Hello! I took Humira for a short spell (two months) to damp down inflammation before surgery. I got hit with a whole load of steroids simultaneously, so couldn't say if it was specifically the Humira that quelled the inflammation, but I was in remission by the end of the period of use. It's considered one of the big guns for tackling Crohn's, I believe.
I have heard various time frames for Humira. Was told that I should start to see improvement of symptoms after the second or third dosing, and continued improvement from then on if it proved effective. Many others suggest that it took longer for them. First dose was four syringes, second dose of two syringes two weeks later, then a single syringe every two weeks after that until it's discontinued. I had to go into the hospital to have the fist dose administered, and was monitored for any negative side effects for a while afterwards. I assume the monitoring procedure is similar wherever you are, so any immediate side effects should be picked up. I didn't personally find that it had any negative side effects, though people who have taken it for longer periods might want to weight in.
Lots of people seem to complain of pain at the injection site, which I didn't experience at all. I was advised to take the syringe out of the fridge and let it warm for up to an hour before injecting to avoid a painful injection. I think the fluid becomes more viscous when cold, so it's harder to inject.