In the play Hamlet, how does Ophelia get used or looked down upon by other characters?
Interesting question. Ophelia is, indeed, used or perhaps mistreated by some characters in Shakespeare's Hamlet. Let's begin with her own family. Laertes does love his sister, as evidenced both in the beginning as he is leaving for school and in the end when he jumps into her grave, stricken with grief. But he does lecture her in a way which leads her to remind him to do as he says for himself, as well. Clearly this has been an issue in the past; but rather than abuse this is probably classified more as Laertes simply being a big brother. Her father, on the other hand, could be considered abusive. He forces her to cut off a relationship with someone she clearly loves. He sends her out as "bait" to catch the mad Hamlet (he says he will "release her" to him, a term used for animals but not generally for humans). He is willing to mistreat his own daughter to keep or enhance his own power and position.
Claudius, by his acceptance of her use as bait to trap Hamlet, is tacitly approving of Polonius's abuse of Ophelia. Gertrude, on the other hand, does seem to care for Ophelia, as she hopes Hamlet's "madness" is caused by love for her. Of course, that could also be because she does not want to admit that she may have something to do with it. She also wants to keep her out of his presence once Ophelia has gone mad, as it makes her uncomfortable--a fairly hard-hearted sentiment for someone she once hoped her son loved.
Finally, no one was watching out for Ophelia's best interests once she went mad. She was isolated from everyone and "put away" as soon as they could reasonably get her out of their presence. The fact that she made it to a brook and was able to drown herself is appalling. Someone was able to relate what happened to her, which means either someone was actually there or was watching from a distance. In either case, letting her drown was the final abuse.