The Connecticut woman who underwent a face transplant five years ago after being attacked by a chimpanzee is back in a Boston hospital after doctors discovered a "moderate" rejection of the transplant.

Charla Nash said doctors have decided to end an experimental drug treatment and put her back on her original medication in the hopes of reversing the rejection.

Dr. Bohdan Pomahac, director of Plastic Surgery Transplantation at, Brigham and Women’s Hospital, said in a statement that the viability of Nash's face transplant is not in jeopardy.

"Overall, she is doing well. Charla is currently experiencing a moderate rejection episode, which face transplant patients experience on occasion. Charla was previously participating in a research study that is designed to determine whether it is possible for composite tissue allograft recipients to safely taper off of conventional anti rejection medications," the statement says.

Nash is expected to leave the hospital in the next day or two.

"We expect this rejection episode to be resolved within the coming week,” Pomahac said in a statement.

Nash had been taking part in a military-funded experiment in which doctors at Boston's Brigham and Women's Hospital tried to wean her off the anti-rejection drugs she had been taking since the 2011 operation.

“I appreciate everyone’s concern. I feel perfect. I didn’t even know I was having a rejection episode," Nash said in a statement. "While I am disappointed that I cannot continue in the research project, I am proud of my contributions to date, and am hopeful that it will help those wounded serving our country, and others needing transplants in the future.”

She told the Associated Press she would appreciate any prayers.