Prozium is used to "suppress emotion and encourage obedience", though, and there's no drug in Shadowrun that does anything remotely close to this. I would just come up with something as a houserule if that's what you're looking for.
Example:
Prozium
Vector: Injection
Speed: Immediate
Duration: 24 hours
Addiction Type: Psychological
Effects: -X Willpower, Emotion Suppressant
Give it an addiction rate similar to kaf as Preston is able to stop taking it without much issue, but add a note that if you take it for a long time and then stop you might overload on emotion or something.
Make Emotion Suppressant act either as a lowered social limit (i.e. lack of empathy from Chrome Flesh) or some sort of psychosis (i.e. the user is functional but less willing or even unable to make decisions based on emotion). Largely, though, I think this is a drug that needs a heavy dose (heh!) of role playing to work, as I find it hard to quantify in game mechanics how it would affect a character.