Yeah, I find it interesting that all she offers Rich is weed. No coke, meth, morphine etc. While what she's been selling the jocks (Birth Control pills or sugar masquerading as them) is also kind of weak sauce.
In terms of addiction, I think both Tommy and Riona are in deeper than Quinn. So if DPC has anyone ODing in the game (and I am not saying there will be any at all), it'll be between those two methinks.
Maybe, but I think Quinn is pretty hooked. She is clearly using some fairly hard stuff, harder than anything we've seen Riona use. Based on the scene at the start of Episode 2, she had to talk Tommy into using whatever they injected. She can say it isn't addictive, but I wouldn't trust her word on that when she was sober, much less when she was high!
On top of that, Quinn's actions are, IMHO, the most unhinged of the known drug users. Sure, Tommy is a complete jackass freeloading off others, but that feels more like entitlement than addiction. And even he realized her plan to ditch the DIKs was doomed to failure. Riona has been calling out Quinn's idiocy since we first learned there was a problem.
Quinn, meanwhile, thought she could solve the problem of telling Tommy by avoiding him. She tried to sell drugs to
Tybalt, and was only saved from her own stupidity by the fact Tybalt pawned her off on Rich. She is, to all appearances, trying to bring Ashley and Maya into her prostitution ring, and based on how she handled Mona's defection, doesn't have much of a plan if they spill the beans.
People will often do irrational things, so it could just be that Quinn is headstrong and unable to face consequences. But that doesn't mean the drugs aren't playing a part, too. It certainly wouldn't surprise me to learn the root of her shortage is that Quinn has been using more and more drugs to cope with all the problems coming up.
The drug arc is only just getting started, so we'll see where it goes. But I don't think it's coincidence that Quinn is at its center.