Given the circumstances described—an addict who has previously attempted outpatient treatment unsuccessfully, lacks stable housing and employment, and has few social supports—the most appropriate treatment option would be:
Residential treatment.
Residential treatment provides a structured environment where the individual can focus on recovery while receiving support in a communal living setting, which is beneficial for someone without stable housing or a strong support system. It offers comprehensive therapeutic services and a supportive community, which can be crucial for someone with a history of unsuccessful outpatient treatment.