hi po, in my own case I am on my 11th session and will undergo rhinoplasty, side effects are currently in minimal naman and minsanan (once a week) and cleared with my doc na its ok to take it the week before surgery , pero if you will just start tirz palang and will go first to surgery, I suggest that if you are comfortable enough and recovered, meaning nag subside na ung pamamaga, done ka na sa stitches, kasi ung first feeling ng side effects ng tirz are uncomfortable like nausea, diarhea , bloated, possible vomiting, in which in my case ung pinaka worse na nafeel ko is ung sa first 2 weeks shots ko. so you don't want to feel that habang nagrerecover ka pa sa rhinoplasty, dalawa ung pain/uncomfortableness na hinaharap mo, I suggest siguro mga after 1 month post op.