The next time I went, I asked for less- 16 units I think. I got it maybe 6 or 9 months later. Same headache, not quite as bad.
While your muscles are frozen, you re-train yourself not to frown, which is great! I mean, you can try, but nothing will happen and your brain gets confused trying to do it.
6 months after that, I think it wore off, because I could squeeze my muscles together into a frown again. The thing was, though, hardly any 11s anymore! Yay success! I'm trying to be pro-active about doing things when I notice them, to slow aging and one thing I heard was you can retrain muscles to not frown and also by relaxing them with this process you can erase early signs of this stuff. Seems to be true in my case.
So I wanted to see "how low I could go" and still maintain progress. I got 10 units. The doctor looked like "well, you'll learn that won't be enough to do anything." Well in fact, it did freeze those muscles, but very selectively and no headache! Yay! Plus it's cheaper obviously because they charge per unit.
I might get a touch more next time- I'm thinking maybe 12 units? I'm happy with the progress.
P.S. I heard that the glabella region is the primary area that the FDA approval is for. When I hear of people doing it all over, like crows feet or near the mouth etc. I get nervous for them. It really does freeze those muscles but good, I mean good thing it wears off but I would be nervous paralyzing something you shouldn't, and getting a weird droop. I would be a minimalist here and go as low as you can.