Inclusion Criteria:  must self-report past 5-year experience taking opioid and sedative drugs (for therapeutic or non-therapeutic reasons), but not necessarily at the same time, and may have current mild- or moderate-severity Opioid Use Disorder or current mild- or moderate-severity Sedative Use Disorder; must not be seeking treatment for their substance use problems; must be in current good overall health  Exclusion Criteria:  meet DSM-5 criteria for current psychosis, bipolar disorder, or severe depression (i.e. severe psychiatric disorder); meet DSM-5 criteria for severe substance use disorder for any substance (e.g. Sedative, Opioid, Alcohol); past-month benzodiazepine or opioid prescription (which would suggest daily use, tolerance, or withdrawal upon cessation); report of past-year any-drug overdose or suicide attempt/ideation; exhibit cognitive impairment (IQ < 80 on the Shipley Institute of Living Scale); neurological, cardiovascular, pulmonary, or systemic diseases (see specific exclusionary conditions under Protection of Human Subjects); body mass index > 32 kg/m2; females who are pregnant (urine), lactating or heterosexually active (self-report) and not using medically approved birth control; treatment with methadone, buprenorphine or naltrexone; past 30-day use of contraindicated medications; alcohol-positive breath sample (>.02% breath alcohol concentration); urine sample positive for methadone, cocaine, amphetamines, or barbiturates (<300 ng/ml)