An obesity drug boom is sweeping America, dominating headlines, upending entire industries and stoking belief in the transformational potential of appetite-suppressing injectable treatments like Ozempic.

Why it matters: Behind the wave are plenty of unknowns, including the long-term health effects and how much the skyrocketing demand will drive up health spending.

Driving the news: U.S. demand for the drugs, known as GLP-1 agonists, exceeded supply in 2023, and some analysts predict the market could surpass $150 billion a year within a decade.

• Almost 115 million U.S. adults and children are obese. Some studies show the drugs may make patients healthier — for instance, by reducing heart failure symptoms — and could boost the case for broader uptake.

What's behind the boom

The drugs, originally approved for diabetes, have become popular among people who just want to lose weight, presenting new risk-benefit calculations.

• Primary care doctors, who typically have little training in obesity, have been increasingly cast as gatekeepers and are dealing with heightened demand from patients, including many who are overweight but may benefit from other treatments.
• The barriers include limited insurance coverage. Medicare, for example, covers the drugs for treatment of diabetes but not for weight loss under a 2003 federal law.
• Employers who have long offered coverage for weight-loss tools like bariatric surgery now are grappling with how to accommodate demand for drugs like Wegovy, which is priced at about $1,350 a package, without driving up insurance premiums.
• Meanwhile, rising demand is already triggering shortages. And doctors worry that some patients who can't access the drugs could switch physicians or look to dangerous sources for black-market products to satisfy their needs.

How weight-loss drugs work

How it works: GLP-1 agonists can increase insulin sensitivity, delay the time it takes to empty the stomach and curb hunger.

• The drugs mimic the action of a hormone and prompt the body to produce more insulin when blood sugar levels rise. That extra insulin helps lower blood sugar levels, making them helpful for controlling type 2 diabetes.
• It's not precisely clear how the drugs make people lose weight, per the Mayo Clinic, but slowing the movement of food from the stomach into the small intestine might make people feel full faster and longer, so that they eat less.

The market is dominated by two companies: Novo Nordisk, the manufacturer of Wegovy and Ozempic, and Eli Lilly, which makes Mounjaro and Zepbound.

• Other drugmakers are moving in, sensing major growth ahead — especially if the drugs can be administered in pill form.
• But even as is, GLP-1s have become a social phenomenon and market disruptor. They're driving down the prices of beer, snack and grocery stocks while boosting prospects of clothing brands that could see slimmed-down shoppers update their wardrobes and airlines, which could save on fuel costs.

Why some patients stop taking them

Between the lines: Health experts say they worry about how many patients are stopping the drugs after only a few months of use.

• A Prime Therapeutics analysis in July found 68% of patients who go on GLP-1s for weight loss drop off of them within a year.
• Anecdotally, providers say that's often because either patients can't tolerate the side effects like nausea or other gastrointestinal symptoms or because they've hit a weight-loss plateau and believe the drugs are no longer working.
• It can also be because they've reached their desired weight-loss target, though many go on to regain weight after stopping treatment.
• Primary care providers generally don't have the time to manage and support patients' use of the drugs over months. That's fueled an industry that offers prescribing and support services that themselves could be juicing demand.

Of note: Some health experts believe that the proliferation of GLP-1s is "overmedicalizing" a condition that needs to be addressed structurally.

• This line of reasoning holds that factors including urban planning and the lack of nutritious food are causing the U.S. obesity epidemic.

The risk of adverse events

What we're watching: Regulators in the U.S. and Europe continue to investigate side effects linked to the drugs and whether they warrant regulatory action.

The Food and Drug Administration in January found no immediate link between weight-loss drugs and suicidal thoughts after investigating adverse events reported to an agency database.

• A broad study of patient health records found people taking treatments including Wegovy and Ozempic had a lower risk of suicidal thoughts than people taking other drugs for diabetes and weight loss.
• Post-market reporting systems have nonetheless revealed the risk of suicidal ideation; alopecia, or hair loss; and inhalation of stomach contents. GLP-1 labels in the U.S. already list the risk of suicidal thoughts.
• The European Medicines Agency, which did its own inquiry, said late in 2023 that while no conclusion can be drawn on a connection between the drugs and thoughts of self-harm, "there are several issues that still need to be clarified," and that regulators would revisit the matter in the spring.