FYI, I did lots of research a few years ago on HGH and CF patients. It seems many other countries, other than the US use HGH from an early age with CF patients.
My brother (although not prescribed by his CF doctor) took HGH for a few years when he was in his early 20's, and honestly, I had never seen him look so good, he had very few hospitalizations and was rarely sick. (He was a personal trainer and got it, I believe from an "anti-ageing" clinic).
Do your research, and talk to your docs. But I would highly recommend it. It has several benefits other than just the weight/height gain for CFers...