Eli Lilly & Co.’s new weight-loss pill Foundayo has gotten off to a sluggish start, according to new prescription data, an early sign of the challenge the drugmaker will have as it tries to catch up with rival Novo Nordisk A/S.

Lilly shares fell 4.49% while Novo rose over 6%.

Foundayo generated 3,707 prescriptions in its second week, according to IQVIA data cited by RBC Capital Markets analyst Trung Huynh. For comparison, an oral version of Novo’s Wegovy drew 18,410 prescriptions in its second week of launch.

Lilly’s once-daily pill won US clearance earlier this month under a new program designed to expedite access to promising medications. The approval ratcheted up pressure on Novo, whose rival weight-loss pill — launched in January — has been key to its turnaround efforts.

Foundayo is being closely scrutinized by investors who see pills as the next frontier of weight-loss medicine. But until it’s been on the market for two to three months, factors such as sampling programs and the difficulty of capturing telehealth prescriptions will make it tougher to assess its true performance, Huynh said.

“While we believe comparisons early into launch should be considered immaterial, Foundayo’s uptake this week is likely to be received negatively,” Huynh wrote in a note.

Novo declined to comment. Lilly didn’t immediately respond to a request for comment.

Beating Lilly on pills would give Novo a crucial leg up after the Danish drugmaker lost its early market leadership with injectable obesity drugs to its US rival. Lilly’s Zepbound outperformed Novo’s Wegovy on efficacy in a head-to-head trial.

Yet when it comes to obesity pills, Novo may retain its lead because its oral Wegovy is a better product, Danske Bank analysts wrote in a note on Friday.

While the pills haven’t been tested head to head, that hasn’t stopped the comparisons. In a large study from Lilly, Foundayo didn’t lead to the same level of weight loss that Novo showed in a separate trial of the Wegovy pill. Foundayo is easier to use with fewer restrictions, like taking it on an empty stomach and waiting 30 minutes before eating or drinking.

Foundayo is a totally new drug. The Wegovy pill uses the same active ingredient, semaglutide, found in Novo’s injected Wegovy and in Ozempic.