My 13 year old PKUer has been on this same product for a number of years. In the past, it has been very difficult to transition him to new formulas when his was discontinued, and the transition took several months. This time, we had no transition time. He just had the last of his formula and we are waiting on his substitute product to arrive. I’m not sure he’ll drink it. He is already considered underweight for his age because his protein restriction makes it very difficult, and sometimes impossible, to get all the calories he needs in order to grow. I am very concerned that this supply problem will only decrease his calorie intake even further, causing even more problems with his height and weight growth.