In the Marvel universe, the alien symbiote Venom has a weakness to loud noises and fire. Additionally, the symbiote needs certain chemicals to stay healthy and bonded to its human host.

It was established in the comics that two key ingredients Venom craves are phenethylamine and theobromine. Phenethylamine is a natural chemical found in the human brain that induces feelings of love. Theobromine is an alkaloid that can act as a stimulant.

Chocolate happens to be a rich source of both phenethylamine and theobromine. That’s why when Venom’s host experiences strong emotions like love or anger, Venom manifests an urge to binge on chocolate. It provides the symbiote with chemicals it can’t easily produce itself.

So in essence, Venom is addicted to the phenethylamine rush and stimulated by the theobromine when it eats copious amounts of chocolate. It helps satiate the alien symbiote’s appetite when bonded to a human.