An observational proof of concept method comparison study. Comparing Liquid Chromatography -Mass Spectroscopy to a new Quantitative Lateral Flow Immunoassay with an Optical Reader.

CARI Health, Inc.'s long-term goal is to address the problem of high dropout rates of patients receiving medication for opioid use disorder (MOUD; e.g., methadone) treatments, which has increased with the prevalence of fentanyl use, with an innovative point-of-care (PoC) device to enable science-based personalized dosing for patients receiving methadone treatment for opioid use disorder (OUD). The proposed solution consists of a customized analysis device that incorporates proprietary methadone detection technology for quickly measuring methadone and metabolite levels in the blood and calculating the methadone/metabolite ratio (MMR).

To accomplish this long-term goal, the investigators aim to first quantitatively measure methadone doses taken and ethylidene-dimethyl-diphenyl pyrrolidine (EDDP) detection using lateral flow assays. At this stage, the investigators are not testing a device. They are first assessing whether methadone metabolism can be evaluated using lateral flow assays, which are simple paper-based diagnostic strips. The tests work similarly to a home pregnancy test, where a sample (like blood, urine, or saliva) flows along a test strip and interacts with antibodies or other molecules that capture the target substance. No clinical decisions will be made, no treatment will be applied, and no dosing will be changed based on the results learned in this study.

Inclusion Criteria:

Age 18-70. A prescription for methadone at a dose of 10mg or more for at least 7 days. Participants may be taking the methadone to treat an OUD or for pain. Taking methadone as prescribed during the last 4 days before consent to participate in the study.

Has been prescribed at least 1 day of take-home doses.

Exclusion criteria for methadone group includes:

Age <18 or >70. A condition preventing or complicating blood collection. Conditions may include dermatological (skin) condition, bleeding diathesis, immunodeficiency, recent blood donation, anemia, end stage renal disease, liver cirrhosis, cancer, congestive heart failure, bleeding diathesis, tuberculosis (TB), active severe depression (e.g., suicidal ideation), or mania symptoms.

Tattoo or piercing close to sampling area. Under a conservatorship.

Patients with pain or opioid use disorder that are taking methadone daily.