I imagine they scale it for the addicts tolerance? I know for alcohol addicts they will prescribe beer and other alcohols but the dosage is correlated with the amount you were consuming before starting treatment. It's basically just a schedule that is backed by medical research for safe rates to get clean.

I think giving them enough to get high just wouldn't really count as treatment, so I agree it is likely the case that they cut the dose way below what the addict would ""Want""