How long does ic last?

Long time. If you mean interstitial cystitis (ic), most people have this problem for years. It can come and go, or it can be a chronic problem that is very debilitating. There are medicines and treatments that can help, but the condition tends to recur. Making sure your estrogen levels are adequate is important too, as well as eating the correct diet without spicy foods that could irritate the bladder.
IC. Ic is a chronic condition that we can treat but not cure. It is a lifetime condition that at times will go asymptomatic with flares occasionally.