Ozempic and Weight Loss Drugs: Which Should You Choose?

People with obesity now have a choice between two powerful drugs to help them lose weight. One is semaglutide, sold by Novo Nordisk as Wegovy for obesity treatment and as Ozempic for diabetes. The second, tirzepatide, is sold by Eli Lilly as Zepbound for obesity and as Mounjaro for diabetes. Many with neither obesity or diabetes take the drugs to get thinner.

A recent study suggested that people lost more weight taking Mounjaro than they did taking Ozempic, and it may leave you wondering: Which should I take? And if I’m already taking one of them, should I switch?

The answers, obesity medicine experts say, are not so simple. Here are some factors that can help sort out hype from realistic hope.

Is one weight loss drug really better than the other?

For now, it’s hard to say. All of the information available comes from “highly flawed studies,” said Dr. Diana Thiara, medical director of the weight loss clinic at the University of California, San Francisco.

That includes the recent study comparing Mounjaro and Ozempic. Using electronic health records, the researchers reported that those taking Mounjaro lost an average of 15.3 percent of their weight after a year. Those taking Ozempic lost an average of 8.3 percent.

While that sounds impressive, Dr. Susan Z. Yanovski, co-director of the Office of Obesity Research at the National Institute of Diabetes and Digestive and Kidney Diseases, said, “I wouldn’t make any decisions on my medical care based solely on a study like this.”

There’s an inherent difficulty in using electronic health records, she noted, because it is not known why the patients were taking the drugs — the study was done before Wegovy and Zepbound were approved for treating obesity. The drugs on the market, Ozempic and Mounjaro, were approved to treat diabetes. Yet many in the study did not have diabetes.

The researchers also did not know the doses — they knew only that a prescription was filled. That’s a problem because the drugs can be prescribed in different doses, which “may lead to different weight loss outcomes,” noted Tricia Rodriguez, a senior applied scientist at Truveta Research and the lead researcher for the comparison study.

And, Dr. Yanovski observed, fewer than half the patients were still taking the drugs by the end of the study.

It’s also true that clinical trials for the drugs showed differences in weight loss. Novo Nordisk reported that participants taking Wegovy lost 14.9 percent of their body weight after 68 weeks. For Zepbound, Eli Lilly said participants lost 20.9 percent after 72 weeks on a 15-milligram dose. But those were not head-to-head studies in which the drugs were tested against each other, making it difficult to compare results.

Future research should give better answers: Eli Lilly is conducting a clinical trial comparing Zepbound to Wegovy in people with obesity who do not have diabetes. It is expected to be completed later this year.

Why did my doctor pick one drug over the other?

It might depend on your health insurance. Some insurers will pay for one but not the other, Dr. Thiara said. Others, she added, will insist that patients start with Wegovy and will only pay for Zepbound if they fail to lose weight or if the side effects are intolerable.

She has prescribed both to patients but says her choice often is determined by the patient’s insurance.

“Insurance companies dictate so much of what we can do,” Dr. Thiara said.

Or your doctor might be being cautious. Wegovy has been around longer, Dr. Yanovski noted.

Another consideration might be other medical conditions the drugs could help with.

Semaglutide reduces the risk for cardiovascular disease. That has not yet been shown for tirzepatide. The drug also reduces complications in people with kidney disease. Novo Nordisk found in another clinical trial that Wegovy improved physical functioning — like an ability to exercise — in people with obesity and heart failure.

On the other hand, Eli Lilly found that Zepbound could help with sleep apnea. Patients who took the drug also had significantly lower blood pressure.

A variety of clinical trials are testing the effects of semaglutide and tirzepatide on even more diseases: cancer, arthritis and even Alzheimer’s.

What if I want to switch drugs to lose more weight?

If you are doing well with Wegovy and your health has improved, you might want to stay with it, said Dr. Rudolph Leibel, a diabetes and obesity researcher at Columbia University Irving Medical Center. It’s not clear that switching to Zepbound would be better.

“On the flip side,” Dr. Leibel said, “there clearly are people who do not respond well to semaglutide and may benefit from switching to tirzepatide.”

But it is virtually impossible to predict who is going to be the most responsive to one of these drugs, he said, and who will experience the fewest side effects.

Your health is also an issue.

If a patient is healthier after starting on Wegovy, with changes like lower blood pressure and a reduction of the amount of fat and inflammation in the liver, for example, that is an argument for staying on the drug, Dr. Yanovski said.

Of course, Dr. Thiara said, many patients want to lose as much weight as they can — many have struggled with obesity and its stigma for years and just want it to end. If switching to Zepbound will help them lose more weight, they want to do it.

Dr. Thiara sayid she emphasized goals with her patients — the goal is to be healthy, “not to be a size 2.”

“If their goal is to look a certain way, there is only so much I can do,” she added.

Are there downsides to switching?

When patients start on an obesity drug, their doctors usually prescribe a low dose and then increase it. The goal is to minimize side effects like nausea and vomiting.

There’s no data to say that switching from one drug to another at a higher dose could lead to problems, obesity medicine experts say. But many doctors are cautious, and want to give patients at least a month at the lowest dose with the new drug to see how well it is tolerated.

When switching to a lower dose, though, you probably will regain some weight.

Another consideration is whether you may have an easier time getting one drug than another. Because demand is so high and production cannot keep up, both drugs can be difficult to get, and their availability “ping pongs back and forth,” Dr. Thiara noted.

Are additional weight loss drugs coming in the future?

Drugs in development promise to be even more powerful in eliciting weight loss than the two on the market. Economists expect that with more drugs, prices will fall and supply constraints will ease.

Doctors expect that the decision of which drug to prescribe will become even more complex.

But that is a good problem, Dr. Leibel said, adding that it reminded him of the evolution of drugs for high blood pressure. In the early days there were only a few, and they were less effective with more side effects than the dozens of blood pressure drugs today. Now most patients can find a drug or drug combination to control their blood pressure with no or minimal side effects.

Obesity drugs, he predicted, are on a similar path.

“This is a novel inflection point in the history of the treatment of obesity,” Dr. Leibel said.