Looking for a good Appetite Suppressant

I am trying to diet but my hunger keeps doing me in so I am looking for a good natural appetite suppressant. I would like one that works well without harmful chemicals. I really want to lose about 40 pounds if I can get this part under control. They said when you have hunger pains you are really just thirsty, but I drink a lot of water and still have hunger pangs. If anyone knows of a good suppressant let me know.