Is he in danger, should I tell someone?

[Hello]

Me and my ex broke up several months ago and agreed on no contact we haven't spoken since. Before today he's never drunk a drop alcohol but just this afternoon on his twitter account he said he decided to start drinking to drown his sorrows, so far he's had 3 bottles of cider and he's tweeting a bit drunkenly. I know drinkings not a bad thing but the thing is he's very depressed, he's a self-harmer and he has 50 boxes of paracetamol stashed in his room for when he wants to take an overdose, and he's refused to get help for any of this. The only reason he's drinking is because he thinks it will take away his unhappy life, he's only 18, is he a lot more likely to do something stupid now he's drunk? I have his mum's number, I could tell her to keep an eye on him but I don't know if I'm over-reacting? How dangerous is it that he's got all these pills and self-harms, and now is getting drunk?