Ozempic vs Wegovy vs Zepbound: Which GLP-1 Is Right for You?

What Is the Difference Between Ozempic and Wegovy?

Ozempic and Wegovy are the same molecule, semaglutide, at different doses and with different FDA approvals. Ozempic (0.5 mg, 1 mg, 2 mg weekly) is approved only for glycemic control in type 2 diabetes and cardiovascular risk reduction. Wegovy (2.4 mg weekly) is approved for chronic weight management in adults with a BMI of 30 or higher, or a BMI of 27 or higher with at least one weight-related comorbidity such as hypertension, sleep apnea, or dyslipidemia.

The practical difference shows up at the pharmacy counter, not in the vial. Because Ozempic carries no obesity indication, prescribing it for weight loss is off-label, and most insurance plans will not cover it for that purpose. Wegovy's 2.4 mg dose also appears to drive more weight loss than the 1 to 2 mg doses used in diabetes trials. In STEP-1 (N=1,961), participants without diabetes who received semaglutide 2.4 mg lost a mean of 14.9% of body weight over 68 weeks compared with 2.4% for placebo (P<0.001) [1]. The same trial reported that 86.4% of participants on semaglutide achieved at least 5% weight loss versus 31.5% on placebo.

Both drugs share an identical 20-week titration schedule: 0.25 mg for weeks 1, 4 to 0.5 mg for weeks 5, 8 to 1 mg for weeks 9, 12 to 1.7 mg for weeks 13, 16, and the 2.4 mg maintenance dose from week 17 onward per the Wegovy FDA label [2].

Wegovy vs Zepbound: How Do They Compare on Weight Loss?

Zepbound consistently produces more weight loss than Wegovy in separate Phase 3 trials, though no direct randomized head-to-head trial has been published as of early 2025. In SURMOUNT-1 (N=2,539), adults with obesity or overweight treated with tirzepatide 15 mg lost a mean of 20.9% of body weight at 72 weeks versus 3.1% for placebo (P<0.001) [3]. The 10 mg dose group lost 19.5%, and the 5 mg dose group lost 15.0%. Those numbers all exceed Wegovy's STEP-1 result of 14.9%, although the trial populations differed slightly.

The mechanism explains part of this gap. Semaglutide acts only on GLP-1 receptors. Tirzepatide is a dual GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptor agonist. GIP receptor activation appears to amplify weight reduction through complementary pathways involving adipose tissue and central appetite regulation. The Zepbound FDA label notes that tirzepatide's GIP activity contributes to both insulin secretion and glucagon suppression in a glucose-dependent manner [4].

STEP-5 followed patients on Wegovy for 104 weeks and found sustained mean weight loss of 15.2%, with continued glycemic and cardiometabolic improvements [5]. Tirzepatide's maintenance data from SURMOUNT-4 (N=670) showed that patients who continued on tirzepatide maintained a 5.5% additional weight reduction over weeks 36, 88, while those switched to placebo regained 14.8 percentage points of their lost weight within one year (P<0.001) [6]. Both drugs require long-term, likely indefinite, use to preserve results.

Mounjaro vs Zepbound: Same Drug, Different Labels

Mounjaro and Zepbound contain identical active ingredients. Both are tirzepatide at the same doses (2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg weekly). Mounjaro is FDA-approved for type 2 diabetes glycemic control. Zepbound is FDA-approved for chronic weight management. Prescribing Mounjaro for weight loss without a diabetes diagnosis is off-label, mirroring the Ozempic/Wegovy distinction exactly.

The insurance implications are material. A patient with type 2 diabetes and obesity could reasonably be prescribed Mounjaro for glucose control and benefit from weight reduction as a secondary effect. A patient with obesity but no diabetes needs a Zepbound prescription to have any realistic chance of insurance coverage. SURMOUNT-2 (N=938) evaluated tirzepatide specifically in patients with type 2 diabetes and found mean weight reductions of 13.9% and 15.7% for the 10 mg and 15 mg doses respectively at 72 weeks [7], confirming meaningful weight loss even in the diabetes population where semaglutide's STEP-2 data showed 9.6% at the 2.4 mg dose [8].

