It's a common claim in Quebec that McDonald's put anti-emetics in the food. I think I heard four times over the last week, alone.
It's not uncommon for people to go to McDonald's when they're drunk because it apparently helps prevent them from vomiting. A lot of people attribute this to McDonald's putting anti-vomit "stuff" in their food.
The nature of the anti-vomit ingredients varies a lot, such as vitamin E but the claim is always that McDonald's food makes you less prone to throw up and that's because it has anti-vomit in it.