Obese people now have a choice of two powerful drugs to help them lose weight. The first is semaglutide, sold by Novo Nordisk as Wegovy for obesity and as Ozempic for diabetes. The second, tirzepatide, is sold by Eli Lilly as Zepbound for obesity and as Mounjaro for diabetes. Many people who are neither obese nor diabetic take these drugs to lose weight.
A recent study showed that people lost more weight taking Mounjaro than taking Ozempic, and you may be wondering: Which one should I take? And if I’m already taking one, should I switch?
The answers aren’t so simple, according to obesity medicine experts. Here are some factors that can help differentiate between hype and realistic hope.
Is one weight loss drug really better than another?
It’s hard to say for now. All the information available comes from “very flawed studies,” said Dr. Diana Thiara, medical director of the University of California, San Francisco’s Weight Loss Clinic.
This includes the recent study comparing Mounjaro and Ozempic. Using electronic medical records, researchers reported that people taking Mounjaro lost an average of 15.3% of their weight after one year. Those taking Ozempic lost an average of 8.3% of their weight.
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 about my medical care based solely on a study like this.”
One problem with using electronic medical records, she said, is that it’s unclear why patients were taking the drugs. The study was conducted before Wegovy and Zepbound were approved to treat obesity. The drugs on the market, Ozempic and Mounjaro, were approved to treat diabetes. Yet many of the study participants did not have diabetes.
The researchers also didn’t know the doses, only that a prescription had been issued. That’s a problem because drugs can be prescribed at different doses, which “can lead to different weight-loss outcomes,” noted Tricia Rodriguez, a senior applied scientist at Truveta Research and lead researcher on the comparative study.
And, as Dr. Yanovski observed, less than half of the patients were still taking the drugs at the end of the study.
It’s also true that clinical trials of the drugs have shown differences in weight loss. Novo Nordisk reported that participants taking Wegovy lost 14.9% of their body weight after 68 weeks. For Zepbound, Eli Lilly said participants lost 20.9% of their body weight after 72 weeks with a 15-milligram dose. But these weren’t head-to-head studies in which the drugs were tested against each other, making it difficult to compare the results.
Future research should provide better answers: Eli Lilly is conducting a clinical trial comparing Zepbound to Wegovy in obese people who don’t have diabetes. It’s expected to be completed later this year.
Why did my doctor choose one medication over another?
It depends on your health insurance. Some will cover one drug 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 drugs to her patients, but says her choice is often determined by the patient’s insurance.
“Insurance companies dictate a lot of what we can do,” Dr. Thiara said.
Or maybe your doctor is being cautious. Wegovy has been around longer, Dr. Yanovski noted.
Another consideration might be other medical problems that medications might help with.
Semaglutide reduces the risk of cardiovascular disease. This 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 – such as the 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 taking the drug also had significantly lower blood pressure.
Various clinical trials are testing the effects of semaglutide and tirzepatide on even more diseases: cancer, arthritis and even Alzheimer’s disease.
What if I want to change medications to lose more weight?
If you feel good with Wegovy and your health has improved, you may want to keep using it, said Dr. Rudolph Leibel, a diabetes and obesity researcher at Columbia University Irving Medical Center. It’s not clear that switching to Zepbound is a better option.
“On the other hand,” Dr. Leibel said, “there are clearly people who don’t respond well to semaglutide and who might benefit from a switch to tirzepatide.”
But it’s virtually impossible to predict who will respond best to any 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 Wegovy, with changes like lower blood pressure and reduced fat and inflammation in the liver, for example, that’s an argument for continuing to take the drug, Dr. Yanovski said.
Of course, Dr. Thiara said, many patients want to lose as much weight as possible. Many have struggled with obesity and the stigma that comes with it for years and simply want it to stop. If switching to Zepbound helps them lose more weight, they want to do it.
Dr. Thiara said she emphasizes 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’s not much I can do,” she added.
Are there any downsides to switching?
When patients start taking an obesity medication, their doctor usually prescribes a low dose and then increases it. The goal is to minimize side effects such as nausea and vomiting.
Obesity medicine experts say there is no data to suggest that switching from one drug to a higher dose could cause problems. But many doctors are cautious and want to give patients at least a month on the lower dose of the new drug to see if it is tolerated.
However, if you switch to a lower dose, you will likely regain the weight.
Another question is whether one drug is more readily available than the other. With demand so high and production unable to keep up, both drugs can be difficult to obtain, and their availability “fluctuates from one drug to the other,” Dr. Thiara noted.
Will other weight loss drugs be available in the future?
The drugs under development promise to be even more effective at causing weight loss than the two drugs already on the market. Economists expect that more drugs will become available, leading to lower prices and less supply constraints.
Doctors expect the choice of which drug to prescribe to become even more complex.
But it’s a positive problem, Dr. Leibel said, adding that it reminds him of the evolution of blood pressure medications. In the beginning, there were only a few, and they were less effective and caused more side effects than the dozens of current blood pressure medications. Today, most patients can find a drug or combination of drugs to control their blood pressure with no or minimal side effects.
Obesity drugs, he predicts, are following a similar path.
“This is a new turning point in the history of obesity treatment,” Dr. Leibel said.