The Garcia effect was discovered by American psychologist John Garcia while conducting radiation experiments with rats. It was found that rats would develop an aversion to the smell or taste of a novel type of food when the initial exposure to the food was followed by a toxic reaction. The conditioning occurs even if the toxic reaction is not evoked until several hours later.
The same effect can be observed in humans, and is a common problem experienced by people undergoing chemotherapy.
Source:
Roeckelein, J. E. (1998), “Dictionary of Theories, Laws, and Concepts in Psychology