Bernstein is actually quite positive about Victoza, but he says that in his clinical practice he has found that it loses effectiveness after about six months. I've never hear an explanation of why it stops working, perhaps your body just adapts to the medication. Victoza and Byetta worked for me, but only for 2-4 weeks after which it stopped working. It was wonderfully effective while it worked tho.
Bernstein's solution is to rotate Victoza with Byetta switching every six months. Perhaps you work with your doctor to give that a try?