Oolong tea is reputed to be a slimming tea but does it really work? There are many who have carried out research into this but generally speaking the samples are very small and the variables are perhaps not controlled as accurately as they should be.
As with all reasearch involving people, each person can react differently to a particular treatment, remedy etc. So there are people out there who swear by coffee to keep them awake. I find it has no effect so in my opinion, it is all in the mind. If you expect it to work then if you are suggestible, as the majority of people are, then it will work i.e. the placebo effect.
I have seen forums in which the slimming effects of Oolong tea are debated, some claim that it has helped them shed a lot of weight and for each one of these there are those who claim it has not. So you need to make your own mind up. If it works for you then great, if not, just enjoy the taste!