Ozempic vs. Mounjaro: How Do They Compare?
Scripps weight-loss expert explains how they work
Scripps weight-loss expert explains how they work
An increasingly popular class of prescription drugs known as GLP-1s, including Ozempic and Mounjaro, has become a popular option among people seeking to lose a significant amount of weight.
In fact, according to a poll, 1 in 8 adults (12%) in the United States have taken a GLP-1 medicine at some point in their life, either for weight loss, to treat diabetes or to reduce the risk of heart diease and stroke. This includes 6% of adults who say they are currently taking one of these drugs, which include Ozempic, Wegovy and Mounjaro.
But are these drugs equally effective for weight loss? In a recent study published in JAMA Internal Medicine, researchers compared Ozempic and Mounjaro in real-world conditions and found that people who took Mounjaro lost significantly more weight than those who took Ozempic. Moreover, the longer the patients kept taking the drugs, the wider the gap became.
How are they different?
Mounjaro and Ozempic, originally developed to manage type 2 diabetes, contain active ingredients tirzepatide and semaglutide, respectively. Tirzepatide is also marketed by Eli Lilly as Zepbound, while semaglutide is available as Wegovy by Novo Nordisk, both targeting weight loss. These drugs belong to the GLP-1 class, which mimic the hormone glucagon-like peptide 1 (GLP-1) to increase insulin production, slow digestion, reduce appetite and extend feelings of fullness. Mounjaro also mimics a second hormone, GIP, further enhancing satiety.
While this additional hormone may be one reason Mounjaro caused greater weight loss in the study, Ken Fujioka, MD, an endocrinologist and director of the Scripps Clinic Nutrition and Metabolic Research Center, believes several factors may have impacted the results.
“I would agree that in this study Mounjaro has on average more weight loss than Ozempic. I would expect this as you have two satiety hormones versus one,” says Dr. Fujioka, who was not involved in the study.
However, he adds, another reason that this study showed more weight loss with Mounjaro was the dose of Ozempic used. On March 28, 2022, Ozempic was approved by the FDA for 2 mgs weekly. Many prescribers were not aware of this and were ordering lower doses, according to Dr. Fujioka.
“The timing of this study was challenging because Ozempic had just been approved for the higher dose, which definitely gives more weight loss. The dose in this study is low for Ozempic,” he says. “I still agree that Mounjaro is more potent than Ozempic, but I’m just not sure how much.”
How well do these drugs work for people with diabetes?
When researchers compared patients in the study with and without type 2 diabetes, they found that those who didn’t have diabetes lost more weight than those who did — regardless of which drug they took. Dr. Fujioka says this has been the case for a long time, although no one knows exactly why.
“Some of the medications that people with diabetes take make it more difficult to lose weight,” he explains. “Another reason is probably genetics. Individuals who have the genetics to become diabetic probably have the genetics to gain weight and hold on to it better. I suspect some leftover survival gene set that some folks are just unlucky enough to inherit.”
Similarly, the study found no significant differences in adverse events between the two drugs, despite the differences in the amount of weight lost. Dr. Fujioka says this is not surprising, since both are satiety hormones with similar target receptors. Moreover, both Ozempic and Mounjaro were used at lower doses in the study; adverse events tend to increase with dose.
Should patients switch?
Dr. Fujioka says there is probably no reason for a physician to prescribe Mounjaro instead of Ozempic, or for a patient taking Ozempic to switch to the other drug. He routinely prescribes both.
“It all comes down to what their insurance will cover. The biggest reason patients stop taking meds is that insurance will no longer cover the medication,” he says. “Also, many times, the side effects of one drug are not tolerated by the patient and then I will switch them to the other.”
In addition, supply issues that affect the availability of a specific medication — which were a factor when this study was done — can determine which one will be prescribed.
“My main concern about this study was the low dose given for both medications,” says Dr. Fujioka. “If the medication is doing its job and is dosed appropriately, I would see no reason to switch and would recommend against it.”
Learn more about weight-loss drugs
Watch the San Diego Health video or listen to the podcast on who is the right candidate for weight-loss drugs.