Hawthorn: Side Effects, Contraindications and Interactions, What Studies Show

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Hawthorn, olive extract, black garlic, rhodiola, coenzyme Q10, royal jelly and 750 mg of magnesium bisglycinate per daily dose. Hawthorn is dosed at 200 mg, within the range of clinical trials, as part of a formula designed for blood pressure balance.

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Hawthorn is a hedgerow shrub, Crataegus, whose leaves and flowers are used, sometimes the fruits. Clinical trials mainly tested two standardized extracts of leaves and flowers: one dosed at 18.75% oligomeric procyanidins, the other at 2.25% flavonoids. They were studied in heart failure and hypertension, at doses of 160 to 1,800 mg per day.

A pharmacology review places usual doses between 160 and 900 mg per day of extract, in two or three doses. It is this activity on the heart and vessels, which is sought, that also grounds the precautions. For the benefits, our article hawthorn, blood pressure and palpitations provides an update; this guide focuses on safety.

Controlled trials confirm this tolerability. In a crossover trial in 21 adults with slightly elevated blood pressure, tested up to 2,500 mg per day over short periods, nausea affected 7.9% of participants on hawthorn versus 9.5% on placebo, headaches 15.9% versus 14.3%, palpitations 7.9% versus 4.7%. In 209 heart failure patients followed for 16 weeks, adverse effects were even less frequent at 1,800 mg per day, 26.1%, than at 900 mg, 28.6%, or placebo, 51.4%, notably dizziness.

This result is important for safety: in fragile patients, who were taking a diuretic for 85%, an ACE inhibitor for 83%, a beta-blocker for 64%, and a cardiac glycoside or nitrate derivative for more than half, two years of hawthorn revealed no drug interaction signal, according to a review of extract data published in 2018. The benefit on cardiac events, however, was not demonstrated.

The smaller American HERB CHF trial nuances this picture. In 120 treated heart failure patients, 450 mg of hawthorn twice daily for six months did not improve walking distance, quality of life, or exercise capacity, with a slight gain in ejection fraction. Adverse effects were more frequent than placebo, 60.0% versus 38.3%, but mainly non-cardiac. A secondary analysis found a risk of early worsening of heart failure multiplied by 3.9, based on few events, a signal that SPICE did not find.

To put things in perspective, the 2008 Cochrane review, which combined ten trials and 855 patients, showed a benefit of hawthorn as a complement to treatment on maximum workload, heart oxygen consumption, and shortness of breath, with infrequent, mild, and transient adverse effects. The practical conclusion is consistent from one source to another: in heart failure patients, hawthorn is only taken with the cardiologist's approval.

In people already under treatment, the effect adds on without any detected interaction. In a 16-week trial of 79 type 2 diabetics, 71% of whom were taking blood pressure medications, 1,200 mg of hawthorn daily reduced diastolic pressure from 85.6 to 83.0 mmHg, compared to 84.5 to 85.0 under placebo, with no interaction between the plant and medications. Over a few days, however, the effect is null: in the trial at 2,500 mg daily, neither blood pressure nor arterial dilation changed in three and a half days.

Digoxin. The absence of effect on blood levels does not close the question. In the laboratory, hawthorn increases calcium in cardiac muscle cells, like digoxin, with no additional effect when both are combined, a sign that they act on the same target; it also interferes with one of the digoxin blood assays. A cardiology review considers that hawthorn enhances the activity of digitalis glycosides. With digoxin, hawthorn should only be taken on the advice of a cardiologist.

Beta-blockers, calcium channel inhibitors, nitrate derivatives, erectile dysfunction medications. A pharmacology review mentions possible enhancement of medications that dilate blood vessels or slow the heart rate. No dedicated study was found, another review considers these interactions unproven, and in SPICE, 64% of patients were taking a beta-blocker without any signal. The interaction therefore remains theoretical, but the additive effects on blood pressure and heart rate justify medical consultation.

No human data were found during pregnancy or breastfeeding: the trials excluded these women. In pregnant rats, a dose 56 times higher than the human dose did not disrupt embryonic development, which is insufficient to conclude for humans; the authors of this study note that hawthorn is considered contraindicated during pregnancy in practice, while a pharmacognosy review merely recommends expert consultation. No trials have been conducted in children either. In these three situations, hawthorn should be avoided without medical advice.

When searching for "hawthorn heart danger," you come across cases of cardiac poisoning. They concern weight-loss supplements sold as tejocote root, a Mexican hawthorn, Crataegus mexicana, of which the root is used rather than the leaves and flowers. A 16-year-old who had swallowed eight pieces presented with a heart rate of 38 beats per minute and cardiac conduction disorder, resolved within about thirty hours. DNA and chemical analyses of supplements sold under this name found Indian yellow laurel, a plant highly toxic to the heart, in place of the stated ingredient, and a case published in 2026 describes the same scenario.

These accidents do not concern the standardized extracts of hawthorn leaves and flowers used in trials. They do, however, highlight the importance of traceability: species, plant part, and dosage clearly indicated.

Outside these situations, in healthy adults, the data describe a well-tolerated plant, whose side effects are rare, mild, and similar to those of placebo.

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