Hi Percy,
By this definition an herb is a drug, and it is my position that the only measures that matter regarding drugs like herbs and pharmaceuticals are demonstrated safety and effectiveness.
I was involved in the alternative medicine field a few years ago and worked closely with a traditional Chinese herbalist. The herbs were deemed "natural drugs", so therefore effective and safe. The demonstrated safety and effectiveness was evidenced by "thousands of years" of successes, and supported by case studies, testimonials (we had a wall in the clinic dedicated to them), etc.
If the herbs didn't have the desired effect an explanation is found somewhere - such as the patient indulged in the wrong kind of food, had a stressful week, etc. The herb/treatment is not at fault.
Also, some herbs were contra-indicated for pregnancy, migraines, etc. I believed this demonstrated that the herbs had been tested.
If you haven't learned how to think critically - especially how to evaluate evidence - then it all seems perfectly plausible and believable. This is the root of the problem, I think.
Our governments need to regulate these industries. Until then the safety and effectiveness of herbs will continue to be evidenced by testimony and anecdotes.