Responses
He is suffering them. That's why his toilet got clugged, he was throwing up.
Also in that same scene he thinks about drugs. Maybe that's why he also lose weight (as said by Conor).
He's handling by himself in secret, but I do too think he's not as bad as he should for someone abusing that hard in heroin and stuff.
I was wondering about that too, but it turns out he is suffering them but he's dealing with it quietly. He really started to feel it during jail.
It is strange that Simon dosen't show an signs of withdrawal symptoms or did I just miss that part !!!