Addiction Treatment Access Improvement Act of 2018 This bill amends the Controlled Substances Act to revise the qualifications required for a practitioner to administer, dispense, or prescribe narcotic drugs for maintenance or detoxification treatment in an office-based opioid treatment program. It increases the maximum patient limit for a qualifying practitioner who meets certain requirements. The maximum patient limit is the maximum number of patients a qualifying practitioner can treat at one time. The bill expands qualifying practitioners to include additional nonphysician practitioners: clinical nurse specialists, certified registered nurse anesthetists, and certified nurse midwives. It makes permanent the authorization for certain nonphysician practitioners to become qualifying practitioners.