them could amplify digoxin’s effects, raising the risk of toxicity. There was also early concern that hawthorn’s flavonoid compounds might interfere with P-glycoprotein, a transport protein that affects how digoxin moves through the body.
However, a randomized crossover trial in healthy volunteers found no significant changes in digoxin blood levels after three weeks of combined use. Digoxin absorption, peak levels, and kidney clearance all stayed essentially the same with and without hawthorn. This is reassuring, but the study was small (eight people) and short. The interaction remains listed in drug databases because the theoretical mechanism is plausible and larger studies haven’t been done.
Blood Thinners and Antiplatelet Drugs
Hawthorn has mild antiplatelet properties, meaning it can slightly reduce the blood’s ability to clot. For most people, this effect alone isn’t significant. But if you’re taking warfarin, aspirin, clopidogrel, or other anticoagulant or antiplatelet medications, the combined effect could increase bleeding risk.
A review published in Proceedings of Baylor University Medical Center classified hawthorn’s evidence for bleeding risk as “high-level” and recommended discontinuing it before surgery. The standard guidance is to stop hawthorn at least two weeks before any scheduled surgical procedure. This is the same timeline recommended for garlic supplements, which affect platelets through a similar mechanism.
A Note on Dosage and Products
Most clinical research on hawthorn uses standardized extracts made from the leaves and flowers, not the berries alone. The most studied extract (WS 1442) is standardized to contain about 18.75% oligomeric procyanidins, with clinical doses ranging from 160 mg to 1,800 mg per day. Over-the-counter hawthorn berry capsules vary widely in their active compound content, and some may contain little of the flavonoids and procyanidins responsible for hawthorn’s cardiovascular effects.
This inconsistency matters for interactions. A weakly concentrated berry supplement poses less interaction risk than a highly standardized leaf-and-flower extract at clinical doses. But because supplement labeling doesn’t always reflect what’s actually in the bottle, it’s difficult to gauge your true exposure. The FDA does not approve dietary supplements before they reach store shelves, so quality control depends entirely on the manufacturer.
Safety Warnings Worth Knowing
One clinical trial (the SPICE trial) raised a concerning signal: patients with heart failure who took 900 mg of hawthorn extract daily as an add-on to standard medications showed signs of earlier disease progression compared to placebo. The National Center for Complementary and Integrative Health notes that one possible explanation is an interaction between hawthorn and the patients’ existing medications, though the exact cause remains unclear.
No studies have tested hawthorn’s safety beyond 16 weeks of use. Common side effects at typical doses include dizziness, nausea, digestive upset, and muscle pain.
The FDA has also issued warnings about products labeled as “tejocote root” (Mexican hawthorn) that actually contain yellow oleander, a toxic plant that can damage the heart, nervous system, and digestive tract. A list of contaminated products was published in January 2024. These products are unrelated to the standard hawthorn extracts used in research but are often marketed alongside them.