Billing for Nurse Visit for Weight Check

We have a patient who comes into the office once a month for a Weight Check, this is scheduled as a Nurse Visit. This patient is on a controlled substance for their weight problem, they are followed by the MD routinely. My question is this, if this patient is being monitored for a weight problem, being given a 28 day script for a controlled substance, why are we not billing for the nurse visits? Is this an instance where we cannot bill for a 99211?

Any input is appreciated.