Hello, My Son Has Pseudocholinesterase And One Doctor Told Me

Hello, my son has pseudocholinesterase and one doctor told me he should not take cocaine or he could die. He`s only 9 years old but I'm wondering what other drugs or if alcohol could harm him. I'm concern that in his adolescent years he might want to try some things and I want to inform him while he's young. Can pot, alcohol or other drugs harm him?