Iron Infusion

All forms of iron supplements can cause GI upset. Generally IV supplement of iron is the least upsetting. But upset still can occur.

Venofer is an older preparation (iron sucrose) which takes a long time to infuse....
Ferric Carboxymaltose (Ferinject) is much quicker and is more widely used these days.
IV iron shouldn't bother your UC, though some people can be sensitive. They often infuse a small amount, and if there is no reaction they go ahead with the rest.

I have found liquid iron supplements worked for me when I had low iron levels. Also, believe it or not, cooking in an iron cast pan can help increase your iron levels.

Cosmofer gave me an anaphylactic reaction. I wouldn't touch Venofer with a 10-foot bargepole.

Ferinject though has been fine. Have had several infusions over the last few years and not had a single bad reaction.

If it's possible, I'd switch to Ferinject. I've never had any GI symptoms from it.

I have finally found an oral iron supplement that I can tolerate. It's a spray, which bypasses the GI tract and therefore any GI side effects. Whether it works or not, it's too soon to tell. I'll have to wait until I get my ferritin and haemoglobin levels tested again, which - given the coronavirus - probably won't be any time this year.

Mind, it would help if I could remember to take it every day...

This one.

https://betteryou.com/iron-10-oral-spray

It's a UK company but says it ships worldwide.

I hope it helps!