Hi Enlightened,
I can't give any general responses, but perhaps my experience with my n-mom will be helpful in some way. Just keep in mind that all Ns are different, of course

My mother was put on anti-depressants about seventeen years ago - if I recall correctly, she started out on Prozac. It did help a bit, in that she was a bit slower to anger and had brief moments where she recognized our existence (my brother and I). On the other hand, she felt that her doctor had fooled her by diagnosing her with depression and putting her on a medication that was in fact "for crazy people". So my mom took her dosages into her own hands, going through periods without taking Prozac at all - which was sheer hell on earth considering the withdrawal - and then after months of us desperately trying to convince her to go back on, would realize that maybe, after all, the Prozac did help, so would start taking it again. Her doctor figured out that she'd gone off it herself even though she didn't tell her, thank goodness, and the prescription was continued with strict instructions to follow it to the letter and consult the doctor before messing around with anything.
My mother went through another one of the cycles anyway, and found a new tactic: she went to a different doctor, complained that her old one wasn't trustworthy etc. - the usual N backstabbing - and was put on a different antidepressant, with the same results.
She's been on four or five different medications over the years, all with the same effect: an initial "top of the world" period where she's heaven on earth to everyone except her own family (although almost livable), followed by her paranoid self thinking that the doctor has tricked her into taking "crazy people pills", after which she goes off of them without consulting her doctor. Her favorite thing to do is read up on every possible use of the medication she's on, find something like "may be prescribed for [whichever serious mental disorder]" and then claim that she can't possibly take it because she doesn't have THAT.
Her going off the medication without being properly overseen then causes withdrawal, which only serves to aggravate her narcissism. She'll bask in the attention of everyone trying to convince her to go back on the medication, sucking the entire family and all her friends for all the sympathy and worry they're worth, finally agreeing - when everyone is purely exhausted from supporting her - to go back on. She levels out to a tolerable state of existence (I mean tolerable from the point of view of a narcissist's child, so basically just a nicer level of hell), and convinces her doctor to prescribe her a different one because she "doesn't like the side effects of the one she's taking". The doctor, having no idea that my mom has gone cold turkey for a period of time, acquiesces and the cycle begins once more.
(Just a side note, I no longer allow her to ask me for advice about her mental state. Likewise she isn't allowed to give me "advice" about mine

I also live very far away and so never have to deal with it directly. But according the few normal people in my family who still have to be around her, nothing's really changed.)
As your mom's older, perhaps the initial golden period would last? It all depends on how paranoid she is about being seen as crazy, I think.