Ozempic, Mounjaro and the new science of weight loss

There was a time when losing weight was largely associated with restrictive diets, endless workouts and the familiar promise of “eat less, move more.” Then came a new generation of medications that changed the conversation completely.

From Ozempic and Mounjaro to Victoza, Saxenda and Trulicity, injectable medications have moved from the doctor's office into everyday conversations, social media feeds and, for some, beauty and lifestyle trends. But behind the hype is a class of medications that has changed how doctors approach obesity and metabolic disease.

According to Mona Nasrallah, MD, Professor of Clinical Medicine in the Division of Endocrinology and Metabolism at the American University of Beirut, their popularity is not simply the result of clever marketing or a celebrity trend. It is also because, medically, they are producing results.

So, what exactly are these medications?

Most of the medications in this group are GLP-1 receptor agonists. Mounjaro (tirzepatide), however, is different: it acts on both GLP-1 and GIP pathways, making it a dual GLP-1/GIP agonist. “For the first time, we are able to see real results in the management of obesity,” Dr. Nasrallah explains, adding that these medications generally have tolerable side effects while also offering important metabolic benefits.

So how do they work?

It is not simply that they “burn fat.” Their effects are more complicated. They slow the emptying of the stomach, meaning food remains there for longer and can create a prolonged feeling of fullness. They also affect the pancreas, stimulating insulin release in a glucose-dependent manner and reducing the release of glucagon, helping improve blood-sugar control, particularly in people with diabetes.

And there is another important player: the brain. These medications can reduce appetite, making it easier for patients to eat less rather than constantly fighting hunger.

Who actually needs them?

This is where the conversation becomes particularly important. The fact that these medications can produce significant weight loss does not mean they are designed for anyone who wants to drop a few kilos.

Dr. Nasrallah says the main medical indications include adults with type 2 diabetes who are overweight or obese, as well as people with obesity or, in certain circumstances, overweight who have been unable to lose weight and have, or are at risk of developing, complications related to excess weight.

There are also specific medical indications beyond diabetes and obesity, including conditions such as obstructive sleep apnea and fatty liver disease. But wanting to look thinner is not, by itself, a medical indication. “They are not indicated medically for just cosmetic appearance,” Dr. Nasrallah emphasizes. That distinction matters at a time when weight-loss injections can sometimes be treated almost like another beauty product.

Beyond the number on the scale

The potential benefits go beyond fitting into a smaller pair of jeans. According to Dr. Nasrallah, these medications can improve blood glucose, cholesterol, triglyceride levels and the overall lipid profile. They can also improve insulin resistance and blood-pressure control.

There is also growing evidence of benefits involving cardiovascular health and the progression of kidney disease. In other words, medically supervised weight loss can be about much more than appearance. For the right patient, it can be part of managing a broader metabolic condition.

But they are still medications…

And that means they should not be treated casually. The most common side effects involve the digestive system, including nausea and vomiting. More serious complications can occur, including gallbladder problems and, rarely, inflammation of the pancreas.

Dr. Nasrallah also points to other issues doctors may need to assess, including retinal changes in certain patients and thyroid abnormalities. There is a possible association with a particular type of thyroid cancer, medullary thyroid cancer, which is why appropriate medical assessment is important before and during treatment. This is precisely why taking these medications without medical supervision can be risky.

What Happens When You Stop? 

Perhaps the most important question is not how quickly someone loses weight but what happens afterward. According to Dr. Nasrallah, weight regain after stopping these medications is commonly observed, particularly when they are stopped abruptly.

For this reason, she describes treatment as something that may need to be chronic rather than a quick fix. If treatment is discontinued, it should generally be done gradually and under medical supervision.

Losing weight is not simply about making the number on the scale go down. Poorly managed weight loss can also reduce lean body mass, including muscle and bone. Dr. Nasrallah emphasizes that these medications should therefore be accompanied by proper nutrition, adequate protein and calcium, physical activity and sufficient sleep. The injections can support a healthier lifestyle, but they are not a replacement for it. 

The reality behind the hype

The Ozempic and Mounjaro phenomenon may have started as a social-media sensation, but the science behind these medications is considerably more serious.

They are not magic injections, nor are they simply cosmetic shortcuts. For people who medically qualify, they can be powerful tools in treating obesity, diabetes and related metabolic problems. But they are also medications with risks, limitations and consequences when treatment is stopped.

The most important question, then, is not: “How much weight can I lose?” It is: “Do I actually need this medication, and can I use it safely as part of a long-term approach to my health?”

That answer belongs in a doctor's office not on TikTok. When the social-media trend fades, the underlying reality remains: obesity is a chronic medical condition, and treating it requires more than chasing a number on the scale.