Why do you need to lose weight quickly? Doing so usually results in short-term loss but not keeping it off. Losing weight slowly but steadily by permanently altering your diet for the better and increasing your output of energy works long-term. I doubt oolong tea will do a lot for you. While it does contain caffeine, tea also contains balancing relaxants, which is why drinking it generally doesn't affect people the way unbalanced coffee does. So yeah, there are a lot of things that contain some form of speed that will speed your metabolism quickly, but not healthfully. So again, why the rush?