This is a grisly subject and so a film dealing with will be grisly. Not for Christmas fun, but essential viewing for anyone who may know someone with addiction and wish to understand them.
This is not the place to be judgemental, as we see this could easily happen (maybe is happening) to any one of us. We're shown pleasant characters who have a demon, even when we see this demon we see it's engrained further into these people than we imagined.
The 'silent protagonist' as a metaphor for the silent, attractive, feeling of 'right' that is addiction is genius and powerfully portrayed.
An uncomfortable viewing, but essential nonethless (how many continue to watch Seaspiracy etc!) It's something about which we all benefit from being better informed.