yes, i have done an 18 day urine fast as well as a few shorter fasts over the years. however, i have now switched to Water Fasting because i had found it so much more effective. i had some extremely refractory symptoms for nearly 2 years and i didn't find that the UT fast helped very much at all and i would never do it again. the Water Fasting has been really successful - i am currently on day 16 and it is going really well. i think that this is because the urine is unnecessary if not counterproductive - the body already knows what it needs to heal because of its innate intelligence.
if you want to read up on water fasting, this is the best resource: