I'm on multiple medications and have experienced developing a tolerance to the meds I'm on. Sometimes I've had to go to a higher dose or change to a different medication.I have been taking Clonidine for sleep. Been on it for a few years now.
Hydroxyzine has a brand name of Vistaril. It is used frequently as a sedative. It is one of those drugs where you can scream your head off for a procedure (dislocations, setting bones, stitches) but not remember a single thing. I have been taking it for years for its antihistamine properties.
Both Clonidine and Hydroxyzine can be a pain to taper down or completely stop using it. I would think this is something they discuss with Abie's doctor, if either are still working or do they need to adjust the dose. Developing a tolerance to a drug is very common, and require higher doses.
I would hope that Abbie's Doctor is on top of it. Altho, given A&P's behaviors and dispositions, it wouldn't surprise me if the Dr has suggested taking Abbie off certain meds or lowering the doses but Tinkerhog and Ass-hat wouldn't stand for it.
Asa has said in the past that he doesn't want Abbie to be a medicated doped-up zombie. That's why he dragged his feet for a long time when it was clear that Abbie's current dosages were no longer working for her (due to the tolerance as you mentioned) and Asa was very resistant to the possibility of increasing the meds. While I believe Asa does feel that way for the most part, I sort of wonder if there's another side of him that is glad the meds calm her down and wouldn't be opposed to increasing them (during the times when she's super 'hyped', or having non-stop tantrums all day)
This is just purely my speculation, of course.