Q. Someone that suffers from hormonal imbalance and was instructed by doctors to maintain a diet of protein and vegetables to avoid significant symptoms of weakness, fatigue, depression and anxiety. As fish is also rejected, can one eat chicken during the nine days in that medical condition?

A. Mishna Berura (551: 61) rules that someone is ill even if he has recovered but not completely, he is allowed to eat even mammal’s meat. See also Nitey Gavriel (Bein Hametzorim 38: 7) quoting Boruch Ta’am.
Horav Shlomo Miller’s Shlit’a opinion is that if it is a doctor recommended diet one may be lenient.

Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit”a