After taking Lasix, you pee more for the next 6 to 8 hours, but the frequency remains high in the first hour after taking it. This medicine is a diuretic, which helps remove extra fluid buildup in the body.  Peeing more frequently is expected after taking it and is nothing to worry about. It’s best to not take this medicine after dinner but take it in the morning instead. At night you’ll frequently have to rush to the bathroom.