There is always a chance that adding a chemical to our system can stall or slow down the process of fat loss. Chemicals are acid in the body. When the body becomes acidic, it has to retain water and fat to neutralize the acid. This could be interpreted as a stall on the scale. However, stress is not helpful when it comes to weight loss and being in pain (for instance, a headache from such a fast detox) can certainly cause stress. Taking an Excedrin to help can help to reduce stress levels, and keep you on track as you navigate the first few days of the Skinny Up! Protocol and the major detox that you can experience during that time.Use your best judgement and do what you need to in order to take care of yourself. In other words, yes, you may use an over the counter pain med, but don't overdo it.