Yes! ofcourse the film is really supposed for many to be a spoiler.
I, instead, appreciate he asked such a simple question that he couldn't get some thing a point.
Which I believe, for sure, many of us have drawn various points out of the story. and I think can be discussed at some extent. so I think rather harassing others there should be clear understanding. And here is what I understand.
there is a very bit difference in the novel and the film story. And that exactly is the very last dialog delivered by the Andrew(Teddy) in the film
"what would be the worse? To live as a monster..... or to die as a good man..." it actually shows not only to the audience but as well to the Dr. Sheehan (Chuck) that it reflects not the sign of him to be still a mad. It does show that the treatment was successful. That alerted Dr. Sheehan and upon calling him Teddy, he didn't get a response back from him.
you should try to get the point when Dr. Sheehan called him as Teddy after the above dialog, He didn't reacted or responded back. In a good directed film these indications are to show the reality behind the scene. but I know it's hard for many of the audience to get these points.
The difference from the novel is always needed to put in a Film to make it just simple in the audience's mind not to get disturbed because the Andrew(Teddy) was the lead role and it would have been really disturbing when some lead role got an end like that e.g. being killed, murdered, or being still crazy.. etc..
The films are meant to entertain people so it's good to change the story at a level that audience could easily accept that.
Finally the Film was really a good. you can say it perfect suspense, if you are not familiar with the novel.
There would be rare individuals who could say that they got the idea what would be there at the end of the film.