Earl Grey and Bergamot oil the toxicology adverse health warning

Earl Grey tea is a blended tea with a distinctive flavour and aroma derived from the addition of bergamot orange oil.
Earl grey was traditionally a black tea, however today the term is also applied to green teas, including white tea and oolong, and tisanes, such as rooibos, that contain oil of bergamot.

Toxicology warning of Earl Grey Teas

In one study, oil of bergamot the distinctive flavour of Earl Grey has been linked to certain phototoxic effects (due to the chemical bergaptene) and blocking the absorption of potassium in the intestines.
Finsterer J (2002). "Earl Grey tea intoxication". Lancet 359 (9316): 1484. doi:10.1016/S0140-6736(02)08436-2
Bergamot is also a source of bergamottin which, along with the chemically related compound 6’,7’-dihydroxybergamottin, is believed to be responsible for the grapefruit juice effect in which the consumption of the juice affects the metabolism of a variety of pharmaceutical drugs.
David G. Bailey, J. Malcolm, O. Arnold, J. David Spence (1998). "Grapefruit juice-drug interactions". Br J Clin Pharmacol 46

History of Earl Grey
The Earl Grey blend is named after the 2nd Earl Grey, British Prime Minister in the 1830s, who reputedly received a gift, probably a diplomatic perquisite, of tea flavoured with bergamot oil, taken from bergamot, a citrus fruit typical of southern Italy.
The legend usually involves a grateful Chinese mandarin whose son was rescued from drowning by one of Lord Grey's men, although this blend of tea was first made from fermented black Indian and Ceylon teas. As green tea is much more popular in China than black tea, it seems somewhat unlikely that they would have had a recipe for what we now call Earl Grey to bestow on visitors, though over the years many other varieties of tea have been used. In addition, Lord Grey never set foot in China. Another version of the legend has the son of an Indian raja being rescued from a tiger by one of Grey's servants.
Jacksons of Piccadilly claim that it was they who originated Earl Grey's Tea, Lord Grey having given the recipe to Robert Jackson & Co. partner George Charlton in 1830, according to Jacksons the original recipe has been in constant production and has never left their hands. Theirs has been based on China tea since the beginning.
Because of Earl Grey's aroma and Twining's distinctive packaging in England with Charles Grey, 2nd Earl Grey, the tea is sometimes called "Old Stinky".