I may be wrong, but I do not think ibuprofen is effective against inflammation of the CNS - probably because it does not cross the blood-brain barrier (I’m only guessing that bit).
So I don’t think there would be any virtue in taking it long-term at low dose as a precautionary measure against MS, because it doesn’t address the same kind of inflammation.
Having said that, I take quite a lot of ibuprofen and paracetamol anyway, but for pain relief, not as an attempt to stem MS. It just so happens that most of my pain seems to be muskulo-skeletal rather than neuropathic, so I get more relief from conventional painkillers.
So in that sense, I do not think there is a danger. I accept it’s not ideal I’m on so many painkillers, but it’s not ideal to live with untreated pain, either, so my GP has reassured me there is little danger to an otherwise healthy (haha - barring the MS) person, from long-term use as prescribed. Millions of people with chronic pain have to do this, and it’s not a problem if done under medical supervision - all this: “Do not take for longer than four days” on packs you buy over the counter are for the ordinary Joe with a sore throat or headache, NOT for those of us with chronic illness who are getting it on prescription.
I don’t think there is any danger (or not much) from taking them regularly for pain - just no advantage if you’re not in pain, or if your pain only responds to neuropathic painkillers. I certainly don’t think they will do anything to prevent Uhthoff’s phenomenon. I do think paracetamol is beneficial if a pseudo-exacerbation is caused by a feverish infection, such as a fluey cold, as anything that helps control the fever should reduce any symptom flare-up. However, I don’t think paracetamol taken routinely will do anything special when you’re not ill (except for the MS).