How old is your son?
I have a problem with coke and im lapsing every 3 to 4 weeks.
When you are coming down off coke it can make you suicidal and really really down, this is because you have used all your dopamine up from your brain, when on a high. And when the coke wears off u have none left and suicidal thoughts kick in. Dopamine is what makes us think happy thoughts and balanced.
Your son has to want to quit if you want him to stop. Its hard but there are a lot of ways to stop. One is no drinking alcohol as this is a main trigger for coke. And another is to delete all friends numbers and coke dealers who take coke.
There are so many people on coke now. Its in every pub, girls are as bad as lads on it aswell.
Its a nasty repetative circle being on coke.
Id just make your son aware of how bad it is, until he wants to stop himself.