I was told they can be prescribed (at the dose I was given possibly) a maximum of 3 times per year, due to their strength. The courses should also never last longer then 3-5 days at a high dosage (500MG) due to side effects such as heart palpatations, thinning skin, inability to sleep and other very nasty effects through repeated use.
They are intended to kickstart your body into regenerating your nerve pathways and reduce the swelling within your brainstem/spinal cord, but it’s not a guaranteed fix. They won’t nessecarily undo all your problems because it’s impossible to know until you try if the nerve pathways can be repaired by your body and even if they did before, sooner or later your body will run out of alternative paths.
I only took them once and thankfully they had a good effect on me, clearing up my vision, increasing the strength of my legs a little and regaining all of my dexterity and speech. I did notice after a few days my heart was racing sometimes though, obviously a side effect. It stopped happening a few days after the course ended.
I’m afraid I can’t tell you if your body ever gets used to them but you certainly shouldn’t be using them often enough for that to happen, you may aswell try assuming your neurologist agrees. You’ll feel a difference with 2 weeks if they have an effect, sometimes even sooner while you’re still on the tablets.