Eh, if he's using it's not hard to get a script. With the host of mental issues he is packing, decent insurance, and living around a large metropolitan area, doctor shopping for whatever you want is not hard, even with recent crackdowns.
If Wu were hitting a pipe (other than Frank's), or using any other street drug outside of Marijuana I would be surprised. Someone like frank has too much to lose to be around that when there are legal alternatives.
Plus if he were using that sort of drug, he would be screeching on Twitter about how everything needs to be Amsterdam tier legal, and virtue signaling for druggies... or paradoxically taking a hardliners opposite stance. I see neither, and if Wu is an abuser, it is with a prescription drug as it would bruise his ego to be addicted to a street drug.