Four brand names dominate almost every conversation about weight loss medications right now: Ozempic, Wegovy, Mounjaro, and Zepbound. They show up in news coverage, insurance disputes, and group chats, often used as if they were interchangeable. Some of them are. Some of them aren't.
Behind the four brands sit only two active ingredients. Semaglutide is sold as Ozempic and Wegovy. Tirzepatide is sold as Mounjaro and Zepbound. The differences between the brands come down to approved uses, doses, delivery formats, and price, while the differences between the two molecules come down to how they act in the body and how they performed when researchers tested them side by side.
Two Molecules, Four Brand Names
Semaglutide: Ozempic and Wegovy
Ozempic is approved for adults with type 2 diabetes, with doses that step up from 0.25 mg to a maximum of 2 mg once a week. Wegovy uses the same molecule at higher doses and is approved for chronic weight management.
Wegovy's label has grown since 2021. The FDA added an adolescent indication for ages 12 and older in December 2022 and cardiovascular risk reduction for adults with established cardiovascular disease and overweight or obesity in March 2024.
Tirzepatide: Mounjaro and Zepbound
Mounjaro is approved for type 2 diabetes, and Zepbound is approved for chronic weight management in adults. In December 2024, the FDA also approved Zepbound for moderate to severe obstructive sleep apnea in adults with obesity. Both brands use the same dose range, from a 2.5 mg starting dose up to 15 mg weekly. The FDA's 2023 announcement for Zepbound stated plainly that tirzepatide, its active ingredient, "is already approved under the trade name Mounjaro."
Why the Same Drug Gets Different Brand Names
Drugmakers market separate brands when a molecule is approved for different conditions, often at different doses and with different labeling. That split has practical effects. Insurance plans frequently cover diabetes medications and weight management medications under different rules. It's why someone asking a pharmacist about "Ozempic or Mounjaro" for weight loss may hear about Wegovy or Zepbound instead.
The Approval Timeline
Each brand arrived on the U.S. market at a different point, which explains why Ozempic became the household name:
- Ozempic (semaglutide), approved in 2017 for type 2 diabetes
- Wegovy (semaglutide), approved June 4, 2021, for chronic weight management
- Mounjaro (tirzepatide), approved May 13, 2022, for type 2 diabetes
- Zepbound (tirzepatide), approved November 8, 2023, for chronic weight management
Ozempic had a head start of more than three years on the others. Wegovy faced supply shortages after launch, and the diabetes brand ended up as the cultural shorthand for the whole category.
How Semaglutide and Tirzepatide Differ
One Receptor Versus Two
Semaglutide activates the GLP-1 receptor. Tirzepatide activates two receptors: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). According to the FDA, this dual action reduces appetite and food intake.
Lilly's 2022 announcement described Mounjaro as a first-in-class medicine for that reason. Whether the second receptor accounts for the differences seen in trials is still an open research question, but it's the core chemical distinction between Mounjaro versus Ozempic.
Doses, Devices, and Weekly Injections
All four brands are weekly injections for losing weight or managing blood sugar, given under the skin. Wegovy steps up to 2.4 mg, and in March 2026 the FDA approved Wegovy HD, a 7.2 mg dose for adults who have tolerated 2.4 mg for at least four weeks. Zepbound comes in more formats than it did at launch. In February 2026, it added a multi-dose KwikPen that holds four weekly doses, a month's supply in one device.
Semaglutide Versus Tirzepatide: The Head-to-Head Trial
What SURMOUNT-5 Tested
For years, comparisons between the drugs relied on separate trials. SURMOUNT-5 changed that. Published in The New England Journal of Medicine in 2025, the trial randomized 751 adults with obesity at 32 sites in the U.S. and Puerto Rico. Participants took the maximum tolerated dose of either tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg) weekly for 72 weeks. In practical terms, it was a Zepbound vs. Wegovy trial.
Weight and Waist Results
Tirzepatide produced a mean weight reduction of 20.2%, compared with 13.7% for semaglutide. That works out to an average of 22.8 kg versus 15.0 kg.
Waist circumference followed the same pattern: down 18.4 cm with tirzepatide and 13.0 cm with semaglutide. People on tirzepatide were also more likely to reach each weight-loss threshold the researchers tracked, from 10% up to 25%.
Where Wegovy HD Fits
SURMOUNT-5 used Wegovy's 2.4 mg maximum because the higher dose didn't exist yet. Novo Nordisk's STEP UP trial tested the 7.2 mg dose and reported a mean weight loss of 20.7% at 72 weeks, according to the company's announcement.
That number comes from a separate trial with different participants, so it can't be compared directly with SURMOUNT-5's tirzepatide result. No published head-to-head trial has yet pitted Wegovy HD against Zepbound.
The Problem With Compounded Versions
During shortages, compounding pharmacies sold their own versions of semaglutide and tirzepatide. The FDA's guidance on unapproved GLP-1 drugs, updated October 1, 2026, notes that compounded drugs aren't FDA-approved and aren't reviewed for safety, effectiveness, or quality before sale.
