St John's Wort interacts with clopidogrel

Reported by Susan Aldridge, PhD, medical journalist

The herbal remedy St John's Wort may amplify the blood-thinning effect of clopidogrel.
There is mounting evidence that many over-the-counter remedies, including herbal medicines, may interact with prescription medications. In a new report, doctors at the University of Michigan say that the antidepressant herbal remedy St John's Wort interacts with the blood-thinning medication clopidogrel.

They looked at six healthy volunteers selected for their reduced response to the blood-thinning properties of clopidogrel. They were given St John's Wort, then given clopidogrel and their blood was tested for platelet aggregation, which is the ability to clot. Low platelet aggregation means the blood is thinner than usual.

All six had reduced platelet aggregation compared to when they received clopidogrel alone. This means that St John's Wort amplifies the blood-thinning properties of clopidogrel. The findings are a wake-up call for those taking clopidogrel to avoid heart attack and stroke. If they are also taking St John's Wort, they should seek medical advice in case the combination thins the blood so much that they are in danger of bleeding.

Source
American College of Cardiology meeting 6th March 2005