IDK if it ever worsened my stimming but I've had MAJOR difficulties from taking most antihistamines and even nasal allergy sprays(corticosteroids) that weren't even supposed to be absorbed into the bloodstream.
I'm very sensitive to them for whatever reason, I was on Claritin for about a year before I realized what a miserable person it was making me. I did not have any desire to speak to anyone, I was very angry all the time, I actually got diagnosed with GAD because I was having anxiety attacks and daily anxiety about pretty much everything.
I was having meltdowns, shutdowns, walked out of a job...it honestly made me seem very mentally ill. I guess it just brought the AS traits out of me like nothing ever has, I have all of those problems in varying degrees without the drugs but it's something that I can normally work around, not be constantly overwhelmed by, and I am a reasonably friendly person in my natural state. I didn't even pretend to be friendly when I was taking that stuff, I can't even believe how much my behavior changed. As soon as I stopped taking the stuff I realized what a complete jackass I had been.
It's crazy because they really don't affect most people that way. I've seen A LOT of stories on patient/drug review sites like mine but many of those people exaggerate (I think if Claritin makes you have, "very real fantasies about killing small children" then you have some serious issues to deal with or you're just being a douchebag) and are on about 13 different medications so you don't really know what to believe. In reality, they do worsen depression and anxiety for some people but it isn't extremely common.