Watch Out, Eli Lilly and Novo Nordisk: Amgen's Monthly Weight Loss Drug Has 6 Phase 3 Trials Running -- and It's Coming for Your Patients

Amgen (NASDAQ: AMGN) is betting that the convenience of its weight loss treatment will make it a winner, and it might be right. Its candidate MariTide is a monthly injection that aims to directly challenge the anti-obesity drugs made by Eli Lilly (NYSE: LLY) and Novo Nordisk (NYSE: NVO), which in their original formulations are administered by a weekly injection.

If the program's phase 3 clinical trial data look good, Amgen could enter the market and become a major player despite having no real presence now. So should Eli Lilly and Novo Nordisk actually start to sweat?

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There may not be a real threat to the incumbents here

MariTide is an antibody-peptide conjugate, which in this case means that it's an antibody that blocks the receptor for glucose-dependent insulinotropic polypeptide (GIP), and also carries two peptides that activate the receptor for glucagon-like peptide-1 (GLP-1).

The conjugate's long half-life is what enables dosing only once a month, which could be a major convenience factor for patients, leading to higher market share than competing drugs. In the 592-participant phase 2 trial, adults with obesity and no type 2 diabetes lost 12.3% to 16.2% of their body weight at 52 weeks, against 2.5% on placebo.

The trouble is that those results don't exactly stack up against the competition.

Per one head-to-head trial comparing different molecules for weight loss, tirzepatide, which is the molecule in Eli Lilly's Zepbound, led to 20.2% weight loss, and semaglutide, which is Novo Nordisk's Wegovy, led to 13.7% weight loss after 72 weeks. MariTide has never been tested against either in a structured trial, but its phase 2 data do not suggest that it would dramatically outperform the leading medicines on the market right now.

Amgen's own language on this topic is instructive. The company's commercial chief, Murdo Gordon, told investors in April that it expects to be the best "monthly or less frequently dosed" agent in obesity.

Getting people to switch will be hard

Amgen will struggle to get patients to shift from their other weight loss therapies if it eventually succeeds in commercializing its candidate.

Amgen appears to share that doubt. In May it began an open-label phase 3 study of about 300 adults, moving off GLP-1 drugs and onto MariTide, with results due in 2028. Even if that trial produces some favorable data, it will probably be far too late to matter because by then both Eli Lilly and Novo Nordisk will likely have even newer and better therapies on the market or approaching commercialization.

Lilly's oral drug orforglipron, now branded Foundayo, was approved on April 1. Getting a once-monthly injection is probably a worse proposition in comparison to taking a daily pill, which many patients already do with other medicines anyway. Separately, Novo Nordisk has already filed for approval with its candidate CagriSema in December 2025.

Again, both of those companies, not to mention a few biotechs, have other weight loss candidates in the pipeline.

Amgen's next major weight loss catalyst is Maritime-1, its 3,501-patient obesity trial, which reaches primary completion on Jan. 21, 2027, with the type 2 diabetes study landing the same day.

Until then, Amgen only has a plausible convenience advantage, and it has no evidence in hand that it is beating any of the other players on efficacy or tolerability. Investors don't need to worry that they're at risk of missing the next hot stock on the basis of its published results so far. And, for their parts, Novo Nordisk and Eli Lilly don't need to fear Amgen much right now.

Alex Carchidi has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Amgen, Eli Lilly, and Novo Nordisk. The Motley Fool has a disclosure policy.