Semaglutide vs Tirzepatide: The Clinical Decision Framework

Choosing between semaglutide and tirzepatide depends on five variables that a clinician should evaluate at the initial consultation.

1. Degree of weight loss needed. If a patient requires more than 15% weight reduction to meaningfully reduce a comorbidity burden (for example, severe sleep apnea, weight-bearing joint disease, or pre-surgical optimization), tirzepatide's higher ceiling makes it the stronger first choice based on current Phase 3 data.

2. Type 2 diabetes status. Semaglutide has strong A1C data across STEP-2 [8] and SELECT, with a 1.6% mean A1C reduction at the 2.4 mg dose in patients with diabetes. Tirzepatide showed a mean A1C reduction of 2.1% at 15 mg in SURMOUNT-2 [7]. Both are effective, but tirzepatide's dual receptor action may provide a slight glycemic edge in patients with higher baseline A1C values.

3. Cardiovascular history. Only semaglutide currently has a dedicated cardiovascular outcomes trial in the obesity population. SELECT (N=17,604) enrolled adults with overweight or obesity, established cardiovascular disease, but without diabetes, and found that semaglutide 2.4 mg reduced major adverse cardiovascular events (MACE) by 20% over a mean follow-up of 39.8 months (HR 0.80 to 95% CI 0.72, 0.90, P<0.001) [9]. Tirzepatide's cardiovascular outcomes trial (SURPASS-CVOT) was ongoing at time of writing, so clinicians managing high-risk cardiac patients may lean toward semaglutide pending those results.

4. Tolerability and prior GLP-1 exposure. A patient who previously tried a lower-dose GLP-1 such as liraglutide (Saxenda) and found nausea intolerable may not tolerate semaglutide or tirzepatide either. STEP-8 (N=338) showed semaglutide 2.4 mg produced 15.8% weight loss versus 6.4% for liraglutide 3 mg at 68 weeks (P<0.001) [10], so switching up rather than stopping is often worth attempting under closer monitoring. Tirzepatide's nausea profile at 15 mg is broadly similar to semaglutide 2.4 mg in trial populations.

5. Cost and access. Wegovy's 2024 U.S. list price is approximately $1,349 per month; Zepbound's list price is approximately $1,060 per month. Neither is universally covered. The American Association of Clinical Endocrinology (AACE) obesity guidelines state that pharmacotherapy should be added to lifestyle intervention "when BMI is 30 or higher, or 27 or higher with weight-related comorbidities, and lifestyle modification alone has not produced adequate results" [11]. Access barriers, particularly insurance exclusions for anti-obesity medications, remain the most common reason patients cannot start or continue either drug class.

GLP-1 vs Phentermine: An Older Drug Still in the Picture

Phentermine is a sympathomimetic amine approved since 1959. Short. Cheap. Still widely prescribed. Its mean weight loss in 12-week randomized trials ranges from 3.6% to 6.0% of body weight, substantially below GLP-1 outcomes. It carries FDA approval only for short-term use (typically up to 12 weeks) because of cardiovascular concerns including elevated heart rate and blood pressure.

Phentermine-topiramate ER (Qsymia) extends that window and produces 8.8 to 10.9% weight loss at 56 weeks in EQUIP/CONQUER trial data, narrowing the gap with semaglutide but still falling short of tirzepatide's 20.9% ceiling. GLP-1 agents also reduce cardiovascular events (SELECT) and improve glycemic outcomes, benefits that phentermine does not share.

Phentermine remains a reasonable option when a patient has contraindications to GLP-1 agents (personal or family history of medullary thyroid carcinoma or MEN2 syndrome, severe GI dysmotility), when cost is prohibitive, or when a short-term bridge is needed before starting an injectable. At less than $30 per month generically, phentermine's cost advantage is real. The clinical tradeoff is a roughly 10-to-15 percentage-point difference in expected weight loss.

