I don't know the official answer to this question, I just know that I would absolutely take something. If you are suffering unbearably, it might be harder to continue for day 2 and 3. When I first began my fast I had a horrible rotten headache and I knew at least part of it was caffeine withdrawel, so I had one cup of tea, the next day I had half a cup on on the third day I didn't have any. It's probably not encouraged, but it was the best way I knew how to manage the fast. If you need a little aspirin on the first couple day, just know that you will still be detoxing your body and probably get rid of what causes your daily headaches.