Does St John's wort interact with conventional drugs?

The effect of St John's wort (Hypericum perforatum) on the bioavailability of conventional drugs remains unclear. Reviewing 22 trials, Mills and colleagues (p 27) found that St John's wort either had no effect or decreased the availability of conventional drugs when used together. Most studies used a “before and after” design, and the overall quality of the trials was limited in scope and methodological quality.

Figure 1.