Tolterodine XL and Detrusitol XL contains a drug that belongs to a group of medicines called antimuscarinics. Tolterodine is used to treat symptoms of overactive bladder syndrome. If you have overactive bladder syndrome, you may notice that you are not able to control your urine voluntarily, you feel a sudden and urgent need to urinate without warning and/or you increase the number of times you urinate during the day. Both Detrusitol XL and Tolterodine XL is a modified release formulation meaning that it releases the drug in controlled fashion and may not require administration as frequently as other Tolterodine formulations.