"Mounjaro is the story here," Bloomberg Intelligence analyst John Murphy said. The company's guidance raise, meanwhile, "looks conservative if Mounjaro's huge first quarter sales beat is indicative of true underlying market demand."

Related: New weight loss drugs: Social media fuels huge demand, but not all are FDA-approved

One of a group of highly effective new weight loss drugs initially developed as diabetes medications, Mounjaro is a weekly injection that replicates the effects of hormones in the body that help people feel full.

Wall Street has enormous expectations for the field, and sees Mounjaro soon becoming the biggest drug, surpassing Novo Nordisk A/S's Wegovy and Saxenda, two earlier obesity drugs. Novo's diabetes drug Ozempic is also used off label for weight loss. Mounjaro is designed to mimic more hormones within the body than Novo's drugs.

Mounjaro, also known as tirzepatide, was approved by the FDA last May as a treatment for type 2 diabetes, and launched in June. It is expected to become a blockbuster this year, with projections of nearly $3 billion in 2023 sales. Investors also say Mounjaro's annual sales should exceed Wegovy's by 2026, according to estimates compiled by Bloomberg. Both drugs are expected to generate over $10 billion in sales by then, according to analysts.

Analysts are even more confident in Mounjaro now after Lilly shared new study results early Thursday. In a large, late-stage clinical trial of people with diabetes and obesity, Mounjaro helped patients lose up to 15% of their body weight, or around 30 pounds.

The study showed slightly less weight loss than another large Mounjaro study released last year, which showed weight loss of as much as 50 pounds, likely because the participants this time also had diabetes. Shedding pounds can be especially challenging for people with diabetes. Novo's Wegovy, by comparison, produces average weight loss of about 30 pounds.

BMO Capital Markets analyst Evan David Seigerman added that the new trial data "validates Mounjaro superiority by a long shot."

"These data reinforce our view that Mounjaro is the best injectable option for weight loss," he said.

Lilly intends to finish its submission for FDA approval of Mounjaro as a weight loss treatment in the next few weeks. The regulator could make a decision later this year, the company said.

Even without FDA approval for weight loss, Mounjaro has been embraced by doctors and patients alike as a weight treatment, contributing to a two-month shortage that Lilly says resolved in February. Other treatments, including Novo's Wegovy and Ozempic, have also been in short supply.

Investor excitement about Mounjaro has helped boost Lilly shares by about a third over the last year. Rival drugmakers like Novo have also risen. Other companies rushing to develop obesity medications include Pfizer Inc., Amgen Inc., Novartis AG, AstraZeneca Plc, Takeda Pharmaceutical Co. and Boehringer Ingelheim GmbH.

Lilly also reported first-quarter earnings early Thursday, in which it increased adjusted earnings-per-share guidance to a range of $8.65 to $8.85, increasing its guidance by $0.30 per share. Revenue for the year will be $31.2 billion to $31.7 billion, Lilly said, increasing its prior outlook by $900 million.

The drugmaker's adjusted first-quarter earnings were $1.62 a share, short of analysts' expectations of $1.72. The company cited declining COVID drug revenue. Revenue was $6.96 billion, slightly beating the average estimate of $6.9 billion.

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