Opioid Advocacy Transparency Act of 2018 This bill expands reporting requirements related to the ownership and investment interests of certain patient-advocacy organizations. Under current law, a manufacturer of drugs, devices, or medical supplies that are covered under Medicaid or Medicare must regularly report on any payment or transfer of value by the manufacturer to a "covered recipient," defined as either a physician who is not an employee of the manufacturer or a teaching hospital. The bill expands the definition of "covered recipient," for purposes of this requirement, to also include patient-advocacy organizations that advocate on issues related to opioids. Furthermore, with respect to transfers of value to such organizations, the bill subjects not only manufacturers but also pharmaceutical trade associations to the reporting requirement.