My doctor is Dr. Konstan who did the study on ibuprofen back in the day. Right after it was approved I went on the treatment. I started the high-dose ibuprofen when I was 13 years old and was on it for 13 years up until I got pregnant last year.
I'll just give you the info from my experience with it...
I was skinny and my PFT's were around 60% when I started the treatment. By the time I was in my late teens/early 20's, I had no problem gaining weight and keeping weight on (even overweight a bit) and my PFT's rose to 90%'s. I really do believe that the ibuprofen helped maintain and improve my lung function by keeping the inflammation at bay. Because of my healthier lungs, I was able to gain weight and my whole body was healthier overall.
It is a very controversial treatment in the CF community due to the side effects of ibuprofen. The side effects are usually gastric related, but it can also effect the liver and kidneys. I had severe gastric side effects from it, but I was able to control it somewhat with other meds. Before I came off it when I was planning to get pregnant, I was already considering stopping the treatment due to my stomach issues. I was pretty much in constant pain from the gastritis that it was causing me. Ibuprofen is just so irritating to the stomach lining.
A year later, I am stomach pain-free and only deal with minor GERD. My lung function has remained stable so far and now I am using Zithro MWF to help the inflammation instead.
PM me if you have specific questions about it.