I got 300 units of Botox underarm sweating and sweating worse than before. What could have gone wrong?

Hi BR.  As another physician has mentioned, Botox (Dysport) injections do depend on the skill of the injector so if you were injected by someone that was not trained well on underarm injections, then it's possible the product could have wound up at the wrong depth.  If it was working with your previous injector, best bet is to return to that person.  Best of luck.

I recommend getting a formal evaluation with a cosmetic dermatologist for hyperhidrosis. Botox works well for improving excessive sweating, however if you have significant amounts you may need oral treatments like glycopyrrolate or surgery. See an expert. Best, Dr. Emer

I typically use about 40-50 units per side injected in 20 locations. If you inject the Botox too deep, it will not work well. If you are getting Botox brand, 300 is too much to be injected in my opinion. I would consider Miradry as this is usually about 1700-2000 and has average of 82% permanent sweat reduction.