Truth ___ (spy movie drug) (5)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
serum
(Other definitions for serum that I've seen before include "Antitoxin derived from blood" , "Watery liquid as from blister, or fluid in blood" , "Blood component containing antibodies, used in immunisation" , "Watery fluid from animal tissue" , "Muser in blood" .)