Before I was prescribed Xenical, my Doctor said if I lose 5% of my body fat in the 1st month, and then 10% in 3 months, then it works for me and my body but she also said if you don't lose that then over 12 months Xenical won't help me. I did lose 5% in my 1st month and when I went back to my Doctor to get more Xenical, I had written how much I lost each week on a piece of paper and she didn't even ask to weigh me, she just read the piece of paper and prescribed me more Xenical.
It's different with every Doctor so just lose as much as you can. Good luck!