Lilly’s weight-loss drug is a huge hit. Its CEO wants to replace it ASAP.

A deputy was calling with good news: The company’s new, experimental drug tirzepatide not only cut blood-sugar levels in people with diabetes in a small clinical trial, it also helped them lose much more weight than prior weight-loss drugs could achieve. The next step was a larger, expensive clinical study.

Looking out over the San Francisco Bay from the hilly campus of the University of California, Berkeley, Ricks sensed an opportunity.

“How fast can we go?" Ricks asked his deputy. “This is pedal-to-the-metal."

The decision to expedite the development of tirzepatide would transform Indianapolis-based Lilly. The drug hit the market in 2022 as Mounjaro for Type 2 diabetes and in 2023 as Zepbound for obesity. Together, they generated more than $5 billion in revenue last year and are on the way to becoming some of the bestselling pharmaceuticals of all time, along with rival Novo Nordisk’s Ozempic, which works similarly. In the process, Lilly’s valuation soared past $750 billion, making it the world’s largest drugmaker by market cap.

The success of the drugs validated one of Ricks’ top priorities: speed. “We want to be first and best," he said in an interview with The Journal podcast. “Our saying is, ‘The patient is waiting.’"

The question is whether Ricks can keep Lilly at pace. Today many patients are waiting for Mounjaro and Zebpound; demand for the drugs is so overwhelming that there’s an ongoing shortage, and Lilly is hustling to produce more of the medications. At the same time, the company is under pressure to develop an even more potent anti-obesity drug as competition mounts from rivals old and new.

An Eagle Scout who loves the outdoors, Ricks, 57, has long understood that acting fast is essential to survival—both at work and in the wild. Once, while backpacking with his father, the two had to scramble to escape a black bear that went after their food. They were forced to fish in the river for meals for the rest of the weeklong trip.

“I’ve learned a few tips along the way that apply both in backpacking and the boardroom," Ricks wrote in a 2018 blog post describing the incident. Among them was, “Once you know there’s a problem, delay only increases the danger."

That principle has stayed with Ricks on his rise up the ranks at Eli Lilly, where he has worked for 28 years. Ricks, who has an undergraduate degree from Purdue University, had a brief stint at IBM in the early 1990s before getting an M.B.A. from Indiana University and then joining Lilly as a business-development associate.

Though he lacked scientific training, Ricks showed he could learn the science quickly. “He soaked it up," said J. Anthony Ware, who led product development at Lilly before retiring in 2017.

Besides being a quick study, Ricks was a good communicator who was willing to give credit to colleagues. Company executives noticed. “We could see an early maturity and an ability to work with people," former Lilly CEO Sidney Taurel said of Ricks. “So we decided to put him on the fast track."

Not that Ricks’ emphasis on speed was always well-received. Sometimes it came off as restless. His predecessor, John Lechleiter, once told Ricks during an annual performance evaluation that he had “an overdeveloped sense of urgency" and suggested that he slow down, Ricks told the Indianapolis Business Journal.

“I thought that was an interesting turn of phrase, meaning that I’m very impatient," Ricks told the paper. “And that’s certainly true; you can ask my wife. I’ve got a high motor."

When he took over the top job in 2017, Ricks’ agility in decision-making served him well. At the time, Lilly was bouncing back from a series of patent losses and drug-research failures. It was also reeling from a bitter disappointment: The company had been banking big on an experimental Alzheimer’s drug that failed its late-stage, or Phase 3, trial.

Ricks assured investors that Lilly had more in the works beyond Alzheimer’s.

One core engine for growth, he said, would be diabetes treatment. Lilly’s past is deeply tied to diabetes, having been the first company to sell insulin after it licensed a patent from the University of Toronto a century ago. In 2017, the company was investing in a promising new category: glucagon-like peptide-1 receptor agonists. GLP-1 drugs mimic a natural hormone to control blood-sugar, and, as researchers increasingly realized, could also help people lose weight by suppressing appetite.

Back in Lilly labs, researchers were working on tirzepatide. The drug threatened to cannibalize sales of another Lilly diabetes drug called Trulicity, which was racking up big sales. But Ricks didn’t care. This was a race he couldn’t lose. Rival Novo Nordisk was already ahead. Its diabetes drug Ozempic was already on the market and its main ingredient was being tested for weight loss.

Lilly put the larger clinical studies for tirzepatide on an accelerated timeline, and Mounjaro hit pharmacy shelves two years ahead of schedule—a huge time savings in an industry known for yearslong development cycles. Just a year and a half later, it was approved as Zepbound for chronic weight management.

