If a person is on ADT for over three years then goes on a drug holiday, he has less than a 50-50 subsequent chance of full testosterone (T) recovery. The older his age and the lower his T when he stops ADT, the longer it will take to recover T and the greater the chance that full recovery will not occur.
Tsumura H, Satoh T, Ishiyama H, Hirano S, Tabata K, Kurosaka S, Matsumoto K, Fujita T, Kitano M, Baba S, Hayakawa K, & Iwamura M. (2015) Recovery of serum testosterone following neoadjuvant and adjuvant androgen deprivation therapy in men treated with prostate brachytherapy. World J Radiol 7, 494-500. www.ncbi.nlm.nih.gov/pubmed/26753064