Pills can be stopped. good luck removing an implant. There is also the fact that the implant itself, competes with natural neuronal development by taking up space, and increasing intercranial pressure which is a growth stop signal. Depending on the nature of said implant, it's mode of operation can be changed at the whimsy of an external party. See the story around "Chop jobs" in System Shock/System Shock 2, where cybernetic implants are posited to be capable of automating a person's physical behaviors even against their own will. The topic is toyed with quite effectively there. It's all a matter of splicing in a bit of biocompatible chip at the right nerve endings.

Very "I have no mouth, yet I must scream."

And pills, for the record aren@t much better. Your mind and mental state are still largely dependent on access to the drug, and if you've ever tried to do anything remotely ambitious while contending with the extra restrictions placed on you w.r.t. Schedule 2 substances; good bloody luck. Though if you've got practices you@re willing to share , I'm all ears.