“I’m pretty sure at this later stage in my career that I’ll never work on a more important medicine than tirzepatide," Ricks said. “I’m super proud of that."

The follow-on health benefits from patients losing weight are rippling across industries. Diet and exercise companies, such as Weight Watchers, have called Ricks seeking advice on how they can win in a market where GLP-1 drugs are booming. He’s also fielded calls from corporate leaders who have questions about these drugs’ impact on their businesses.

“Of course we talked to Walmart and all our big food stores," Ricks said. Last year, Walmart CEO Doug McMillon told Bloomberg News that shoppers who picked up prescriptions for GLP-1 drugs at Walmart pharmacies were putting less food in their grocery baskets.

Ricks advises the affected companies to adapt to a world where fewer consumers are obese. “If you make knee replacements? That’s not great. But I’m sure there’s other health problems they can go work on and make devices for," he said. “We will directly displace those things. That’s not our strategy, but we are trying to make it better and easier to live with those conditions by losing weight."

Likewise, Ricks says foodmakers will need to adjust. “If they’re worried about salty snack foods high in fat, saturated fat, or selling less? I’d say, ‘Well, why don’t you make healthier ones?’ " he said.

The drug’s success has spawned new challenges for Lilly, too. One is that Lilly can’t make enough to satisfy heavy demand for Mounjaro and Zepbound, which come in injectable pens. Lilly is investing billions of dollars to build more capacity. But the process of getting plants built, making sure they work properly, and having regulators approve them, is testing his patience.

“We’re all building everything as fast as we can," he said. “The bad news is that it takes three or four years to build a new plant, to get it running safely, prove it’s effective…and do it at scale. It takes a long time."

A potential avenue for relief is to make a GLP-1 drug in pill form. Lilly has one in the pipeline called orforglipron. Unlike injectables, oral drugs can be manufactured more swiftly. “We have many, many oral drugs in the world," Ricks said. “Those production systems are already built. And so we can partner and buy capacity quite quickly."

But it’s not easy to turn these types of medicines into a pill. GLP-1 drugs like tirzepatide are large, complex molecules. Some early efforts at other drugmakers to make anti-obesity pills have already failed. Lilly has to finish large clinical trials to prove its pill candidate’s efficacy and safety, and then get regulatory approval, before it can start selling it, a process likely to take another year or two.

Ricks is determined to avoid the mistake that the company made with a blockbuster drug decades earlier: the antidepressant Prozac.

Like this class of GLP-1 medications, Prozac was hailed as a so-called wonder drug. It quickly racked up $3 billion of annual revenue by the late 1990s and made the leap from the realm of medicine into that of culture. A bestselling memoir of depression in the 1990s was called Prozac Nation and later made into a movie with the same title. But Lilly failed to keep investing in the science. When the Prozac patent lapsed in 2001, Lilly didn’t have a successor ready to launch for another couple of years and was caught flat-footed as generics ate up its revenue. Further antidepressant research fizzled out.

Ricks has high hopes for a new drug his scientists are working on called retatrutide. It’s a triple-agonist drug—so called because it mimics three appetite-suppressing hormones.

Retatrutide, Ricks said, “has a strong effect on visceral fat and liver obesity and other really difficult-to-treat types of obesity. As a result, you lose even more weight than tirzepatide."

Retatrutide is still in Phase 3 trials and won’t be up for FDA approval for a few years. If it succeeds in testing, it would escalate the race for even more potent drugs to target obesity.

Thus far the sprint has been as fast as drug development can be, mainly between Lilly and Novo Nordisk. More companies, like Pfizer, Amgen and Roche, are now in the mix as well.

Lilly scientists have about half a dozen other obesity projects in the works. “Some of them will work, some of them won’t," Ricks said. “But I think we really see diseases becoming tractable and fixed in a broad way when we have many ways to attack them. And we’re investing heavily in that." Last year, Lilly acquired a company developing a drug designed to preserve muscle mass during weight loss—potentially addressing a concern about the loss of lean muscle mass that some people on the current crop of drugs may experience.

“Lilly’s got a lead," he added, “and we plan to exploit that lead."

To listen to “Trillion Dollar Shot," a four-part podcast series from The Journal about how a new class of drugs used for weight loss is transforming bodies, fortunes and industries, click here or look for it on your favorite podcast player. You can also find the full series on Spotify.

Write to Jessica Mendoza at jessica.mendoza@wsj.com, Matt Kwong at matt.kwong@wsj.com and Peter Loftus at Peter.Loftus@wsj.com