This demonstrates the inadequate in programs such as Medically Assisted Treatment; his Methadone isn't holding him as he inadvertently uses Fentanyl as well as Heroin
and he should be liaising with his doctor and getting on a much larger dose.
Buprenorphine could be a better treatment option to keep their opioid receptors occupied (as Bupe has an extremely high binding affinity) and defer withdrawal. I found this study after thinking about what to edit here.
Remember, most of us are a paycheck (or two) and/or a bereavement and/or a physical/mental illness away from homelessness.