Any negative effects of green coffee bean extract ?

I recently bought the green coffee bean extract for the weight loss (especially my belly fat). I just read about the green coffee bean supplement often leads to anxiety, jitters, sleeplessness and increases heartbeat rate etc.

 I wonder if I really need to consult with doctors and take advices before using it .Also can you refer me any sepecification about its usage daily for a teen guy like me to loose weight effectively without problem.