Weight Loss Drugs: Ozempic, Wegovy & Mounjaro Explained

What Are These Drugs and How Do They Work?

All three belong to a class of medications that mimic hormones naturally produced in the gut after eating.

Ozempic and Wegovy both contain semaglutide, a GLP-1 receptor agonist (glucagon-like peptide-1). GLP-1 is a hormone released after meals that signals fullness to the brain, slows gastric emptying, and stimulates insulin release. Ozempic is approved for type 2 diabetes management; Wegovy contains a higher dose of the same molecule and is approved specifically for chronic weight management. Both are manufactured by Novo Nordisk.

Mounjaro (tirzepatide, manufactured by Eli Lilly) is a dual agonist — it activates both GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors. GIP is a second gut hormone involved in fat storage and energy regulation. This dual mechanism appears to produce greater weight loss than GLP-1 agonists alone. In the United States, tirzepatide is also approved under the brand name Zepbound specifically for weight management.

In plain terms: these drugs make the brain receive stronger and longer "I'm full" signals, reduce appetite significantly, and slow down how quickly the stomach empties — so people eat less without the constant struggle of willpower.

What the Clinical Evidence Shows

The trial data on these medications is, by obesity treatment standards, remarkable.

The STEP 1 trial, published in the New England Journal of Medicine in 2021, found that participants taking semaglutide 2.4 mg (Wegovy) lost an average of 14.9% of their body weight over 68 weeks, compared to 2.4% in the placebo group. The SURMOUNT-1 trial for tirzepatide, also published in the New England Journal of Medicine in 2022, showed average weight loss of up to 22.5% of body weight at the highest dose — approaching the results seen with sleeve gastrectomy.

Crucially, both trials also showed improvements in cardiovascular risk factors: blood pressure, cholesterol, blood sugar, and waist circumference all improved alongside weight loss.

The SELECT trial (2023), published in the New England Journal of Medicine, added a further significant finding: semaglutide reduced the risk of major cardiovascular events — heart attack, stroke, or cardiovascular death — by 20% in overweight or obese adults who already had cardiovascular disease, regardless of diabetes status.

Who Are These Medications For?

These are not lifestyle supplements or cosmetic treatments. They are prescription medications with specific approved indications.

In most regulatory frameworks, GLP-1 and dual agonist medications for weight management are indicated for adults with a BMI of 30 or above (obesity), or a BMI of 27 or above (overweight) with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or high cholesterol.

They are not approved for people who are mildly overweight without comorbidities. They are not appropriate for people with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2 (MEN 2) — a contraindication identified in animal studies and carried as a boxed warning by the FDA.

They also require ongoing commitment. Weight regained rapidly when the medication is stopped — a finding confirmed in the STEP 1 extension study — which means these drugs function more like a long-term management tool than a finite course of treatment.

[REVIEWER: add clinical insight here — e.g., how you assess patient suitability in practice, what questions you ask before prescribing or referring, and what patients most commonly misunderstand about these medications]

Side Effects: What Patients Should Know

The most common side effects are gastrointestinal — nausea, vomiting, diarrhoea, and constipation. These are particularly prevalent during dose escalation, which is why all three medications are started at a low dose and increased gradually over several months.

For most patients, GI side effects are manageable and reduce over time. For some, they are severe enough to discontinue treatment.

More serious concerns flagged in prescribing information and ongoing pharmacovigilance include:

• Pancreatitis — inflammation of the pancreas. Patients should be aware of the symptoms: sudden, severe abdominal pain radiating to the back.

• Gallbladder disease — cholelithiasis (gallstones) and cholecystitis occurred at higher rates in clinical trials than in placebo groups.

• Thyroid tumours — a boxed warning based on animal studies. While causation in humans has not been established, people with relevant personal or family history should not use these drugs.

• Muscle loss — emerging research suggests that a significant portion of weight lost on GLP-1 agonists may be lean muscle mass rather than fat alone. Adequate protein intake and resistance exercise are increasingly recommended alongside treatment, though evidence-based protocols are still being established.

• "Ozempic face" — a colloquial term for the gaunt facial appearance that can result from rapid fat loss. Cosmetically notable, clinically not a primary concern.

The FDA and European Medicines Agency (EMA) continue to monitor reports of psychiatric side effects — including suicidal ideation — though a causal link has not been confirmed, and both agencies have so far not found sufficient evidence to alter prescribing guidance.

[REVIEWER: add clinical insight here — e.g., how you manage nausea during dose escalation, or what you tell patients who are concerned about muscle loss or long-term use]

The Access and Cost Problem

In much of the world, including India, these medications are not widely accessible. Wegovy is not yet approved by the Central Drugs Standard Control Organisation (CDSCO) in India as of 2024. Ozempic is available but primarily through endocrinologists for diabetes management. Mounjaro has more recently entered select markets.

Where available, costs are significant. In the United States, Wegovy lists at over $1,300 per month without insurance coverage — a figure that has sparked considerable political debate. Compounded versions of semaglutide proliferated during shortage periods, raising serious safety concerns; the FDA issued repeated warnings about the risks of unregulated compounded injectables.

For patients in India seeking these treatments, a consultation with a qualified endocrinologist or physician with experience in obesity medicine is the correct starting point — not social media or online pharmacies.

What These Drugs Are Not

They are not a substitute for lifestyle change — physical activity and dietary habits remain important for long-term health regardless of medication. They are not appropriate for short-term cosmetic weight loss in people without clinical obesity or related conditions. And they are not a permanent fix: without continued use, most patients regain substantial weight within one to two years of stopping, according to the STEP 1 extension data.

The broader cultural conversation around these drugs — driven partly by celebrity use and social media — has created demand that significantly outpaces appropriate clinical use. That gap is where harm happens.

FAQ

Q: What is the difference between Ozempic and Wegovy? Both contain semaglutide, the same active molecule. Ozempic is approved for type 2 diabetes at doses up to 2 mg weekly. Wegovy is approved for chronic weight management at a higher dose of 2.4 mg weekly. Using Ozempic off-label for weight loss — as widely reported — is not the same as using the dose and formulation studied for that purpose.

Q: How much weight can you lose on Mounjaro? In the SURMOUNT-1 trial published in the New England Journal of Medicine, participants on the highest dose of tirzepatide (Mounjaro) lost an average of 22.5% of their body weight over 72 weeks. Results vary by individual. These figures come from controlled trial conditions with dietary and lifestyle support alongside medication.

Q: Are these weight loss injections safe long-term? Long-term safety data is still accumulating, as these drugs have only been widely used for a few years. Existing trial data up to 72–104 weeks shows a manageable side-effect profile for most patients. Ongoing post-market surveillance by the FDA and EMA continues to monitor rare but serious risks including thyroid tumours, pancreatitis, and — more recently — potential psychiatric effects.

Q: Can you take Ozempic or Wegovy if you don't have diabetes? Wegovy is approved for weight management in people without diabetes who meet the BMI criteria (30+, or 27+ with a weight-related health condition). Ozempic is approved for type 2 diabetes only — its widespread off-label use for weight loss in people without diabetes is medically and legally distinct from its approved indication.

Q: What happens when you stop taking these medications? Most patients regain significant weight after stopping. The STEP 1 extension trial found that participants who discontinued semaglutide regained approximately two-thirds of their lost weight within one year. This reflects the chronic nature of obesity as a condition — not a personal failure — and underscores why these medications are positioned as long-term treatments rather than short courses.