St John’s wort: potentially dangerous interactions which consumers should know about

On this blog, I have repeatedly stressed that there is reasonably good evidence to show that some herbal medicines are effective. The one that is probably supported with better evidence than any other is St. John’s wort (SJW). The first systematic review of SJW was published in 1995 and concluded that SJW is an effective symptomatic treatment for various forms of depressions. Meanwhile, many more trials have become available, and the current Cochrane review concludes that the available evidence suggests that the hypericum extracts tested in the included trials a) are superior to placebo in patients with major depression; b) are similarly effective as standard antidepressants; c) and have fewer side effects than standard antidepressants. 

This must be good news for many patients; particularly the fact that SJW is much safer than synthetic antidepressants seems attractive. But don’t be fooled – SJW may still cause harm. If taken on its own, it is almost as safe as placebo, but when it is combined with other drugs, it can powerfully interact and significantly lower the plasma level of a wide range of prescription medicines.

Some proponents of alternative medicine have suggested that this caution is alar@BocktheRobber mist, and they insist that, actually, the danger is minimal. Are they correct? We need data, I think, not opinion.

A new article provides new insights.

The objective of this study was to assess how often SJW is prescribed with medications that may interact dangerously with it. The researchers conducted a retrospective analysis of nationally representative data from the National Ambulatory Medical Care Survey. The study setting was U.S. non-federal outpatient physician offices. Patients who were prescribed SJW between 1993 and 2010 were the subjects. The outcome measures were medications co-prescribed with SJW.

Twenty-eight percent of SJW visits involved a drug that has potentially dangerous interaction with SJW. These included selective serotonin reuptake inhibitors, benzodiazepines, warfarin, statins, verapamil, digoxin, and oral contraceptives.

The authors concluded that SJW is frequently used in potentially dangerous combinations. Physicians should be aware of these common interactions and warn patients appropriately.

There is little to add – perhaps just this: the awareness of physicians is undoubtedly desirable, but it is not enough; as SJW and other herbal medicines are usually self-prescribed, consumers’ awareness of the risks associated with herbal medicines is at least as important, I think.