Ah -- the stomach pain. Since most long-termoxy abusers (I'm guessing here, but just "most") end up snorting the suff, there isn't the same direct, immediate contact with the stomach. Have you tasted the stuff? It's extremely bitter -- either very acidic or very alkaline. Either way, it's an assault on a sensitive stomach, especially if you chew them.
NOTE: Could you clarify what preparations, and for how long, you've been taking?