While I've not taken Humira long term (I think I only took it for 3 weeks or so before switching), when I was taking Enbrel (the same class drug as Humira), I definitely felt it wearing off before my next injection. At one point, I was taking 2 enbrel injections/wk. I would imagine that Humira would be similar since it is also a tnf inhibitor.
Elcamino