what are the foods that are considered drugs?

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I have a cousin who takes coffee and cola for his study and became very successful. He was awarded the best student in journalism and work for a number of years. After some years he had some mental problem and the doctor said it was as a result of the cola and coffee that he takes. They have to chain his legs to make him stationery or he says he will kill some personalities for they are the cause of his bad conditions. when he is in that bad mood he can speak many languages that people think he has not learnt. when my dad is hungry he take cola and he drinks more water and regains his strength according to him. I don't know why the cola and coffee can contribute to somebody's madness? are they drugs?