Oops! I've just read this "[The authors report] that grapefruit, grapefruit juice, and some other citrus fruit, including Seville oranges, limes and pomelos, contain a class of chemical called furanocoumarins. Furanocoumarins inhibit an enzyme, cytochrome P450 3A4, that is responsible for the inactivation of approximately half of all drugs" (
http://www.nhs.uk/news/2012/11November/Pages/Prescription-pills-and-grapefruit-a-deadly-mix.aspx). I spend a lot of time reading the information leaflets that come with my medications because of my allergies but don't remember reading anything about other citrus fruits. It's quite frightening, as I already have a list of things I have to be careful eating/must not eat, apart from all the things I am allergic to. Good job I don't eat a lot of marmalade.....