Bringing medicine back to the USA from Nuevo Progreso, MX

From the Border Patrol site:
"Declare all drugs, medicinals, and similar products to the appropriate CBP official;
Carry such substances in their original containers;
Carry only the quantity of such substances that a person with that condition (e.g., chronic pain) would normally carry for his/her personal use; and
Carry a prescription or written statement from your physician that the substances are being used under a doctor's supervision and that they are necessary for your physical well being while traveling."