Napoléon was chronically ill the last five years of his life. The poisoning theory explains this by him falling victim to repeated poisonings. During five years he suffered sub-lethal arsenic poisonings. The last six weeks the arsenic was partially replaced by antimony. Eventually he was given calomel after having been served a drink containing bitter almonds. It was this combination which eventually took his life.
A common misconception in this case is that he would have been poisoned by “jailors”. Any literal such did not exist. His last years Napoléon in a jerry-built mansion. There his own food and drink was handled by six male followers. Therefore, the person poisoning him must have been one of them.