modified oxytocin - vasopressin di - or tri - peptides wherein an amide group is replaced by a group selected from ## str1 ## -- ch 2 nh --, -- ch 2 o --, -- ch 2 s --, -- ch 2 so --, -- ch 2 so 2 --, -- ch 2 ch 2 -- and -- ch ═ ch -- are described as well as methods for their manufacture , pharmaceutical compositions and methods for treatment , especially of cognitive disorders , depression , morphine dependency and parkinsonism by adjunctive therapy .