Cerebellar Hemorrhage Provoked by Combined Use of Nattokinase and Aspirin in a Patient With Cerebral Microbleeds

This is a single case report, but it carries a useful safety warning about a popular supplement. Nattokinase, derived from fermented soybeans, is marketed for “blood thinning” — and that property can cut both ways.

The report describes a patient already taking aspirin who developed a cerebellar hemorrhage — bleeding into the brain — after a week on nattokinase. Imaging revealed pre-existing cerebral microbleeds, a sign of fragile small vessels. The authors raise the plausible concern that stacking a fibrinolytic supplement on top of an antiplatelet drug, in someone with vulnerable vasculature, may have tipped the balance toward bleeding.

A case report cannot prove causation; it describes one patient and a temporal association. But it illustrates a real principle: “natural” supplements with anticoagulant activity are not free of risk, especially when combined with blood-thinning medications.

We rate the evidence limited by design — a single anecdote. Its value is cautionary rather than conclusive: a reminder that nattokinase is not harmless, particularly for patients on antiplatelet or anticoagulant therapy, who should consult a clinician before combining them.