Taking Warfarin to Prevent Stroke: Will Taking Supplements Cause Harm?

Up to 42 per cent of patients taking warfarin, a blood thinner, used herbal or health supplements at the same time.

Out of 100 patients surveyed who were taking warfarin, a blood thinner to prevent stroke and heart attack (myocardial infarction) - 42 took supplements such as Traditional Chinese Medicines, omega-3 fatty acids and glucosamine which could potentially interact with warfarin.

“What was of concern was that close to 60 per cent of these patients who were taking supplements did not inform their healthcare professionals and many of them were elderly patients who may be more sensitive to the effects of warfarin,” says lead author Bandy Qiuling Goh, Clinic Pharmacy Manager, from the Department of Pharmacy, SingHealth Polyclinics (SHP), a member of the SingHealth​ group.

• Since they felt well after ta​king the supplements, they perceived the supplements to be safe for consumption.
• They thought it was not important because their healthcare providers didn’t ask them about it.
• They were afraid that the healthcare provider might ask them to stop taking their supplements.
• They assumed that healthcare providers were not concerned with the use of ‘non-prescription’ supplements.

In fact, warfarin and supplements can interact in many ways. The interactions may increase the risk of bleeding with warfarin or cause warfarin to be ineffective.Below is a list of herbal/health supplements that can interact with warfarin. This list is not exhaustive.

Source: “MOH Clinical Pharmacy Practice Guidelines: Anticoagulation – Warfarin (2006)” & “Drug Information Handbook (International) 18th edition (2009)”.

Patients on warfarin may not be aware of the potential risk of interaction with supplements because they perceive the use of supplements to be innocuous. The study authors advised patients taking warfarin to consult their healthcare provider before taking any supplements, and for the healthcare provider to always educate patients who are on warfarin about the dangers of self-medication with over-the-counter herbs and supplements.

Ref: T12