Dirtebiker is correct, true opioid addicts are not really influenced by mortality concerns and nor do they use with some sort of moderation where they make value judgements about how much to use.I say only for trained professionals and LEO's. If anyone can have it users will just use more.
They use as much as they think they need to feel right, and will continue chasing that feeling until their lungs stop.
I would be very surprised if the presence of narcan has any real influence on use patterns. Usually the limiter is money/access.
Having stuff around for an addict to steal is far more enabling than the presence of Narcan.