I am always surprised at what people are willing to believe, and consume, in hopes of becoming skinny. Diet pills- much like a second marriage, they are the triumph of hope over experience.
With regard to herbs, they either have an effect, or they don't. If they do have an effect, they have the potential to be very dangerous as well as helpful. If they don't have an effect, then they are a waste of money and a scam.
I feel the same way about alternative health treatments- TCM (traditional Chinese medicine), acupuncture, naturopathy, homeopathy, massage therapy, chiropractic treatment, etc.
For example, it so happens that I love acupuncture, and it has been effective for me- which means that it could be easily dangerous, in the hands of an unskilled and/or untrained practitioner. In most places, TCM and acupuncture are unregulated, which means that anyone could stick needles in you, manipulate your skeleton through tuina massage, "prescribe" secret remedies of Chinese herbs, etc.
People that assume that because something is natural, it must be "okay", not only are putting themselves in danger, they are likely spending money on crap that could be better used.