IANAV, but…
Has the vet actually examined the cat, or has this been an over-the-phone thing? Many years ago, I had a cat that had a thick coat and was prone to hairball-related constipation. One day we realized she hadn’t had a bm for a couple of days, so we gave her hairball medicine, with no results. We called the vet and he suggested a higher dosage. Still nothing, and she was starting to vomit, which we assumed to an attempt to clear out a hairball. Another call and he suggested a baby suppository or enema. We weren’t brave enough for an enema attempt, but we did do the suppository. The (hardwon) results were not impressive and about that time the cat decided to stop eating. It’s been a long time, and some of the details are hazy, but I know we did take her in to the vet at some point during the week or so that this was going on. He said he was able to feel an obstruction which he believed was a lodged hairball. (This was a rural office, and I don’t think they had an x-ray machine.) He gave her a laxative injection and had us take her home where we were to wait and see if it had an effect. Nope. We took her back to the vet, and he gave her an enema. While watching her, he kept exclaiming that she wasn’t straining, as would be expected if she was attempting to pass something. The following day he did surgery on her, and discovered, instead of a hairball, a tumor, noncancerous, fortunately. The tumor was either in or on her spleen, so that had to go as well. He told us he had never seen that condition in a cat. Later when we told another vet about it, he just looked at us like he didn’t think we really knew what we were talking about, but when we brought it up to our current vet some years after, his response was to the effect that it wasn’t common, but it did happen. (I’m guessing that in the past many cats would not have survived long enough to have the surgery done and the tumor discovered.) And yes, she did live, and spent several more years terrorizing us all and throwing up the occasional hairball.
Anyway, of course it isn’t always that complicated. More recently, we had a cat that had long hair and was prone to, well, see the above. When she did the no bowel movement or eating thing, we took her to the vet, she was given an x-ray, an enema, and a laxative shot, everything came out all right, no tumors or anything, end of story.
So these are my constipated cat stories. I guess the moral is that there needs to be an actual exam done so that a determination can be made as to whether this is simple constipation or some exotic condition that amazes the vet.
I love those Felix-the-Cat looks.