Medication[x].medicationCodeableConcept
The use of this element is preferred over a reference to a Medication resource (element medicationReference). This is to simplfy the technical implementation around drug codes and to be backwardly compatible with HL7v2 and HL7v3 (EPS).
An example of the preferred approach is shown in Identifier and CodeableConcept Reference
The CareConnect approach of using a medicationReference is shown in Resource Reference to a resource