Additional diagnoses

I remember an instructor stating that it is proper to code "additional diagnoses" that the doctor states the patient has if they are being treated for that condition while hospitalized. I asked if I should code for diagnoses that the patient was not admitted for-- but had when admitted, and was receiving prescription medication for while in the hospital. She said yes. It has been a few years since I had to do inpatient coding and am double checking to make sure this is correct.

So, if an inpatient is admitted for one thing, but is simply getting medication for other diagnoses the doctor states the patient has, is it proper to code them?

Additional diagnoses