Anya was taking some medicine that upset her stomach. Later that day, when she drank orange juice, she became violently ill. Since then, Anya feels sick to her stomach if she even thinks about orange juice. One day when Anya is out with friends, the waitress puts a glass of grapefruit juice near her. Anya immediately feels sick to her stomach. Anya's nausea in response to the grapefruit juice is most likely the result of .