To clarify, we still use the "11-x" system from the book, so it's easier to become addicted to a force 8 foci than a force 2, force 8 would only require 3 failures whereas force 2 would require 9 failures.. The ratings are all the same for everything, it just cuts down on tracking what week you last used what drug in, etc. I edited the first post so that it will make sense now, thanks!
I personally don't have a problem with edge use, as it is such a limited resource in terms of its rate of refresh per game session. If people want to prioritize not becoming addicted over other uses, I think it actually adds to the tension a bit, since they know they won't have it later in the day (or even just the combat ahead) to use on something else.
As to the higher risk, yeah that's a big part of why we house-ruled it, drugs felt a little too easy to use before, in the risk/reward sense. The only drug you can get addicted to in 1 shot is Nitro, as it's the only rating 9 that requires both checks.