"The weather in the Northeast and Midwest and Mid-Atlantic, it's obvious, it was horrible," said Chris Raymond, an analyst with Robert W. Baird, in a phone interview Thursday. "It's common sense, thinking about AMD, it's age-related, meaning it affects the elderly, so who's going to be perhaps less able to get to the doctor's office during bad weather?"
It was Regeneron's weakest showing for the drug since the third quarter of 2013, RBC Capital Markets analyst Adnan Butt wrote in a research note.
NPS Pharmaceuticals, maker of the drug Gattex for short bowel syndrome, dropped as much as 10 percent Thursday after reducing its 2014 forecast because of a "challenging January and February." Why? "Severe winter weather," CEO Francois Nader said in the company's release.
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NPS now expects 2014 sales of $100 million to $110 million, down from a previous forecast of $110 million to $120 million.
But it may not all be gloom and doom. Baird's Raymond points out that delayed sales from the first quarter could provide a boost to the next one.
"Especially with Regeneron, I would be kind of licking my chops because I think this means you're going to see a rebound," he said. "You'll see some carry-through from patients who would have been treated in the first quarter, so we'll see bigger numbers in the second quarter."
And, hopefully, some sunshine.
—By CNBC's Meg Tirrell.