As I've written in other posts, my fissure which has been here a while (too long!) and has gotten worse of late. i've relied on movicol pretty much every day since January although I had hopes of cutting my dose down when I felt I might be healing.
I'm just trying to stick to one a day right now (with lots of fruit and veg and fybogel once a day too) but BMs are still v difficult. I'm not sure if its spasming or the pain but I feel sort of constipated when I do go and BMs never quite feel 'finished'. Constipation was never a problem for me in the past and as I've said I've had lots of fibre in my diet (if anything more than I used to have) and have been drinking lots of water.
I wondered if anyone knows if its possible to become immune to the effects of movicol? Or that this is just a sign that the fissure has got worse?

It sounds like it's a spasm. Like you, I never had constipation until I got the fissure! And I believe it isn't actually constipation, just the muscle going into lockdown. Nothing can get past if it's so tight.
Having said that, I think the effects of any medicines lessen with overuse.
Could you try using something different, like MOM, or flaxoil, so you can alternate?

same thing happened to me Layla. I rarely got constipation but when I got my fissure, I couldn't go. The PA in my CRS's office said it was the spasms. As Val said the muscle goes into lock down.

Thank you for your replies guys. I think you're right it must be spasms. I think I'll just up my dose of movicol to be on the safe side. Can't hurt I guess.

Layla,
Watch out taking the fibregel! If you don't drink loads of water it will bulk up your stools and we all know the pain of that!! I used to take fibregel too, until my CRS explained this to me. Now I stay away from the stuff! I drink loads of water still and eat healthier. I rely on 1 satchet of movicol for difficult periods and a tspn of MOM (milk of magnesia) at night. Good luck!