if you go from being someone who half ass trains or doesn't even train at all to have your ass kicked by the best trainers and nutritionists money can buy, you are going to make dramatic changes.
i don't know whether they used or not (although you can tell butler did in 300, he's even got gyno) but it is not necessary to use to get into that kind of condition.
think about it- these guys are living the good life, most likely exercising somewhat, but with few exceptions not at the level that will give you that kind of build.
so, four months out from the film the studio provides them with a top level trainer who works with them for every rep of every exercise and a nutritionist who has meals ready and prepared for them every day. total convenience for the actor, who just has to follow direction. their paychecks are motivation to get in shape.
what i'm trying to say is that you would be surprised what you can do with those sort of resources and motivation. do some of them use regardless? probably. but it is possible to be 5'10", 170 in very good shape without anabolics... and you'll look 185 on screen.
also- these guys are not that big, with the exception of the thor kid. i watched his trainer slap 20 pounds of muscle on him after filming troy. he probably used and he looked damn big too.
anyways he is the exception. these guys are not that packed with muscle. you don't see them with 30 inch thighs and thick backs- they have arms, a chest, and abs. these muscle groups aren't the ones that hold all the weight.