A problem LAR programs have had since the start is that although methadone is less attractive as a drug than heroin, it's still attractive, and basically the only way to figure out how much a heroin addict needs is to ask them. Leading to users asking for extra, selling the excess (to users who were not in the LAR program) and buying other drugs with the profits. For some years, more people died from methadone overdose in Norway than heroin.

Sure, you could demand injection on site to reduce this problem. But that just makes the program less appealing. You could also just hand out the users' drug of choice directly (heroin) rather than the less harmful substitute, but at some point that starts counting as physician-assisted suicide, really.