if I had to guess anything, it isn't just the caff.
i know of another brand that uses magnesium in their orastan-a clone. it is called winabol. it contains 200mg per 50mg cap (among other things like potassium, b6)
so if the new furazabol is anything like this, the combo of caffiene + mag in most will cause you to sh*t big time, esp. @ higher dosages.
this is why I always recomend furaguno to people. fura contains only the active ingredient in each "tablet". 33mg, and you get 90 tabs, so your only 1mg short of other products, it isn't going to matter much.
when I used furaguno, I stacked it with the rec. dosage of winabol, and used furaguno @ 198mg's, and then took the rec. dosage of 100mg of winabol to take it over the top. it totaled 298, not 300, but close enough, and I was stacking with hd, which i respond wonderful too. so....
in the end, thats my theory, and recomendation. and if you wanna run fura by itself, you'll need to use like 600mg. thats alot of money.
it would be easier to buy the methylated version off the black market.
i also feel the same way about hd. if you are needing to go over 75mg's, quit it, and go buy some oral turinabol.