Watch Out, Eli Lilly and Novo Nordisk: Viking Therapeutics Just Started Testing a Weight Loss Drug That Goes Beyond GLP-1

The human appetite has more than one off switch, and drugmakers like Eli Lilly (NYSE: LLY) and Novo Nordisk (NYSE: NVO) are doing their darndest to identify and develop a medicine to target every single one.

On June 24, Viking Therapeutics (NASDAQ: VKTX) announced a phase 1 trial for one of its candidates that's attempting to flip one of those as-yet unmedicated appetite switches. That marks its first obesity candidate working outside the incretin pathway that includes GLP-1, or glucagon-like peptide-1, the hormone behind Ozempic and Wegovy and one of two hormones behind Zepbound and Mounjaro.

Let's take a look at this program and determine whether it's really going to be a threat to Novo Nordisk and Eli Lilly.

Image source: Getty Images.

This hormone is already a hot target

Amylin is a hormone produced in the pancreas that is released with insulin after a meal, activating receptors in the brain stem that promote the feeling of fullness, and also slowing stomach emptying. That pathway is adjacent to the one that the GLP-1 medicines use, so it could technically be targeted by a combination therapy affecting both.

VK3019, Viking's new candidate, is a dual amylin and calcitonin receptor agonist. Additionally targeting calcitonin activation is meant to yield metabolic effects amylin alone does not; preclinical animal model data showed that the combination led to up to 8% weight reduction against controls.

The new phase 1 trial, announced on June 24, is being conducted in adults with a body mass index of 30 or above, and the candidate is formulated as an injection. If Viking's dual targets work as desired, the company could be on the way to producing a leading next-generation weight loss candidate -- but its bigger competitors are way ahead of it.

Eli Lilly reported phase 2 results for eloralintide, an amylin receptor agonist, in November 2025; across dosing arms, patients experienced mean weight reductions of 9.5% to 20.1% after 48 weeks, against a loss of 0.4% with placebo. Phase 3 is already in progress.

Novo Nordisk has gone even further. Its candidate cagrilintide produced 11.8% weight loss against 2.3% for placebo over a 68-week period; its phase 3 program began in late 2025. A combination drug program called CagriSema, which contains cagrilintide plus semaglutide (the active ingredient of Ozempic and Wegovy), was submitted to the U.S. Food and Drug Administration (FDA) in December, with review expected this year.

The combination approach is popular, too

So Viking Therapeutics won't be the first to market with its amylin program, even if its clinical trials go swimmingly.

But Viking already owns VK2735, a dual agonist of the GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) receptors that's in phase 3 trials. Pairing it with an amylin candidate like VK3019 could deliver the results that would keep the company relevant in the next round of the competition in weight loss drugs. And, as a pre-revenue biotech, it wouldn't even need to win that much of the market for its shares to see meaningful gains.

The catch is that Lilly is already running that exact play. A phase 1 study of eloralintide administered with tirzepatide (Mounjaro, Zepbound) has completed, and a phase 3 trial adding eloralintide to a weekly incretin is enrolling now. Viking is thus trying to assemble what both incumbents built years ago.

That means VK3019 is going to need to be substantially more effective or more pleasant to take if the biotech is going to secure a large share of the market. It's certainly possible -- but it's very risky to bet on it.

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