Mainstreaming Addiction Treatment Act of 2019 This bill removes the requirement that a health care practitioner apply for a separate waiver through the Drug Enforcement Administration to dispense certain narcotic drugs (e.g., buprenorphine) for maintenance or detoxification treatment (i.e., substance use disorder treatment). Further, the bill directs the Substance Abuse and Mental Health Services Administration to conduct a national campaign to educate health care practitioners and encourage them to integrate substance use disorder treatment into their practices.