Is he losing weight?
Maybe he's cut his fat content too low.
I used Xenical many years ago when it first came out. I lost 5st, then I felt like it had stopped working. I used it again a few years later and it seemed to be hit or miss if it worked.
At times I'd be surprised that a low fat meal of chicken breast would have me leaking oily stool.
I found a few tablets I'd forgotten I had and been using them for a few days and they seem to be working.