Just a thought on something... given that there are some allergens (for example, Soy) that are not just common but incredibly pervasive in the Shadowrun universe, the people who have those allergies at higher levels would have to pop Zero constantly to avoid having to constantly deal with the nastiness.
Since people also develop tolerance to medications they have to take constantly, not just street drugs, would something like an Addiction: Zero trait be appropriate to show that a person on Zero would have to deal with increased dosages as their body builds up a resistance to the suppressant?