As of May 31, 2026, the FDA had received 990 adverse event reports tied to compounded semaglutide and more than 730 tied to compounded tirzepatide. It believes these are underreported. The agency has also logged dosing errors, some requiring hospitalization, linked to compounded injectable semaglutide.
Switching From Ozempic to Mounjaro
Why People Switch
Switching from Ozempic to Mounjaro, or from Wegovy to Zepbound, is a prescribing decision. It depends on why the current medication isn't working for you, what your coverage allows, and your medical history.
- No Direct Dose Conversion: There's no validated dose conversion between semaglutide and tirzepatide. The Pharmaceutical Journal attributes this to the drugs' different receptor profiles, which means a given semaglutide dose doesn't translate to a matching tirzepatide dose. Online conversion charts circulate widely, but they reflect rough comparisons, not an established equivalence. Deviating from standard dose schedules can increase side effects, according to the same article.
- Starting Dose and Timing: Tirzepatide initiation begins at 2.5 mg weekly. The Pharmaceutical Journal describes two timing approaches for switching between these drugs: a washout of one to two weeks, or starting the new drug on the day the next weekly dose would have been due.
The FDA's Zepbound labeling states that it shouldn't be used in combination with Mounjaro or a GLP-1 receptor agonist. The same principle applies across the brands: these drugs aren't meant to be stacked.
What These Drugs Cost Without Insurance
The Cost of Wegovy Without Insurance
List prices and cash prices are two different numbers. Fierce Pharma reported in February 2026 that Novo Nordisk sells Wegovy at $349 a month for self-pay patients across all doses. New self-pay patients could pay $199 for each of their first two months on the starter doses.
Novo also announced it would cut the list price of Ozempic, Wegovy, and Rybelsus to $675 a month starting January 1, 2027. That change mainly affects people whose insurance costs are tied to list price, such as those on high-deductible plans.
Ozempic Self-Pay Pricing
Ozempic's self-pay price is $349 a month for all doses except 2 mg, which costs $499, according to the same reporting. The oral Wegovy pill launched with a $149 monthly self-pay price for its starting doses, rising to $299 for the higher strengths. Prices in this market have changed several times in a year. Check the manufacturer's current pricing before you budget around any figure here.
Zepbound Vials and the KwikPen
Lilly cut Zepbound vial prices in December 2025. The 2.5 mg starting dose costs $299 a month, and the highest doses top out at $449. The lower prices on the 7.5 mg to 15 mg doses apply only when you refill within 45 days of your previous delivery.
The KwikPen launched in February 2026 at the same self-pay prices as the vials, starting at $299 for 2.5 mg. These self-pay prices apply to Zepbound; what you pay for Mounjaro depends on your insurance coverage and pharmacy.
Muscle, Fat, and Bone: What Body Composition Research Shows
Muscle Loss on Ozempic and Wegovy
Most of the muscle data on semaglutide comes from Wegovy-dose research, not Ozempic itself. In a DXA substudy of 140 participants from the STEP 1 trial, presented at ENDO 2021 by John Wilding of the University of Liverpool, semaglutide 2.4 mg reduced total fat mass by 19.3% and lean body mass by 9.7% over 68 weeks.
Because fat fell faster than lean mass, the proportion of lean body mass relative to total body mass rose by 3.0 percentage points. Lean mass on a DXA report covers more than muscle, including organs and water, so a lean mass drop isn't a direct measure of muscle loss.
Body Fat Changes After Wegovy
The same STEP 1 analysis tracked visceral fat, the fat stored around the abdominal organs. It fell by 27.4% from baseline, a steeper drop than total fat mass. That's one reason body weight alone gives an incomplete picture. Two people can lose the same number of pounds with different shifts in where fat is stored and how much lean tissue changes.
Bone Loss on Weight Loss Drugs
Bone is the newer part of the conversation. A study by Liu, Walzer, and Stein in the Journal of Clinical Endocrinology and Metabolism in 2026 compared 255 adults taking semaglutide or tirzepatide with 255 matched non-users, all with DXA scans over a median of 17 months.
Among people without diabetes, annualized total hip bone loss was greater in the GLP-1 group (−1% versus −0.6%). Among people with diabetes, bone loss was similar between groups. The authors suggested that weight loss may drive bone loss in people without diabetes, and called for larger prospective studies to see whether the changes affect fracture rates.
In Medical Daily's coverage of the study, the groups suggested for baseline and follow-up DXA screening included postmenopausal women, adults 65 and older, people with a prior fragility fracture or osteoporosis, and those with low BMI.
Body composition can also change for reasons that have nothing to do with medication, which is why changes during perimenopause are worth understanding alongside any medication effects. The FDA hasn't issued specific DXA monitoring guidance for GLP-1 therapy.
Where Nutrition Enters the Picture
Eating less is how these medications reduce weight, which makes the composition of a smaller diet more consequential. Protein, carbohydrate, and fat intake all shape what a body composition scan shows over time.
