adjective

difficult to carry out or fulfil; taxing.

the burdensome responsibilities of professional life

onerous,oppressive,troublesome,weighty,worrisome,vexatious,irksome,trying,crushing,inconvenient,awkward,a nuisance,harsh,severe,stiff,stringent,formidable,an imposition,arduous,strenuous,rigorous,uphill,difficult,hard,laborious,Herculean,exhausting,tiring,taxing,demanding,punishing,gruelling,back-breaking,exacting,wearing,stressful,wearisome,fatiguing,toilsome,exigent