Shares of Biogen  (BIIB - Get Report)  were up close to 40% this morning after the company said it plans to pursue regulatory approval for aducanumab, a drug for early Alzheimer's disease.

The stock has come down a bit since, but is still trading close to 25% above where it opened this morning. Even if you missed out on the initial pop, it may not be too late according to Jim Cramer:

"Judging from what we can tell, it's very unusual for the FDA to say, look, you know, we really want this. So that's the story of the day. And even though it's up 79, 80 points, I, I hate to say it, but maybe you buy some now and if it comes in by more, it's too big. It's too big a drug."

Watch the video above to see what else Cramer had to say about Biogen's big news.

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