There has been considerable research in to herbal medicine with new journals published daily. We know that it works but it seems, specifying exactly how, is not always clear. Overall I am consciously a little sceptical about the level of effectiveness reached with herbal remedies. However, if you're consuming these herbs to assist with a particular dysfunction and it works, well you might not care how it works and frankly any progress is progress.
To many Thais in regional areas western medicine is not a choice, it's not readily available and locals don't necessary "believe" in it's effectiveness (kettle of fish there). But the Thais are doing something right, as a nation they have the lowest cardiovascular and heart disease statistics of any Asian country (WHO 2010) and considering health awareness is arguably more about food than exercise in the general public eye (another kettle of fish), we must wonder what the contributing factors are to this overall healthy, fit and happy nation.