Everyone knows that big pharma companies like Eli Lilly (LLY 0.32%) need to get regulators to agree that their medicines are safe and effective before they can make any money. But regulators aren't the only group the companies need appease before shareholders can see a return.

And sometimes, those other groups can throw a wrench into the works, damping long-term growth. As of now, it's looking like Lilly might have stumbled into a pitfall of that type, so let's analyze what the problem is and why it might slow down its momentum slightly.

The international expansion is off to a rocky start

On Oct. 23, Lilly's drug for Alzheimer's disease, Kisunla, was approved in the U.K. by the Medicines and Healthcare products Regulatory Agency (MHRA), following in the footsteps of regulators at the Food and Drug Administration (FDA) in the U.S and regulators in Japan. The U.K.'s regulators concurred with the results of clinical trials suggesting that the drug is somewhat effective for slowing or stopping the rate of cognitive decline associated with the disease for a period of up to roughly seven months. They also found that the side effects associated with treatment, while potentially life-threatening, are acceptable in light of the benefits it can provide.

But, at the same time, the U.K.'s National Institute for Health and Care Excellence (NICE) issued draft guidance indicating the drug was not suitable for coverage within the country's public healthcare system, as it was not cost effective to use given its modest benefits and burdensome medical testing requirements for patients. NICE requested that Lilly provide additional evidence about Kisunla's efficacy, and it expects to deliver a final ruling on Nov. 20. It's doubtful there is any existing evidence that would sway the agency's viewpoint.

NICE estimates that about 70,000 patients living in the U.K. would be eligible for treatment with the medicine. Per Lilly, the direct cost of the drug is $32,000 annually per patient, but from the perspective of a public healthcare system like in the U.K., there are also significant associated indirect costs, like the medical monitoring that patients need to undergo. Assuming that all of the eligible patients in the U.K. would have used the public system rather than buying Kisunla directly, Lilly was looking at an addressable market worth more than $2.2 billion in sales annually.

It now looks like the chances of realizing that potential revenue are slim to none. Worse, it's now clear that regulators in other countries with public healthcare systems may be inclined to agree with NICE and decline to offer coverage for Kisunla. In other words, Lilly's bid to go international with the drug might fall flat on its face. And that would be a new headwind for the growth of its top line, and by extension, the growth of its stock.

Keep the big picture in mind

As grim as the likely loss of the U.K. market for the drug may be, Lilly is far from helpless, and the damage, while notable, might not actually drag on its growth by a noticeable amount if its research and development (R&D) pipeline continues to deliver blockbuster drugs for other indications.

Before NICE's decision, Cantor Fitzgerald's Louise Chen estimated Kisunla could bring in about $2 billion in annual revenue by 2029. For reference, its trailing-12-month revenue is $38.9 billion. So, while the revenue estimate is likely to be reduced, it's important to remember that the drug was always going to be just one modest component of the company's top line, especially considering it will be launching many other medicines between now and 2029.

It still has 20 programs in phase 3 clinical trials, including one for treating Alzheimer's disease that's based on a different molecule than Kisunla. Many of those programs will go on to be approved for sale.

In other words, while there's no way to interpret this new development as being good news for shareholders, the investment thesis for this stock is still very much alive and well.