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The stock jumped 13% to $315.50 in early trading, the best performer in the Dow Jones Industrial Average and S&P 500 Friday. Coming into Friday, shares have declined 3.3% this year but have gained 18% from 12 months ago. The shares have risen four of the past five days through Thursday, and look set to make it five out of six.

Amgen is trying to carve a niche for itself in the fast-growing market for weight-loss drugs that suppress appetite. Eli Lilly and Novo Nordisk currently have successful products on the market. Pharmaceutical giant Pfizer also is working on its own weight-loss product, but was dealt a setback earlier this year when it stopped working on one drug because of  strong side effects.

Analysts at William Blair led by Matt Phipps upgraded Amgen stock to Outperform after the results.

“We see MariTide as having multi-blockbuster potential despite needing to penetrate the current duopoly,” they said. “Amgen has the capacity and expertise to maximize development of the asset.”

The question for the company now is how strong its pipeline of experimental drugs remains. The company said it will have results from Phase 2 trials of MariTide later this year and that it already is planning a Phase 3 program.

Analysts at Mizuho led by Salim Syed were cautious after the results. 

“While we acknowledge perhaps the seemingly more upbeat tone and positive qualitative commentary from management” on the obesity drugs, “a lot of questions remain unanswered,” they wrote in a research note.