Often even people envolved aren't even aware these technologies are being utilized, to those who are, their position is often simple: you do what we say or we torture you, even in protective custody, as surgery isn't really practical.
That claim falls apart as soon as it touches reality: there are a _lot_ of people who are involved in the drug trade, now and in the past. At some point, one of those people would definitely have had a CT or an MRI on their skull (e.g. my dentist does a whole head CT every 5 years as part of the normal process and insurance pays for it). Surely _one_ of those people would have noticed a brain implant.
This sounds extremely made up.
The tech is adversarially designed, you're assuming the medical supply chains are not compromised, and are dramatically underestimating the sophistication involved here generally.
You can't even assume the people interpreting the results are uncompromised, are trained to interpret results in the context of adversarial technology, or are even physiologically able to accurately interpret what they are looking at. This has it's roots in military intelligence, it's not a trivial compromise.
Do you have literally any proof? Otherwise, this is all just a silly made up story as far as I’m concerned.