Is it a laxative?

P.S. And the correct answer is, no if you are doing the Master-Cleanse to the "t", by the book. And yes if you are doing a modified Master-Cleanse - you being the moderator (not us), of course.

Yes it is all natural.

I believe its normally used for cleaning the colon.

Just as an aside.
I was once shown that rat poison is "all natural". Apparently there are no man made ingredients in rat poison.

In my opinion, products like Oxypowder may be superior to the traditional herbal laxative tea and salt water flush. Both of these methods can be very irritating to the system and there is a risk of side effects. Herbal laxatives can produce dependency in some people in a relatively short time. Others can absorb too much salt in the SWF (Salt-Water-Flush) and risk bloating and even blood pressure problems. The magnesium oxide products are generally safe, but care must be taken to stay fully hydrated at all times. I would suggest trying the lax tea and SWF (Salt-Water-Flush) for the first three to four days to insure the bowel is stimulated and the system is flushed clean of all recent fecal matter. After that, a magnesium oxide product will keep the colon cleaned out and may even allow for deeper cleansing in the bowel and even small intestine.

The most important thing is to do what is best for your body and your needs. This will take self experimentation, and hopefully reporting both the good and the bad results of this experimentation.