Perhaps, but I still question the likeliness that the mainstream pot dealer would move to selling pills still distributing from the same source. Pot, cocaine, mdmda, etc are available in bulk from illicit sources. Prescription pills usually come from a legal source at some point and come in smaller quantities. From what I hear opium is more expensive because of the difficulty to transport it in its raw form, and therefore sought after.

Wealthier clients usually have a doctor that will write them the prescriptions for a fee. It's not unfathomable that his dealer also had a line on prescription pills, and he did note that he went dry from time to time but still...