Recently I got an autism diagnosis and got Fluoxetine prescribed.
Getting on it was a living hell. I was extremely tired, could barely walk the stairs, my body was in pain, I could not drink coffee anymore, just to mention some effects.
I endured, and I am much less edgy, more social, less depressed, and less anxious
The only remaining side effect is that alcohol effect is nearly 2x as strong as it used to be. And it already was strong for me. So one glass is the max for me... tho I had a similar effect from Citalopram.
My point being, for me Prozac works with making my autism's effects less severe allowing me to function better in our NT society. According to my psychiatrist (specialised in autism) I was not the first whom she described [Edit: prescribed] that ie. I wasn't an isolated case.
IBS has many causes one main of is people having an autoimmune disease due to the bodily production of anti-vinculin from molecular mimicry of the toxin causing food poisoning anti-cdtb.
The remaining causes are related to MAST cell destabilization, SIBO, etc. Anxiety is thought to play a role in symptom management in the same way having being anxious about a broken foot will make you foot hurt more.
I got put on SSRIs because it was the only thing that helped my IBS after getting some kind of GI infection while traveling in Europe.