Opioid Treatment Access Act of 2022 This bill expands access to substance use disorder treatment by modifying the regulation of opioid treatment programs and narcotic drugs used for treatment, including with respect to a patient's unsupervised use of such drugs. Specifically, the Department of Health and Human Services (HHS) must issue regulations to further increase patients' access to unsupervised use or handling of drugs for treatment. The Substance Abuse and Mental Health Services Administration (SAMHSA) must study the effects of these revisions, and HHS must, as appropriate, promulgate additional regulations based on the study's findings. SAMHSA must also study the impact of certain exemptions from certification requirements for opioid treatment programs that were granted as part of COVID-19 response efforts, including any additional costs or savings that resulted from the exemptions. The bill also (1) allows specified types of health care providers to prescribe (subject to certain requirements) methadone that is dispensed through pharmacies for a patient's unsupervised use, and (2) provides statutory authority for a regulation that allows registered opioid treatment programs to operate mobile medication units without separately registering the unit.