I feel like interventions are as much for the family as they are for the addict. It's a chance for the family to say, "We see a problem. We are complicit in the problem. We don't want to do this anymore."
Whether that has any effect on the addict? YMMV.
There were several "interventions" for my STBXAH trying to corral him into rehab. He wasn't ready and it started a pattern of roller coaster expectations and failures, and him lying about his "recovery" while he was just learning to drink more covertly. All of us friends and family at home were all over him looking for signs of real recovery. It got weird there for a long while.
Doing it ourselves was a mistake too. There was one in particular with me and his parents, where his dad wanted to control the whole outcome of the intervention. His idea was that if he could just "get" AH to "tell the truth" that everything would... I don't know what. But that's their pattern: FIL wants the truth, AH tells as much truth as won't upset the apple cart or endanger his enabler situation, and everything goes back to head-in-the-sand-normal.
It's exhausting.
Anyway, this particular time we confronted AH about his drinking, he denied he was drinking at all, and my FIL was like, "Okay then! Never mind!" I'm pretty sure he was drunk
AT THAT MOMENT.
I was gobsmacked.
What I'm getting at is that we have our patterns too, and it's difficult to operate outside of those patterns without outside help. Even then, whether the addict gets the message and turns it into lifetime recovery is another thing. I think it's better to measure our commitment to change, to being on the same page and not sabotaging ourselves or the addict, and our exhaustion with enabling the addiction when it comes to approaching intervention.
If I could do it all over, that's how I would approach it.