During an interview a 2007 episode of Late Night with Conan O'Brien, actor B.J. Novak drew attention to the fact that American market Cadbury Creme Eggs had decreased in size, despite the official Cadbury website stating otherwise. American Creme Eggs at the time weighed 34 g and contained 150 calories. Before 2006, the eggs marketed by Hershey were identical to the UK version, weighing 39 g and containing 170 calories.

Is it true that did cadburys cream eggs used to be bigger?
yes