Strengthening Partnerships to Prevent Opioid Abuse Act of 2018 This bill requires the Centers for Medicare & Medicaid Services (CMS) to establish a secure online portal to allow: (1) data sharing among the CMS, Medicare prescription drug benefit plans, and Medicare Advantage (MA) plans; and (2) referrals by such plans of suspicious activities related to fraud, waste, or abuse in order to initiate or assist investigations by contracted entities under the Medicare Integrity Program. The CMS must disseminate and report certain collected information to such plans, including information regarding providers that were referred through the portal and trends in identifying suspicious activity. Additionally, for plan years beginning on or after January 1, 2021, MA organizations must submit information to the CMS regarding credible evidence of suspected fraud or other actions taken by MA plans regarding inappropriate prescribing of opioids (as determined by the CMS).