I don't think you need stuff like drugs/injections to do it. Just stunt them while they grow, feed them endless brain damaging entertainment and never give them an opportunity to grow/think for themselves, or cultivate that mindset to distrust/question everything. By constantly hammering a generation for their entire lives that "if you believe X you're one of the good guys!" and then reinforcing that thorough media and public opinions, you'll get a majority of brain-dead people.

What's fascinating to me is how well integrated into society these folks are. They have jobs, a mortgage, drive in cars, travel, etc. But they seem to lack all common sense, and believe 100% whatever the machine tells them.