For decades the American system asked homeless people with mental illness and addiction to earn housing by getting sober first. In the early 1990s psychologist Sam Tsemberis inverted the sequence, and Canada's randomized At Home/Chez Soi trial later showed large gains in housing stability. The verdict is measured: proven for what it promises, but necessary, not sufficient.
Evidence for housing stability is strong, but gains in substance use and psychiatric symptoms are modest and mixed. Disputes include whether to judge high-fidelity programs or what is actually funded, whether it scales where housing is scarce, and how it fares in the overdose era.