We're not talking about faith here Adam, we are talking about using a product for it's results. If it works, there is your proof.
However, because direct natural things (like plants, trees, etc) can not have a patent placed on them they are discounted as not "real". They can patent Brand X but that does not stop anyone else from making the same product and then out selling the Brand X. Therefore, it is not lucrative for pharmaceutical companies to put research or time into products made using easily accessible things (like plants, trees, etc.).
I don't care what Harriet Hall says, no offense to her -I've never heard of her as most people have not. For every one book written with a similar opinion as hers there are 30 books written with positive advise on using Homeopathy. So right there is a 30 to 1 proof it is good science. You can always find someone who will disagree. I will even allow you 30 to 1 odds you can find someone. (Probably very generous odds.) Like I said, it works and there is my proof.