Mainstreaming Addiction Treatment Act of 2021 This bill removes the requirement that a health care practitioner apply for a separate waiver through the Drug Enforcement Administration (DEA) to dispense certain narcotic drugs (e.g., buprenorphine) for maintenance or detoxification treatment (i.e., substance use disorder treatment). Further, a community health aide or community health practitioner may dispense certain narcotic drugs for maintenance or detoxification treatment without registering with the DEA if the drug is prescribed by a health care practitioner through telemedicine. It preempts state laws related to licensure for this activity. The bill also 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.