Don, Victor
this may apply for you both. The lidocaine: mainly the last two weeks of radiation. I used it when I wanted to eat/drink or speak, unfortunately the effect does not last long.
I am a bit hazy on the details with the morphine But this was the last 2 (3) weeks of the rads .... and then for 10 days afterwards. However, I did start with it gradually and also tapered it off. I never got up to the prescribed dose. As Deb says the pain meds cause constipation. That said, take as much drugs as needed, there is no point suffering needlessly.
I had problems first after about 3.5 weeks. Counting from my second IMRT start. (see signature). However, I had a yeast infection, once this was treated things were ok again for one more week. That is something to watch for as well.

The liquid diet compacts into "bricks" amazingly well I did not think this possible either. This is something easy to avoid once you know that it may happen.

M