I took iron when I had UC and it didn't constipate me at all, but technically that is a side effect so it could have been just me. I was incredibly anemic for pretty much the whole 7 years that I had UC. Oral iron supplements didn't help and even iron infusions did very little to help. My iron stores were completely depleted so even if I lost a tiny bit of blood my hemoglobin would drop very drastically. I got my blood checked 3 weeks after my surgery and everything had evened out on its own. Chances are your blood will stabalize on its own within a few weeks if you eat well, but if you feel like you need a supplement I really don't think it'll have any negative effects. Obviously ask your surgeon if you have any concerns.
Ulcerative Colitis since December 2001 (age 15)
in remission for 6 months in 2002 followed by severely active disease
1st j-pouch surgery done on July 30, 2008