They may not get a patent extension on Botox that their looking for because even though they may have found a new indication for its use, the FDA knows that a majority of their sales goes towards aesthetics sales and will not be beneficial to migraine headache patients. They may not grant it, which means that Botox, their biggest money maker, will be a generic target. There are already plenty of companies ready to make generic Botox as soon as that patient expires.
Now Juvederm is questionable in its safety. And there is still no guarantee that their bimataprost eyelash growing product is going to get FDA approval. It works, but there are potential side-effects that no one seems to be talking about much. Given the FDA's new found concern for end consumer safety, the FDA may be the only one that talks about it....and does something about it.
This is a company that makes money because they have exclusive market protection on the products that they sell, and they are losing some of those protections. Their new products in the pipeline may not get approved by FDA. If FDA decides to go over the statistics that Allergan's phase four trial contractor came up with it could hold up this new product. All this adds up to the declining stock price that your seeing today.
If all this comes to pass, the stock price goes down. If FDA gives Allergan a pass, as they have the last 8 years, the stock price goes up. It all depends on whether Allergan continues to get FDA patent protection or not. Nothing more, nothing less.
Botox does not go off patent, and companies can not make a generic version of it; it is a biologic. The company would need the exact bacteria and means of making Botox, and Allergan will not just give it to them.
And yes, the eyelash medication will have side-effects: darkening eye color is one.