Step 1 of 5 Food poisoning is an illness caused by eating contaminated food. It's not usually serious and most people get better within a few days without treatment. The symptoms of food poisoning usually begin within one to two days after eating contaminated food, although they may start at any point between a few hours and several weeks later. For more details and advice on when to see your GP please check NHS Choices. Where did you purchase the food? Enter the name and address of the UK business and select from the dropdown list.