If you're working out how to structure meals on a reduced appetite, the basics of how your macronutrient split matters offer a starting point to take to a registered dietitian.
Tracking DEXA Body Composition While on GLP-1 Injections
What a DEXA Scan While Taking Ozempic Reports
DEXA (dual-energy X-ray absorptiometry) was the method used in the STEP 1 substudy and the bone study above. A single whole-body scan separates fat mass, lean mass, and bone mineral, and it also estimates visceral fat.
That combination is what makes DEXA body composition data useful during treatment. It shows fat, lean tissue, and bone in one report, rather than a single weight figure.
Tracking Muscle Mass on Mounjaro Over Time
One scan gives a snapshot. A series of scans shows a trend, and the trend is what tells you whether lean mass is holding steady while fat falls.
BOD offers DEXA scanning in Venice, California, with single scans for a starting baseline and monthly and quarterly scan plans for ongoing check-ins. Whatever provider you use, scanning on the same machine under similar conditions makes results easier to compare.
Reading DEXA Scan Results With Your Prescriber
DEXA scan results are most useful when they reach the person managing your prescription. A clinician can read lean mass, fat mass, and bone density changes in the context of your dose, your diet, and your history.
Bring earlier reports along so the comparison is visible. If something in the trend raises questions, your prescriber can decide whether further testing or a change in plan makes sense.
Ozempic and Wegovy are the same molecule, semaglutide, sold for different purposes. Mounjaro and Zepbound are the same molecule, tirzepatide, split the same way. Between the two molecules, the head-to-head SURMOUNT-5 trial found greater average weight loss with tirzepatide and fewer discontinuations due to gastrointestinal side effects, though individual results vary widely.
Beyond the scale, the research points to three things worth watching: lean mass, visceral fat, and bone density. Each can change on these medications, and none of them shows up on a bathroom scale. Cost, switching rules, and new formats like pills and multi-dose pens add practical layers that keep shifting month to month. If you're on one of these medications or considering one, two steps keep the decision grounded. Talk through brand, dose, and cost with your prescriber, and consider a baseline body composition scan so future conversations rest on measured data rather than guesswork.
Sources
- Aronne LJ, Horn DB, le Roux CW, et al. "Tirzepatide as Compared with Semaglutide for the Treatment of Obesity." The New England Journal of Medicine, 2025;393(1):26-36.
- American College of Cardiology. "SURMOUNT-5: Greater Loss of Weight, Waist Circumference With Tirzepatide Than Semaglutide." July 10, 2025.
- Liu Y, Walzer D, Stein EM. "Skeletal effect of semaglutide and tirzepatide in patients with increased risk of fractures." The Journal of Clinical Endocrinology & Metabolism, 2026.
- Endocrine Society. "Semaglutide reduces excess body fat in people with obesity" (Wilding J, STEP 1 body composition analysis, ENDO 2021). March 20, 2021.
- Wilding J, et al. "Impact of Semaglutide on Body Composition in Adults With Overweight or Obesity: Exploratory Analysis of the STEP 1 Study" (abstract).
- U.S. Food and Drug Administration. "FDA Approves New Medication for Chronic Weight Management." November 8, 2023.
- U.S. Food and Drug Administration. "FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss." Updated October 1, 2026.
- Eli Lilly and Company. "FDA Approves Novel, Dual-Targeted Treatment for Type 2 Diabetes." May 13, 2022.
- Eli Lilly and Company. "FDA approves Lilly's Foundayo (orforglipron)." April 1, 2026.
- Novo Nordisk. "Wegovy (semaglutide 2.4 mg), the first and only once-weekly GLP-1 therapy for weight management, approved in the US." June 4, 2021.
- HCPLive. "FDA Approves Higher Dose Semaglutide (Wegovy HD) Injection 7.2 mg for Obesity." March 2026.
- Drugs.com. "Wegovy (semaglutide) FDA Approval History."
- Novo Nordisk. "Wegovy HD (semaglutide 7.2 mg) approved in the US, providing 20.7% mean weight loss." March 2026.
- NPR. "FDA approves weight loss drug Zepbound to treat obstructive sleep apnea." December 21, 2024.
- Fierce Pharma. "Novo to knock down Ozempic, Wegovy list prices next year, but self-pay channels unaffected." February 24, 2026.
- Fierce Pharma. "Lilly joins Novo in GLP-1 self-pay price cuts, lowering costs of single-dose Zepbound vials." December 2025.
- Fierce Pharma. "Lilly adds multidose Zepbound pens to self-pay menu after FDA nod." February 23, 2026.
- ABC News. "Eli Lilly launches new weight-loss drug Zepbound KwikPen: What to know." February 23, 2026.
- Malay Mail (Reuters). "From weight-loss injections to pills: Wegovy goes oral for US users starting at US$149." January 5, 2026.
- Shahid S. "Switching between weight-loss medications." The Pharmaceutical Journal, July 2026.
- Medical Daily. "GLP-1 Weight-Loss Drugs May Be Thinning Bone: Doctors Are Starting to Have This Conversation with Patients." 2026.