From what I've read, it's a prostanazol compound and the only thing (chemically) differentiating it from winny is that it's missing the whole 17aa group- which is what makes winny MUCH more bioavailable, and, accordingly, more liver toxic. Apparently the 17aa group was removed (to make it legal) and replaced with a different (non-toxic) group that allows it to be absorbed through the lymphatic system. It has significantly lower bioavailability (which is why the effective dosage is so high), but its also not liver-toxic. I've read that the b/a is around 10-15%; so, theoretically, if you take enough, its like taking a non-toxic winny: making it ideal for stacking. Plus, I've been taking a pretty low dose of var, as well as some solid liver supports, while running the katana anyways, so I'm not overly concerned about whatever minor strain it might be putting on my liver.