As the title, a CBM that would automatically inject a drug into your system when it detects that the levels of whatever drug you’ve loaded it with are low in your body.
Alternately an activated CBM (would be a free action) to inject you with whatever drug you’ve previously loaded it with.
Useful for addicts as the initial one, or possibly to keep you good and caffeinated. The second one would apply to more situational drugs. You’d be able to load them, and perhaps it would take longer than just taking the drugs, but you’d be able to get them instantly later.