Bo Tox -how it works

I was hoping to get a response from a doctor on this question as I'm about to undergo botox injections to relieve muscle spasms thru my temples and head. It's the one pain source that hasn't been relieved post lorenz implant surgery (07). I can't take most meds that others can and this is basically a last resort. I'd like to know how botox works and if there are any serious risks?