I think most of the herbal ones are homeopathic herbal remedies and as mal said you need to eat a healthy diet anyway! There are others that are diuretics and help to remove water from your body. I have used them in the past as i do retain water but in all honesty they made very little diff to my weight (they did however make my skin dry...not good!) Following advice from this site i have been drinking tons of water and havnt had any probs with water retention since
Not official advice just personal experience!
