It's not the first that Pretty Little Liars actress, Troian Bellisario has told us of a "secret" about Spencer that will be revealed in the second half of season 4, as Troian tells E! Online that said secret will "really, really affect [Spencer's] relationship[s]".
"What you're going to see in 4b is a very, very interesting secret that you never knew, that we never talked about with Spencer." the actress explains, "It really, really affects her relationship with Toby and with the girls, and it reveals a lot about why she wasn't passed out with the other girls the night that Alison died. I'm so excited we're finally getting into that, because I've been waiting for seasons to get into that."
It's been hinted that we'll learn about Spencer dipping into drugs/pills, at some point during season 4. Could this spoiler be part of a larger problem Spencer has been dealing with since day 1?