I am just repeating what I have been taught. I do know from personal experience that the dosage required to exceed bowel tolerance can and will change with both Vitamin C and magnesium. The quality and bio-availability of the Vitamin will also make a difference. Oxypowder is essentially magnesium oxide that is not well absorbed by the body. For most people, over 90% of any mag. oxide taken will be flushed through the colon. For people who do not get good results from large doses of magnesium based laxatives generally have one of these problems: first is being chronically dehydrated. Even when plenty of water is taken, it can be that it is not utilized by the body and simply goes through the system without hydrating the cells. Another cause of lack of BMs can be a sluggish, clogged colon that lacks tone and has so much hard dried fecal matter clinging to the walls that it takes a long time to soften and flush away. This condition may also indicate a lack of good intestinal flora. The solution to chronic constipation can be very complex and require more than a single cleansing protocol.
To bring this back on topic, any kind of detoxification is much easier when the bowels are working. THis includes the chemical flushing resulting from Iodine supplementation.