Menstrual blood does not affect urine drug tests, according to Occupational Drug Testing, LLC. However, certain medications and alcohol consumption may affect test results, so it is recommended that individuals provide testing technicians with a list of medications they are taking as well as abstain from alcohol prior to testing.
Excessive water consumption can temporarily dilute the urine, which in turn can affect the results of a urine drug test, according to Forensic Laboratories. Additional factors that can alter urine drug screens include bacteria or mold in urine samples, and insufficient amounts of urine. Medical conditions such as hepatitis-C and cirrhosis of the liver can also cause innaccurate results.