Western medicine tends to absorb and use any "alternative" treatments that are proven to be effective. Aspirin is an early example. It was found that the bark of certain trees contained a compound that eased pain. Bayer went to the trouble of isolating the active compound and mass producing a purified version. Many big pharmaceutical companies have departments that test and evaluate "natural" remedies to determine what the active ingredients are.
Most of the "natural" remedies that lie outside of western medicine fall into the category of folk medicine that refuses to die out, despite there being ample evidence that it's bunk. Others, like St John's Wort, are painfully inconsistent in the dosage of active ingredients. Saint John's Wort contains what many claim is a weak MIO inhibitor. The problem is the dosage of that inhibitor varies wildly not just from one brand to the next, but even from one PILL to the next in the same bottle. People using this "natural" remedy are, as a result, self medicating with a drug whose dosage can't be satisfactorily controlled. This is a recipe for disaster, particularly when dealing with ailments like clinical depression.
Finally, there's the myth that "natural" remedies aren't as "dangerous" as science based medicine. For some inexplicable reason, people tend to think that just because a drug is less refined (and thus has more contaminants) it's magically less dangerous. What's more, people often ignore "natural" remedies when discussing potential drug interactions with their doctors.