In the US, advertisers must get ads cleared by the national networks (NBC, CBS,ABC,FOX) before they can be aired on those networks. The challange EVERY claim that’s made and will ask for the research or legal substantiation. Local networks can ask to clear a spot, but it’s rare because they need the money and are not as concerned with the national reputation. Cable networks will run ANYTHING and wont ask for any substantiation.
That’s the broad answer. There are then separate rules down to day-part as to what can/can’t be aired by the National networks.