deadening
noun.
the act of making something futile and useless (as by routine)
Synonym: constipation, impairment, stultification
adj.
so lacking in interest as to cause mental weariness
a boring evening with uninteresting people|the deadening effect of some routine tasks|a dull play|his competent but dull performance|a ho-hum speaker who couldn't capture their attention|what an irksome task the writing of long letters is|tedious days on the train|the tiresome chirping of a cricket|other people's dreams are dreadfully wearisome
Synonym: tiresome, tedious, slow, irksome, ho-hum, dull, boring, wearisome