The thing with the meds is that everyone's body chemistry is slightly different. And yes, this is also true with food. Once again my work with diabetes shows this.

The effect of potatoes on blood sugar should be static for all people, right? Well, it isn't. Patient A will report extreme elevation even with eating 1 spoon of potatoes, so must avoid them like the plague. Patient B does not have the same problem. In fact, potatoes raise glucose, sure, but not that bad. So this patient has potatoes 3 times a week, no problem. However, patient B cannot eat any type of rice (including brown rice and long grain rice,) without a major spike in blood glucose. How does that make sense? Shouldn't all food effect everyone the same? No, it doesn't. Because yes, it is chemical, and yes we all individually respond differently to chemicals.

So, it is the same with meds. With vitamins. With water. With food. With soda. With artificial sweetners. Everything.

So, that's why different meds and combos do not work for everyone. But it's true of all meds. Metformin is not for everyone. Victoza is not for everyone. Even people are allergic to insulin. How crazy is that? Our body makes insulin! But something in it people are allergic to.