How Ozempic, Wegovy, and Mounjaro Really Work: A Registered Dietitian Explains the Science Behind Weight Loss Medications
In this video I explain how these weight loss/obesity/Type 2 Diabetes medications like Ozempic, Wegovy, Rybelsus, Mounjaro, and Zepbound work.
If you've heard names like Ozempic, Wegovy, or Mounjaro in the news or seen them advertised for weight loss, you're not alone. But how do these medications actually work? And what should you know before starting them?
Hi, I’m Kara McIver, a registered dietitian helping young and middle-aged adults reduce their risk of chronic diseases like type 2 diabetes, heart disease, and Alzheimer’s. If you’re exploring weight loss medications or trying to better understand how they support health—not just weight—this post is for you.
What Is Semaglutide?
Semaglutide is the active ingredient in medications like Ozempic, Wegovy, and Rybelsus. It mimics a hormone in your body called GLP-1 (glucagon-like peptide-1). This hormone plays a major role in regulating blood sugar and appetite.
Because of its structure, semaglutide is part of a drug class called GLP-1 receptor agonists, often referred to simply as GLP-1s. Originally developed for type 2 diabetes, semaglutide has proven effective in reducing body weight as a secondary benefit—which is why it’s now widely prescribed for obesity management too.
How Semaglutide Works in the Body
Semaglutide helps your body lower blood sugar and manage appetite in three key ways:
1. Increases Insulin Production
When you eat, semaglutide boosts the release of insulin—your body’s “key” that unlocks cells so sugar can enter. More insulin helps reduce blood sugar levels and keeps energy flowing into your muscles and organs, not stuck in your bloodstream.
2. Reduces Sugar Release from the Liver
In people with type 2 diabetes, the liver often dumps sugar into the blood even when it’s not needed. Semaglutide helps stop this unnecessary sugar release, keeping your blood glucose levels more stable.
3. Slows Down Digestion
Semaglutide delays how quickly food leaves your stomach. This helps in two important ways:
You feel fuller longer, reducing cravings and snacking.
Sugar enters your bloodstream more slowly, giving your insulin time to “keep up.”
Think of it like slowing down a candy conveyor belt so your body can handle the sugar at a manageable pace.
Why These Medications Cause Weight Loss
Weight loss wasn’t the original goal of semaglutide—but it quickly became one of its biggest benefits.
Here’s why:
Less hunger and more satiety = fewer calories consumed.
Less sugar flooding the blood = less fat stored.
Better insulin response = more energy going to cells, not fat tissue.
As a registered dietitian, I always emphasize that weight loss alone doesn’t define health. But in this case, the mechanisms that lead to weight loss are also improving blood sugar, metabolism, and appetite regulation—critical aspects of disease prevention.
Ozempic vs. Wegovy vs. Rybelsus: What’s the Difference?
All three are semaglutide-based, but they’re approved for different uses.
💡 Important: Even though they contain the same active drug, insurance coverage often varies, and off-label use (like using Ozempic for weight loss without diabetes) may not be covered.
Mounjaro (Tirzepatide): A Step Beyond Semaglutide?
Enter tirzepatide, the active ingredient in Mounjaro and Zepbound. These medications combine GLP-1 action with GIP (gastric inhibitory polypeptide) to further slow digestion and enhance appetite suppression.
Clinical research shows tirzepatide leads to even more weight loss than semaglutide—making it an important option for patients who need more intensive intervention or haven’t responded to GLP-1s alone.
Both are weekly injections and not available as oral pills.
Should You Get These Medications Online?
While some online and compounding pharmacies advertise low-cost weight loss medications, be cautious. These versions are not FDA-approved, and changes in formulation could mean:
Reduced effectiveness
Unknown side effects
Higher health risks
🚨 If you’re experiencing symptoms like blurred vision, stomach pain, or mood changes, an online prescriber or esthetician's office likely won’t have the training to help. Please work with a licensed medical provider and ideally, a registered dietitian to safely manage medication, nutrition, and side effects.
So, What’s Next?
Weight loss medications like Ozempic and Mounjaro are powerful tools—but they’re not magic bullets. For lasting health, they should be paired with:
A nutrient-dense, balanced diet
Physical activity
Support from a qualified healthcare team
In my next blog post, I’ll cover foods to eat while on Ozempic and how to build a semaglutide diet that prevents nutrient deficiencies and supports long-term health.
Final Thoughts from a Registered Dietitian
Weight loss medications aren’t for everyone—but for people with obesity or uncontrolled blood sugar, they can be life-changing. The science behind semaglutide and tirzepatide is strong, and when used responsibly, these medications can do more than shrink your waistline—they can help you live longer and healthier.
If you're considering these options, talk to your doctor and connect with a registered dietitian who can help you navigate the food, nutrition, and lifestyle choices that matter most while you're on these medications.