The Garcia Effect (aka, conditioned taste aversion) is an aversion or distaste for a particular taste or smell that was associated with a negative reaction (such as nausea or vomiting).
This effect was discovered by John Garcia while he was studying effects of radiation on mice. He noticed that rats would avoid a new food when it was initially presented around the time of radiation exposure, which causes nausea and a general feeling of sickness. The Garcia effect occurs in patients undergoing treatment for cancer who are exposed to radiation as treatment. It can also happen in humans when a bad reaction occurs as a result of ingesting a particular food or drink, either from food poisoning or overindulgence.