The world of weight loss treatment is seemingly expanding by the day. With each passing year, more and more weight loss options are getting approved by the Food and Drug Administration (FDA), bringing new hope and opportunity for patients struggling with their weight.

You’ve likely heard about some of the common weight loss medications, like Ozempic, Wegovy, Mounjaro, and Zepbound, but perhaps you are unaware how each of these medications differs. Knowing the key differences and similarities between weight loss medications is essential to making informed decisions about your health. Thus, we will review two popular drugs, Ozempic and Mounjaro, to elucidate their similarities and differences.

Mechanism

The main way that Mounjaro and Ozempic differ is with regard to their mechanism. Ozempic contains the active ingredient semaglutide, which is a glucagon-like peptide-1 (GLP-1) receptor agonist. As a GLP-1, semaglutide elicits therapeutic action in two ways. First, it activates the release of insulin from the pancreas, helping to control blood sugar levels, and explaining why semaglutide is also approved for the treatment of diabetes. Secondly, semaglutide delays a process known as gastric emptying. In doing so, the speed at which food moves through your body decreases, causing you to feel fuller for longer periods of time. Via this mechanism, GLP-1s are effective in weight loss.

Mounjaro, on the other hand, contains the active ingredient known as tirzepatide. Tirzepatide is very similar to semaglutide, as it also acts as a GLP-1 agonist, thus lowering blood sugar levels and supporting weight management. However, Mounjaro has an additional mechanism as a glucose-dependent insulinotropic polypeptide (GIP) receptor agonist. This additional activity makes it a bit more efficacious in the weight loss realm, which will be discussed later in this article.

Indication

It is also important to note how all these weight loss medications differ with regards to their FDA-approved indication. When it comes to Ozempic and Mounjaro, the indications for the two are the same: treatment of type 2 diabetes mellitus to improve blood sugar levels as an adjunct to diet and exercise.

Recall that Ozempic contains semaglutide and Mounjaro contains tirzepatide. Although semaglutide and tirzepatide are approved under brand names Ozempic and Mounjaro for type 2 diabetes, they are also approved under separate brand names specifically for weight management. Semaglutide is available under the brand name Wegovy, and tirzepatide is available under the brand name Zepbound. Wegovy and Zepbound are both approved for chronic weight management in obese or overweight individuals with at least one weight-related issue.

Although Ozempic and Mounjaro are approved for type 2 diabetes, they are oftentimes prescribed “off-label” by healthcare providers. This is a legal practice in which healthcare professionals can prescribe a medication for a use not approved by FDA. For example, a physician may prescribe Ozempic for weight loss as opposed to diabetes.

Dosing

Both medications are relatively similar with regards to dosing. Both are available as a single-dose injectable pen, which should be administered once weekly. The medications can be injected into the same spots (thigh, abdomen, or upper arm), with careful dose titration over the course of several weeks.

Because the medications contain different active ingredients, the actual doses are different. Typical dosing is as follows:

  • Ozempic: Begin at a starting dose of 0.25 mg once weekly. After four weeks, the dose can be increased to 0.5 mg once weekly. If further glycemic control is required, the dose can be increased once more to 1 mg once weekly after an additional four weeks.
  • Mounjaro: Begin at a starting dose of 2.5 mg once weekly. After four weeks, the dose can be increased to 5 mg once weekly. If further glycemic control is required, the dose can be increased in 2.5 mg increments every four weeks to a maximum dose of 15 mg weekly.

Effectiveness in weight management

When it comes to weight loss, both semaglutide and tirzepatide have been studied for this purpose. Let’s review the data supporting the two drugs for this indication.

Tirzepatide

Tirzepatide was evaluated in two large clinical studies to determine its effects on weight loss as an adjunct to diet and exercise. The studies measured weight loss over 72 weeks in more than 3,500 patients who were randomized to get either tirzepatide 5, 10, or 15 mg or a placebo.

The trial outcome showed that after 72 weeks, tirzepatide 5, 10, and 15 mg induced statistically significant reductions in body weight versus those on placebo. More individuals taking tirzepatide lost a minimum of five percent of their baseline body weight versus individuals taking a placebo.

The two studies evaluated different patient populations, one with diabetes and one without. In the study with diabetic patients, subjects on 15 mg of tirzepatide lost an average of 12 percent of their weight. In the study with non-diabetic patients, subjects lost an average of 18 percent of their weight.

