GEOFF BENNETT: Tonight, we're kicking off a new series all about GLP-1 medications.

Hailed by some as miracle drugs, GLP-1s have surged in popularity in the past few years.

An estimated one out of every eight Americans is now on some version of them.

And scientists continue to research new potential uses.

But with that rapid expansion, there's a growing list of questions and skeptics.

Our William Brangham starts our coverage of GLP-1s: Reshaping America.

WILLIAM BRANGHAM: The drugs are called glucagon-like peptide-1 receptor agonists.

Chances are, you have heard a lot about them, or at least some of their brand names.

NARRATOR: With Wegovy, you can live lighter.

NARRATOR: Who have taken Ozempic.

NARRATOR: Ask your doctor about Zepbound.

WILLIAM BRANGHAM: Today, these drugs are best known for their ability to help people manage their diabetes and to lose weight, sometimes at eye-popping rates.

SERENA WILLIAMS, Professional Tennis Player: GLP-1s helped me lose 31 pounds.

WILLIAM BRANGHAM: They have been promoted by celebrities.

WOMAN: GLP-1s to quiet the noise.

WOMAN: Wegovy now comes in a pill.

WILLIAM BRANGHAM: And now taken by millions of people across America.

MAN: The drugs really do what they say they're going to do, and they do it very well.

WOMAN: I started losing weight almost immediately.

MAN: So, so helpful.

The weight just melts off.

WILLIAM BRANGHAM: Researchers first discovered the GLP-1 hormone decades ago.

It helps regulate blood sugar by stimulating the body's release of insulin.

In the 1990s, scientists realized that the venomous lizard the Gila monster produced a molecule very similar to GLP-1.

That led to the development of the first GLP-1 drug to treat diabetes in humans.

It was approved by the FDA in 2005.

JULIA BELLUZ, Co-Author, "Food Intelligence": When we give people very high doses of synthetic GLP-1 in the form of these drugs, we get this array of astounding effects, from better managed blood sugar to weight loss, that we basically haven't seen outside of bariatric surgery.

WILLIAM BRANGHAM: The first GLP-1 specifically for weight loss was OKed in 2014.

For a while, researchers thought the weight loss benefits of GLP-1s started in a person's gut.

JULIA BELLUZ: But it turns out how they work for weight loss is quite different.

The drugs actually work through the brain to reduce appetite and reduce this thing that a lot of people refer to now as food noise or cravings or preoccupation with food that so many people feel.

And people eat less and end up losing weight as a result.

WILLIAM BRANGHAM: In some cases, patients can drop up to a quarter of their body weight.

And doctors are seeing other benefits too, like reduced inflammation and improved cardiovascular health.

But that's not all.

MAN: Could they be a magic bullet for cancer too?

WOMAN: Sleep apnea.

WOMAN: Addiction.

WOMAN: Liver disease.

What?

JULIA BELLUZ: We now have tens of millions of people on these drugs, and they're reporting back to the researchers all these other benefits that they're discovering, reversals of long COVID, arthritis, post-concussion syndrome, lupus symptoms controlled, irritable bowel syndrome that kind of plagued some of the people I have talked to for decades, and they go on a GLP-1 drug and suddenly their symptoms disappear.

WILLIAM BRANGHAM: But there are drawbacks, and we're not just talking about their high price, which we will get to in a minute.

According to one study, up to three-quarters of people who start taking these drugs stop within a year.

And when they do, they often quickly regain whatever weight they have lost.

And the side effects of these drugs can be hard to ignore, including nausea, vomiting, and diarrhea.

While patients drop fat, some lose critical muscle mass as well.

There are even rare reports of eye damage leading to blindness.

Thousands of patients have already filed lawsuits against the drugmakers, alleging they failed to adequately warn about these risks.

But just how widespread these effects are still remains to be seen.

JULIA BELLUZ: Science really needs to catch up.

And we will, I think, make discoveries of great benefits that we don't yet know about, but we're also going to discover disappointments and we will discover harms, especially as the numbers grow.

And I think it could very well be that billions of people take these drugs.

I think we're just at the beginning of the great GLP-1 experiment.

WILLIAM BRANGHAM: So back to this other major issue with GLP-1s, their price.

As more and more people get on the drugs, many employers and insurers have moved to drop insurance coverage.

And, without insurance, patients are sometimes forced to spend over $1,000 a month.

DR.

MEHMET OZ, Administrator, Centers for Medicare and Medicaid Services: Reducing the cost, for example, of what the president calls the fat shot, The Ozempic GLP-1 category of medications.

We dropped them dramatically.

WILLIAM BRANGHAM: The government has launched programs and struck deals with pharmaceutical companies to bring the cost as low as $50 a month for some people, but access is uneven.

MAN: I was literally having to make the decision between taking care of my family or getting the medication.

WOMAN: For the quality of life change that I have had by being on this drug, to me, it's really worth going through any financial challenges.

WILLIAM BRANGHAM: But there are some other key underlying questions here.

Will spending on GLP-1s today prevent all sorts of chronic diseases and thus reduce the cost of treating those diseases down the road?

And what kind of economic and societal impacts will come from a global GLP-1 industry that by one estimate could reach $200 billion by 2030?

JULIA BELLUZ: It's a drug that seems to work across so many conditions.

It's a drug that helps people lose weight in a way that humans have desired for so long.

It's also a drug that is very visual in our kind of social media age where you can post your before-and-after picture.

And it's a drug in our telemedicine moment where the barriers to entry for getting pharmaceuticals now is quite low.

And so I don't think we have ever seen anything like this in the history of medicine.

WILLIAM BRANGHAM: In the coming days, we're going to explore some of these big outstanding questions, the challenge of providing equal access to GLP-1s, how they can be used to treat addiction, and what happens when such potent weight loss drugs are deployed in our looks-obsessed culture.

For the "PBS News Hour," I'm William Brangham.

And this is GLP-1s: Reshaping America.

GEOFF BENNETT: And, tomorrow night, Stephanie Sy will explore which Americans have access to GLP-1s and who continues to be priced out.