Hello, although lasix may very rarely cause nephritis (which may present with blood in the urine, among other symptoms) this scenario does not sound very likely because nephritis due to lasix is very very rare and also because we wouldn t expect bleeding to cease just one day after stopping the offending drug. Actually nephritis may take weeks to resolve. One more thing to consider is that blaming a drug for any side effect requires investigation to exclude other causes first. In cases of painless bleeding in the urine a thorough check of the urinary tract is indicated. You can start with an ultrasound scan. Other tests (after the ultrasound) may include a CT-scan which depicts the urinary tract in more detail and cystoscopy for direct visualization of the bladder. Note that aspirin may sometimes cause bleeding particularly if an injury occurred. Another potential cause includes a urinary tract infection which is one of the most common causes of blood in the urine. So in conclusion, investigation is required to identify the cause of bleeding. I hope you find my comments helpful! Kind regards!