As if there weren't enough reasons to buy shares of the cardiometabolic drug juggernauts Eli Lilly (LLY 0.32%) and Novo Nordisk (NVO -0.90%), there's now one more big reason to expect these two stocks to keep climbing.

While this new opportunity will take some time to cook before it's ready to delight shareholders, one of the two companies is making significant headway, so it won't be much longer in the grand scheme of things.

Here's why the case in favor of these stocks just got even better.

This study spells an even more profitable future

Type 2 diabetes and obesity are both major risk factors for developing Alzheimer's disease, and nearly 11% of people over age 65 have the disease. According to the Centers for Disease Control and Prevention (CDC), approximately 15% of adults in the U.S. have diabetes and close to 42% of adults meet the clinical criteria for obesity -- and obesity is a major risk factor for developing diabetes.

In short, these three conditions form a vicious triad that constitutes a serious public health problem. There's a growing body of evidence suggesting that one specific type of intervention could, in theory, tackle all three at once, saving millions of lives and generating billions of dollars in sales along the way.

In a new study published on Oct. 24, analyzing the electronic health records (EHRs) of 116 million people in the U.S., people with type 2 diabetes who were treated with semaglutide, the active ingredient of Novo Nordisk's drugs Ozempic and Wegovy, saw their risk of developing Alzheimer's disease drop by between 40% and 70%, compared to those taking other common treatments for the condition.

The study also found that patients taking other medicines with the same target, the GLP-1 receptor, experienced a significant risk reduction. Furthermore, the research corroborates other prior investigations suggesting that drugs of that same class are likely to be useful in preventing or treating Alzheimer's.

The implications of this study are tremendous for both Eli Lilly and Novo Nordisk, as both already have blockbuster drugs in the market that target the GLP-1 receptor. Novo is investigating whether semaglutide is helpful in treating Alzheimer's directly in a phase 3 clinical trial, but it might soon opt to start another trial to replicate the risk-reduction data that the above study suggested. This way, it could get regulatory approval for an expanded indication on that front.

While Lilly doesn't currently have any clinical programs testing its drug Mounjaro -- which targets the GLP-1 receptor, as well as an additional receptor, for Alzheimer's disease specifically -- it does have a drug called Kisunla that's approved to treat the condition, as well as a few other mid-to-late stage pipeline programs seeking to treat it.

Keep in mind that the market for reducing the risk of an incurable degenerative illness like Alzheimer's is likely vastly larger than the market for therapies devoted to managing it.

Patience will be necessary to see the returns

Novo Nordisk's molecule has the potential to secure a significant portion of the prevention market, as no other interventions have shown comparable levels of risk reduction.

Lilly, on the other hand, still has plenty of legwork to do and may not be in a position to get started with clinical-trial testing its molecule for treating or preventing Alzheimer's just yet. But if the intensity of desired effects of treatment with GLP-1 drugs, like weight loss, is linked to the efficacy in reducing Alzheimer's disease risk, Lilly's medicines would likely be even more effective than Novo Nordisk's. That's because Lilly has already demonstrated that its drugs are more effective at helping patients shed weight.

Either way, the bullish case for investing in both companies is now significantly stronger than before. The hard work of developing their therapeutic molecules and proving their basic safety and efficacy for diabetes and obesity is already done. Their drugs are raking in billions, and demand remains red hot.

Now, with a bit of incremental research and development (R&D) spending, both companies have a solid shot at squeezing many more billions of dollars out of their prior investments. Future investigations testing whether their medicines are capable of reducing the risk of developing Alzheimer's disease in otherwise-healthy people could expand the addressable market.

Investors will have to be patient before they start seeing the returns from these investments. Novo's late-stage clinical trial won't be done until late 2026. It could fail, but given the abundance of very positive data that already exists, that'd be a surprising outcome.

If you're willing to invest with a long-term mindset -- and this is one case where you might consider it -- it would be wise to hold these stocks for a few years. Getting one more green flag shouldn't be too much of a barrier to continue holding or buying more shares.