My sister just lost 8 pounds in a week by taking Sensa. She said it worked by curbing her cravings so she ate less. The second week she didn't do quite as well on it because she was more stressed out. One other thing she mentioned is that you have to keep changing the flavors because each only works for a limited period of time (max a month) before you become too used to it and it doesn't reduce the cravings as much (enough).
She also mentioned that some month's flavors work better than others. She is definitely a fan of month one.
Sensa isn't a supplement per se but rather flavorings you sprinkle on food depending on what you are craving.
I haven't tried it yet, but I'm tempted.