What's better for weight loss, Mounjaro or Ozempic? New study provides answer

As the popularity of drugs used for weight loss continues to explode, a new study is shedding light on which drug is most effective for weight loss.

Mounjaro, a drug with the main active ingredient tirzepatide, was found to be more helpful in helping people lose weight and maintain their weight loss, according to a study published Monday in JAMA Internal Medicine.

Individuals taking Mounjaro were three times as likely to lose 15% or more of total body weight, 2.5 times as likely to experience 10% or more weight loss, and 1.8 times as likely to experience 5% or more weight loss compared to those taking semaglutide, the active ingredient found in Ozempic.

This finding was sustained at 12 months of follow-up, according to the study, which analyzed more than 18,000 patients with obesity, both with and without Type 2 diabetes.

The study found that patients without diabetes lost more weight than patients with diabetes.

According to the study's authors, more research is needed to understand why Mounjaro, with the active ingredient tirzepatide, was found to be more effective for weight loss.

Tirzepatide targets both the GLP 1 and the GIP receptor agonist, while semaglutide mimics only the GLP-1 receptor agonist, a type of hormone in the body that impacts everything from the brain to muscle to the pancreas, stomach and liver.

Both Ozempic and Mounjaro are approved by the U.S. Food and Drug Administration to treat Type 2 diabetes, but some doctors prescribe the medication "off-label" for weight loss, as is permissible by the FDA.

When these drugs are used "off-label," it is usually not covered by insurance and can be costly, running as much as $1,000 per month.

There are also now two drugs on the market that are FDA-approved for weight loss -- Wegovy, a medication that contains the same main ingredient, semaglutide, as Ozempic, and Zepbound, a medication that contains the same main ingredient, tirzepatide, as Mounjaro.

The drugs, typically taken once weekly as injections, work by helping the pancreas increase the production of insulin to move sugar from the blood into body tissues.

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They also slow down the movement of food through the stomach and curb appetite, thereby causing weight loss.

Past clinical studies have shown users of the medications can lose between 5% and 20% of their body weight on the medications over time.

Medical specialists point out that using medication to lose weight also requires cardio and strength training and changing your diet to one that includes proteins and less processed foods with added sugars.

The most commonly reported side effects of medications used for weight loss are nausea and constipation, but gallbladder and pancreatic disease are also reported. Makers of these drugs recommend having a conversation about the side effect profile and personalized risks with a healthcare professional before starting.

The study found there was no difference in the number of adverse gastrointestinal effects between people with and without Type 2 diabetes in the study.

Prapti Chatterjee-Murphy, M.D., a member of the ABC News Medical Unit, contributed to this report.