Drugs and Alcohol
One longing for the night (214)
Laura can't wait for her second taste of goblin fruit. She's like an addict: she can't focus on anything but where her next fix is going to come from.
Then sat up in a passionate yearning, And gnashed her teeth for baulked desire, and wept As if her heart would break. (266-268)
Laura seems to be showing signs of physical addiction. We see that she is actually in pain here.
Laura kept watch in vain In sullen silence of exceeding pain. (270-271)
Laura is secretive about her addiction, too. She doesn't even tell her sister what's happening.
She dreamed of melons as a traveler sees False waves in desert drouth With shade of leaf-crowned trees, And burns the thirstier in the sandful breeze. (289-292)
Laura is even hallucinating about the goblin fruit, but it's all a dream. When she wakes up, her withdrawal symptoms are even worse.
She no more swept the house, Tended the fowl or cows, Fetched honey, kneaded cakes of wheat, Brought water from the brook (293-296)
Laura's addiction makes her change her normal routine. She's no longer capable of performing her usual chores.
But sat down listless in the chimney-nook And would not eat. (297-298)
Laura's whole personality changes after becoming addicted to the goblin fruit. She becomes depressed and "listless," and loses her appetite.