My wife actually asked this of some professionals working in this space yesterday at a local awareness event (she works in community services, unrelated to drug policy). The answer (paraphrased) was it doesn't directly stop the poisonings. It's in the spirit of harm reduction to open up more support channels. One example given was about going to the hospital and honesty with health professionals. Currently there's disincentives for an addict to disclose their addiction due to legal actions that get triggered upon disclosure. Removing those legal triggers could (would?) allow for more supervision without legal consequence to hopefully reduce the overall harm. It gave us something to chat about.
I don't know if the federal government plays a role here, but the duty to report type laws for professionals are typically at a provincial level. That being said, as far as I know, they are fairly consistent across provinces.
One example provided, which I've not fact-checked and might be limited to BC, was that disclosing addiction during a hospital visit opens up a file with child welfare services.
