Conversation so far:
Did John Harvey Kellogg support drinking alcohol?
he felt that alcohol was a poison.
Why was he against alcohol?
Kellogg noticed deleterious effects that alcohol had on both the brain, the digestive system, and the liver, among other organs.
What other beverages was he against?
CANNOTANSWER.
How did he feel about coffee and tea hot chocolate?
Kellogg also opposed tea and coffee due to the caffeine content.

Question: What did he feel was bad about using caffeine?
Self-contained rewrite: What did John Harvey Kellogg feel was bad about using caffeine?