The first advice authors give is not to use chemical drugs while on UT. The risk is an overdose and the two just don't mix. Any natural remedies, vitamins, or natural treatment is OK, but no allopathic drugs. If you want to practice UT, you should stay off the drugs two days before starting the therapy.
Some advise taking just a bit of urine at first while cutting down on the drugs. Cut down very very slowly and go towards larger quantities of urine but all this with lots of monitoring. If cutting the drugs is "life threatening" you have to be extra cautious and have a trained and qualified doctor or naturopath follow the situation.