[georgemcbay]

I have no idea if the tweet was actually directly related to the price drop and lean toward being skeptical of it, but I don't think those other companies also dropping is great proof of that.

Assuming the tweet was believed to be real (by enough of the right people to cause this sort of stock move), the expected outcome would be drops in those other companies as well, since Lilly giving insulin away (the tweet was: “We are excited to announce insulin is free now.”) would obviously cause a large impact on their ability to continue to sell it.