yeah. pretty deus ex machina'd the drugs thing. Perhaps if Tamayo's Resentment towards Muzan was honed on, such as creating a scene where she says "it's not enough... That demon needs to suffer more!" with Tamayo entity saying "You didn't think i'd just let you go with that much right? I tried all sorts of things just so I could drag you down to hell!" then it'd feel less of a plot convenience. Granted these statements are pretty out of character for her.
On another note: Nezuko getting her memories back! What's going to happen now? Honestly though I have a feeling it'll be along the lines of her rejecting her humanity so that she can protect her brother. Going further beyond, once Muzan dies to dawn, Nezuko, having remained a demon, will also slowly disappear because the demon origin is dead. A heartbreaking goodbye between brother and sister, or perhaps Tanjirou himself received fatal wounds, so they go to the afterlife together. Regardless, the ending will be completely bittersweet. That's my take on the final arc. Feel free to berate me because I definitely with 100% certainty spoiled the ending. You're welcome. (please don't im sensitive im sorry. I just wanted to share my opinions on a forum(?).)