Semaglutide

Investigators have studied semaglutide for weight loss in a panel of studies known as the STEP trials. The findings of the first few STEP trials concerning weight are as follows:

  • STEP 1: Semaglutide 2.4 mg caused a 14.9 percent reduction in body weight versus a reduction of 2.4 percent with a placebo
  • STEP 2: Weight decreases were 9.64, 6.99, and 3.42 percent with semaglutide 2.4 mg, semaglutide 1.0 mg, and placebo, respectively
  • STEP 3: Semaglutide 2.4 mg caused 16.0 percent reductions in weight versus 5.7 percent with placebo, each in combination with behavioral therapy
  • STEP 4: Individuals staying on semaglutide had total reductions of 17.4 percent while those switching from semaglutide back to placebo regained 6.9 percent of their weight

There have been many more STEP trials in addition to these that further substantiate semaglutide’s efficacy in lowering body weight. Additionally, there are even more STEP studies that are currently active and ongoing.

Comparing efficacy

When comparing the data between tirzepatide and semaglutide in weight loss, studies show that tirzepatide may be a bit more efficacious when it comes to decreasing body weight. This could be due to its dual mechanism as a GLP-1 and GIP receptor agonist, as semaglutide is solely a GLP-1 receptor agonist.

Safety

There is quite a bit of overlap concerning the side effects of both medications. Because both medications are GLP-1 agonists, they both have activity in delaying gastric emptying. This can inherently cause side effects related to the gastrointestinal (GI) tract. Typically, these side effects will resolve over time and can be minimized by slowly increasing one’s dose.

Common side effects of both medications are included in the table below.

OzempicMounjaro
  • Nausea
  • Vomiting
  • Diarrhea
  • Constipation
  • Abdominal pain
  • Nausea
  • Vomiting
  • Diarrhea
  • Constipation
  • Abdominal pain
  • Decreased appetite
  • Indigestion

Comparing Mounjaro and Ozempic

To summarize, key similarities and differences between Mounjaro and Ozempic are outlined below.

MounjaroOzempic
Active ingredientTirzepatideSemaglutide
FDA-approved indicationControl blood sugar in patients with type 2 diabetes mellitus adjunct to diet and exerciseControl blood sugar in patients with type 2 diabetes mellitus adjunct to diet and exercise
AgesAdultsAdults
MechanismGIP and GLP-1 receptor agonistGLP-1 receptor agonist
AdministrationSingle dose pen

Injection under the skin into the abdomen, upper arm, or thigh once weekly

Single dose pen

Injection under the skin into the abdomen, upper arm, or thigh once weekly

DosingStarting dose of 2.5 mg once weekly. After four weeks, the dose can be increased to 5 mg once weekly. If further glycemic control is required, the dose can be increased in 2.5 mg increments every four weeks to a maximum dose of 15 mg weekly.Starting dose of 0.25 mg once weekly. After four weeks, the dose can be increased to 0.5 mg once weekly. If further glycemic control is required, the dose can be increased once more to 1 mg once weekly after an additional four weeks.
Mild side effectsNausea, vomiting, diarrhea, constipation, abdominal pain, decreased appetite, indigestionNausea, vomiting, diarrhea, constipation, abdominal pain
Serious adverse effectsPancreatitis, very low blood sugar, allergic reactions, kidney injury, serious GI disease, gallbladder disease, complications of diabetic retinopathyPancreatitis, very low blood sugar, allergic reactions, kidney injury, complications of diabetic retinopathy
Price without insurance~$1,000-$2,000~$1,000
EfficacyTirzepatide was evaluated in two, double-blind, randomized, placebo-controlled studies, which found tirzepatide was superior compared with placebo in terms of weight loss.Semaglutide is superior to placebo with regards to weight loss as demonstrated in the STEP trials.

Using this comparative table, you can see that there aren’t many differences Ozempic and Mounjaro. Key differences include:

  • Mechanism of action. Mounjaro demonstrates activity at both the GIP and GLP-1 receptors, while Ozempic is only active at the GLP-1 receptor.
  • Cost. Out of pocket, Ozempic is a bit cheaper than Mounjaro. However, the exact cost is dependent on one’s insurance coverage and pharmacy.
  • Effectiveness. Trials have demonstrated that Mounjaro may be more efficacious than Ozempic. However, every patient is different, so efficacy may vary from person to person.