Excess of anything is harmful,same applies for the energy drinks.Basically energy drinks are same as soft drinks with caffeine,taurine,glucuronolactone and some more calorie content than soft drinks.It also contains herbs like ginkgo,guarana and ginseng which are central stimulants.These side effects noticed are difficulty in sleeping, indigestion, anxiety and palpitations.If these drinks taken on regular basis with no exercises can lead to obesity.If mixed or taken up with alcohol,the results can be fatal .