My 15 Year Old Son Has Been On Concerta Since

my 15 year old son has been on concerta since he was in grade 4. He is adopted and may be pre exposed to alcohol and for sure drugs. He is an elite athlete and we feel that he is not performing at his full potential in sports because of Concerta. We would like to experiment this summer and take him off the drug and see how much quicker his times are in track etc. We are just concerced about impulsivity, and his grades at school if he stays off them when school goes back in sept.. but we feel he could be an International athlete if taken off his meds.. please help.