Ben Goldacre
Thursday November 11, 2004
The Guardian

· Ah, Susan Clark of the Sunday Times (What’s the Alternative?), how I love her. This time she’s giving advice about which natural substances are safe to take with warfarin. First, she bemoans the dearth of research on the subject. Then she ignores the useful stuff in what we do know. “As a simple guideline, patients who are taking warfarin should avoid any natural remedies that have an action on the cardiovascular system.” I have no idea where that idea came from: but warfarin is famous for being interfered with by other drugs. St John’s Wort, for example, is a very popular drug – herb, collection of drugs in a plant, whatever – that reduces the plasma concentration of warfarin, along with phenytoin and rifampicin: that’s not because they’re active on the cardiovascular system, that’s probably because they interfere with liver enzymes, which means it makes them work harder. Those enzymes also break down warfarin, so if they’re working harder, they break down the warfarin more too, so there’s less of it around in your blood, and you’re more likely to have another nasty clot and die. Likewise, ginseng reduces the plasma levels of warfarin, so they shouldn’t be mixed either. And lots of others.

· So: stand by for the kind of nerdy, and usefully boring science story you’ll see in a paper when I am prime minister of the world government. In a recent study, 2,600 patients on warfarin were sent a questionnaire on what alternative therapies they took: 1,360 responded (believe me, that’s a high response rate) and a whole 19.2% of those responders were, it turned out, taking one or more complementary therapies. Ninety-two per cent of them hadn’t thought to mention this to their doctor. Only 28.3% of all respondents had even thought that herbal medicines could interfere with prescription drugs. Because hardly anybody’s telling them. And, the patients who were taking the complementary therapies – the ones you’d hope would be aware of the risks – were even less likely to think they might interfere with prescription drugs (at a statistical significance of P<0.001, which means there’s a one in 1,000 possibility of that finding occurring by chance).

· Now, doctors have a responsibility to ask about alternative therapies. Patients have a responsibility to themselves to volunteer the information. And the PR arm of the alternative therapy industry, the ones who write articles in national newspapers, have a responsibility to know their onions, and share their knowledge.