Is This Disturbing Trend Bad News for Eli Lilly in the Billion-Dollar Obesity Drug Market?

Eli Lilly (NYSE: LLY) and Novo Nordisk (NYSE: NVO) today participate in one of the most exciting growth markets in healthcare: the weight loss drug market, one that's on track to reach nearly $100 billion in a few years. Novo was the first to launch GLP-1 drugs and see them deliver blockbuster revenue, but it was quickly followed by Lilly, and this company also saw great successes.

In fact, as of about a year ago, Lilly actually jumped ahead of Novo and is now the GLP-1 leader in the U.S. and internationally. This leadership has translated into double-digit revenue growth as well as stock price performance, as investors applauded Lilly's accomplishments.

But right now, is one recent disturbing trend bad news for Lilly in this key growth market? Let's find out.

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Today's weight loss drugs

So, first, a bit of background on these pharma companies' portfolios. Novo sells semaglutide under the brand names Ozempic and Wegovy, for type 2 diabetes and weight loss, respectively. Lilly sells tirzepatide as Mounjaro for the former indication and Zepbound for the latter. These drugs, in injectable format, act on hormonal pathways involved in digestion and therefore help regulate blood sugar levels and appetite. Patients self-inject on a weekly basis.

Demand has been high for these products, even resulting in shortages in the past -- in recent times, though, supply has been able to meet demand since both companies ramped up manufacturing capacity.

The Novo and Lilly drugs have proven to be efficacious and safe, and they are easy for patients to fit into their routines -- all of this has contributed to their popularity. Why has Lilly won leadership in the market? It may be due to data showing that the Lilly drugs lead to greater weight loss. In a head-to-head study, Zepbound helped patients lose an average of 20% of their body weight, while Wegovy generated average weight loss of 13% at 72 weeks.

But these aren't the only weight loss drugs sold by Lilly and Novo. Each has launched new oral weight loss drugs in recent times, and these could represent the next wave of growth for the companies. Novo won approval for oral Wegovy late last year, and Lilly won approval for Foundayo, its oral GLP-1 drug, this spring.

Prescriptions for Foundayo

And this brings me to the disturbing trend that could worry Lilly investors. Weekly prescription growth for Foundayo has remained flat over the past five weeks, FiercePharma reported, citing a July 10 note from Jefferies analysts. This is based on data gathered by IQVIA.

In the 13th week post-launch, the prescription count came in at 19,550. This is compared to the figure of more than 105,000 for the Wegovy pill at the same point after its launch.

This information shows us that doctors haven't been writing more and more prescriptions for the new Lilly drug -- and the oral Wegovy launch appears much stronger. Should Lilly shareholders worry about this disturbing trend?

There are a couple of differences to note. Oral Wegovy is the same drug -- semaglutide -- as its injectables, while Foundayo is a totally new GLP-1 product. So doctors and patients may take more time to get on board when it's not a drug they know well.

Second, major pharmacy benefit managers were on board with coverage of Wegovy as of the first week, but coverage came later for Foundayo, according to FiercePharma.

These elements may have offered oral Wegovy an advantage -- and more momentum at the launch. It's important to note that Foundayo may progressively appeal to doctors and patients looking for convenience: While oral Wegovy comes with food and beverage restrictions, Foundayo doesn't.

Novo dominated the injectable GLP-1 space, and then Lilly gradually built its leadership; so this could happen in the oral weight loss market too. And even if it doesn't, Lilly's 60% share of the U.S. market and deep pipeline of weight loss candidates mean investors shouldn't worry about the initial launch trend of one product. Lilly's weight loss drug portfolio is solid, and the company remains well-positioned to deliver earnings growth and stock performance over the long term.

Adria Cimino 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 has a disclosure policy.