Slavefic in which young actor Jensen signs up for a medical trial and gets more than he bargained for. Well written apart from the odd inconsistency.
Wow, took me a month to read this super long fic, the longest in the supernatural fandom on AO3. This epic covers only 7 months in time excluding the 'Then' sequences and the epilogue. A well written fic with excellent world building, some scenes are not for the squeamish.