This document sets out guidance for primary care networks (PCNs) implementing the structured medication review (SMR) and medicines optimisation service, as per the requirements set out in the 2020/21 Network Contract Directed Enhanced Service (DES) Specification; which states that PCNs must have due regard to this guidance when delivering the service.  It includes the principles of undertaking a SMR and should be read alongside the DES Specification and the Network Contract DES Guidance.