Whether the child has been diagnosed with a condition that requires medication or not, this question is framed as if he needs to take the medication because if takes this medication he WILL become a gadol, and if not, he will NOT.
There is no magic gadol pill. Many people with great skills are not gdolim, and many people have overcome many challenges and are.
The scenario you are describing is no different from giving a teenager performance enhancing drugs so he will become a star quarterback.