Eli Lilly (LLY) is planning to advertise its blockbuster weight loss drug, Zepbound, for the first time next month.

Despite investor and industry recognition of the branded GLP-1 drug, "unaided awareness of Zepbound ... is actually not very high," CEO David Ricks said on an earnings call Wednesday morning.

The company missed Wall Street expectations on the top and bottom lines, including on the drug itself — reporting $1.3 billion in sales for the quarter compared to an expected $1.7 billion.

The company's stock dove more than 13% in early trading Wednesday.

The FDA first approved the drug in November 2023, and sales reached over $1 billion by the second quarter of this year. To date, Lilly's total revenue since the drug's launch, without advertising, is $3.2 billion.

"We launched this drug almost a year ago and have done no advertising. So I think it is time to introduce the brand so people are aware of that when speaking to their doctor," Ricks said.

The company has had to wait for supply to meet demand, which the FDA determined was the case earlier this month. However, that decision is under reconsideration after pushback from compounding pharmacies that have been filling the shortage in the interim with unapproved copycats of Lilly's tirzepatide drugs, including the diabetes medication Mounjaro.

Lilly's new CFO, Lucas Montarce, said the company has much more confidence in the supply moving forward. He added that the total addressable market for Zepbound has only reached 5% penetration — so the company needs to do what it can to drive up patient awareness, including through the direct-to-consumer platform LillyDirect.

The decision also comes at a time when Lilly is increasingly taking market share away from rival Novo Nordisk (NVO), which continues to face supply constraints.

"If we look at the last 90 days [and] 180 days of US prescription growth, both brands are growing aggressively. We've now passed Wegovy in the weight-loss sector," Ricks told Yahoo Finance in an interview Wednesday.

In the diabetes space, "we're not quite [pacing] Ozempic with Mounjaro, but every week we basically eat up [market] share," he added.

In weekly prescription data ending Oct. 18, Eli Lilly's Mounjaro captured 33% of market share, or a year-over-year jump of 79%, while Novo's Ozempic was at 47%, or a year-over-year jump of 39%. But the numbers have shifted in favor of Lilly this year, according to data compiled by JPMorgan analysts.

In February, weekly data ending Feb. 16 showed Mounjaro at 29% of the market versus Ozempic's 44%.