The following interactions are not theoretical. They are documented in clinical case reports and pharmacological studies, and some have caused serious patient harm. If you take any of these cardiac medications, please review this table carefully and bring any questions to your next appointment.
Nattokinase + Warfarin / Apixaban / Rivaroxaban / Dabigatran
High Risk
Nattokinase has direct fibrinolytic (clot-dissolving) activity. Combined with anticoagulants, it dramatically increases bleeding risk — including intracranial haemorrhage and GI bleeding.
Stop nattokinase immediately if on any anticoagulant. Discuss with your cardiologist before restarting.
St John's Wort + Warfarin
High Risk
St John's Wort induces CYP2C9, the primary enzyme metabolising warfarin. INR falls unpredictably — potentially to sub-therapeutic levels, increasing stroke and clot risk in patients who need anticoagulation.
Absolute contraindication. Do not take St John's Wort with warfarin under any circumstances.
St John's Wort + Digoxin / Amiodarone / Statins
High Risk
CYP3A4 induction reduces plasma levels of digoxin (causing loss of arrhythmia control), amiodarone (loss of antiarrhythmic effect), and multiple statins. In heart transplant patients, ciclosporin levels fall far enough to trigger organ rejection.
Do not take St John's Wort if on any cardiac medication.
Red Yeast Rice + Prescribed Statin
High Risk
Red yeast rice contains monacolin K — chemically identical to lovastatin. Adding it to a prescribed statin is equivalent to doubling your statin dose without medical supervision, increasing myopathy and rhabdomyolysis risk.
Do not combine with any prescribed statin. If intolerant of statins, discuss alternatives with your cardiologist.
High-dose Fish Oil (>3g) + Anticoagulants / Antiplatelets
Moderate Risk
EPA and DHA have mild antiplatelet properties. At doses above 3g/day, this becomes clinically relevant alongside warfarin, NOACs, aspirin, or clopidogrel — increasing surgical and spontaneous bleeding risk.
Discuss with cardiologist before taking high-dose omega-3 alongside anticoagulants or antiplatelets. Standard 1g capsules are generally low-risk.
CoQ10 + Warfarin
Moderate Risk
CoQ10 has a structural similarity to vitamin K and may reduce the effectiveness of warfarin anticoagulation. INR may fall when CoQ10 is started and rise when it is stopped — both scenarios carry clinical risk.
If taking warfarin, check INR more frequently when starting or stopping CoQ10. Inform your anticoagulation clinic.
Berberine + Statins / Beta-blockers
Moderate Risk
Berberine inhibits CYP2D6 and CYP3A4, two major drug-metabolising enzymes. This can increase plasma levels of lovastatin, simvastatin, metoprolol, and other CYP3A4/2D6-metabolised cardiac drugs — increasing side effect risk.
Discuss with your cardiologist before taking berberine alongside cardiac medications.
High-dose Curcumin / Turmeric + Anticoagulants
Moderate Risk
High-dose curcumin (supplement doses, not culinary use) inhibits platelet aggregation and can potentiate warfarin and NOAC anticoagulation, increasing bleeding risk. Cooking with turmeric is not a concern.
Avoid high-dose curcumin supplements if on anticoagulants or antiplatelets. Culinary amounts are safe.
The golden rule: Tell your cardiologist, GP, and pharmacist about every supplement you take — including herbal teas, protein powders, sports supplements, and anything bought from a health food shop or online. Many patients consider supplements categorically different from "medication," but from a pharmacological interaction standpoint, they are not. The interactions above are well-documented in clinical practice. Disclosure costs nothing; undisclosed interactions can cause serious harm.