When Mark Basa needed his next dose of Wegovy, he worked his way down a list of 10 CVS stores within a 25-mile radius of his Peekskill, N.Y., home — and struck out at every one. In the 10 weeks he couldn’t find the drug, he regained the eight pounds he had lost on the medication, and his blood sugar rose. He felt himself get out of breath more often. His shirts fit tighter.

“It was anxiety-inducing,” Mr. Basa, 37, said. “It was like, ‘Well, I’m never going to lose this weight.’”

Wegovy has appeared on the Food and Drug Administration’s drug shortage list since March 2022. But doctors and patients say that the situation has worsened in the months since Novo Nordisk, the Danish company that manufactures the drug, limited the availability of the three lowest doses of Wegovy. With demand climbing faster than supply can keep up, the move effectively slows the pace of people starting the drug, because patients must begin with a low dose that is gradually increased. The shortage has fueled widespread frustration among potential patients, as well as those like Mr. Basa who need to refill their prescriptions or risk regaining weight.

“It’s created this living hell,” said Dr. Andrew Kraftson, a clinical associate professor in the division of metabolism, endocrinology and diabetes at Michigan Medicine.

A Novo Nordisk representative wrote in an email that the drugmaker anticipates “ongoing supply disruption” for those three doses as demand continues to outpace production. The company did not have an estimate for how long they will continue to limit those doses.

“The pipe is closed,” said Dr. Scott Hagan, an assistant professor of medicine at the University of Washington who studies obesity. Dr. Hagan sees patients with severe arthritis in need of hip and knee replacements who are above the body mass index threshold for surgery; Wegovy could help them lose enough weight to have surgery, he said, but not if they’re unable to start the drug.

Wegovy is an injectable version of a compound called semaglutide, which slows the emptying of the stomach and, in turn, makes people feel full faster and for longer. It also targets the areas of the brain that regulate appetite, reducing cravings and silencing what some people call “food noise.”

New patients start by injecting themselves weekly with the lowest dose of Wegovy for a month; after that, they can increase the dose monthly until they reach a “maintenance dose.”

When people stop taking Wegovy, they often regain weight. And when patients can only access the medication in fits and starts, they may end up “weight cycling,” a term researchers use to describe fluctuations in weight — which may increase the risk of cardiovascular disease.

Some patients end up temporarily taking older weight loss medications like Saxenda as a stopgap, but those alternatives are far less effective and can come with new side effects, Dr. Kraftson said. Others may end up trying to source semaglutide from compounding pharmacies, which can introduce a host of dangers and complications. Patients may want to switch to Ozempic, but that, too, can be hard to find.

Dr. Padmaja Akkireddy, an endocrinologist at Nebraska Medicine, said that when patients stop taking Wegovy for more than a month, she starts them back on a lower dose — which can be disappointing for people looking to lose more weight, and faster.

Others, like Ali Husain, have tried to find workarounds. Mr. Husain, 51, started the medication in March to cut down on weight he had gained earlier in the Covid-19 pandemic. By June, he was only able to find higher doses in stock. When his pharmacy accidentally sent him the highest dose after he spent weeks without the drug, he decided to measure his own lower doses. But after he resumed taking the medication and reached a higher dose, the side effects rattled Mr. Husain, who vomited so intensely that his stomach ached for days.

One reason that patients are advised to follow the strict dosing schedule is to stave off side effects.

“With a higher dose, there’s more weight loss, but also more side effects,” Dr. Hagan said. People can also experience more side effects if they go on and off the medication, Dr. Akkireddy said, because their bodies struggle to recalibrate.

Mr. Husain’s doctor decided to put him back on a lower dose to mitigate his side effects. Hours before he spoke with The New York Times, Mr. Husain received a text from Walgreens. It was out of stock.