My experience may not represent the majority, but...
My experience may not represent the majority, but it's important to know that there is a chance this may happen to you too. I had $400 worth of Botox injections--with high hopes.
Nothing happened after a few days, then after a few weeks, and then, well, never. When I asked my doctor about it he was surprised and was about to ask me if I wanted to have it done again (something that did not work on me anyway?).
He delved a little deeper and it turned out that I had had botulism poisoning in my past--I'd been very sick from it--and had therefore developed a resistance to the botulism toxin that makes Botox effective. Thus, a $400 mistake. I did not know there were instances where Botox did not work and I didn't know about the botulism poisoning connection.
My friend who is a doctor suggested that because there are at least two strains/variations of Botox--A and B--that I may want to consider using the OTHER strain--not the one that did not work. But I am reluctant to put any money into it again.
My adice? The first time you get Botox, get the smallest amount possible to test if it works. If it works, you are lucky and can get more later.