I am 39 years old and have been on Kuvan for 6 months. I am responding very well. I am currently taking in 1250 mg.of phe daily and hoping to increase even more. My levels are ranging from 1.8 to 4.2 My eating has changed alot. I tried chicken for the first time 2-27-09. I take 15 tabs daily and the only side effects I have had are headaches.