STEP-3 (N=611) showed that semaglutide 2.4 mg combined with intensive behavioral therapy (IBT) produced 16.0% weight loss at 68 weeks versus 5.7% for IBT plus placebo [12]. No comparable IBT-augmentation trial exists for phentermine at those durations, underscoring how different the evidence bases are.

Side Effects, Contraindications, and Safety Signals

Both semaglutide and tirzepatide share a side-effect profile dominated by gastrointestinal events. In STEP-1, nausea occurred in 44% of semaglutide-treated patients versus 16% on placebo, vomiting in 24% versus 6%, and diarrhea in 30% versus 16% [1]. SURMOUNT-1 showed similar rates for tirzepatide: nausea 32 to 42% depending on dose, vomiting 17 to 25%, and diarrhea 17 to 30% [3]. These events are mostly mild-to-moderate and peak during the first 4 to 8 weeks of each dose increase.

Rare but serious concerns for both drug classes include:

• Pancreatitis. Both drugs carry a label warning. The absolute incidence in trials was low (fewer than 1% in STEP-1 and SURMOUNT-1), but patients with a history of pancreatitis should use either drug cautiously or not at all.
• Medullary thyroid carcinoma (MTC). Rodent studies showed dose-dependent thyroid C-cell tumors with both drugs. Neither the Wegovy nor the Zepbound label has demonstrated MTC in humans at clinical doses, but both carry black-box warnings, and both are contraindicated in patients with a personal or family history of MTC or MEN2.
• Gallbladder disease. Rapid weight loss of any cause increases cholelithiasis risk. Cholecystitis was reported in 2.5% of Wegovy patients versus 1.2% on placebo in pooled STEP data.
• Gastroparesis-like symptoms. The FDA added a label update in 2023 noting reports of gastroparesis with GLP-1 receptor agonists. Patients with pre-existing gastric dysmotility warrant careful evaluation before prescribing.

AACE/ACE guidelines recommend baseline evaluation of thyroid history, personal or family MTC risk, and pancreatic enzyme levels before initiating therapy in high-risk individuals [11].

Titration Schedules and Practical Dosing

Both drugs use a slow titration to reduce GI side effects.

Wegovy (semaglutide): Start 0.25 mg weekly for 4 weeks, then 0.5 mg, 1 mg, 1.7 mg, and finally 2.4 mg at week 17. If a patient cannot tolerate a dose increase, the Wegovy label permits a 4-week delay before the next escalation.

Zepbound (tirzepatide): Start 2.5 mg weekly for 4 weeks, then increase by 2.5 mg every 4 weeks to a target of 5 mg, 10 mg, or 15 mg based on response and tolerability. The full 15 mg dose is reached at approximately week 20.

Missing a dose by more than 5 days (for semaglutide) or 4 days (for tirzepatide) means skipping that dose and resuming on the next scheduled day. Patients who discontinue for more than 4 weeks should generally restart at the lowest dose and re-titrate. Both drugs are injected subcutaneously in the abdomen, thigh, or upper arm, and injection sites should be rotated weekly.

Who Should NOT Start a GLP-1 Agent?

Absolute contraindications apply to both drug classes. Patients with a personal or family history of MTC or MEN2 syndrome must not use semaglutide or tirzepatide. Pregnancy is another absolute contraindication. Both drugs should be stopped at least 2 months before a planned conception attempt per the Wegovy label [2].

Relative contraindications that require individualized risk-benefit assessment include a history of acute pancreatitis, severe gastroparesis, inflammatory bowel disease with active flares, and diabetic retinopathy in patients with rapidly fluctuating glucose levels (rapid glycemic improvement has been associated with transient worsening of retinopathy in high-risk eyes). Patients on insulin or sulfonylureas need dose reductions in those agents when starting a GLP-1 to prevent hypoglycemia.

Patients with an eGFR below 15 mL/min/1.73m² (end-stage kidney disease) have limited data and should discuss risk with a nephrologist before starting either agent.

The Maintenance Problem: What Happens When You Stop?

Stopping either drug leads to weight regain. SURMOUNT-4 showed that patients who switched from tirzepatide to placebo after 36 weeks of treatment regained a mean 14.8 percentage points of weight over the next 52 weeks, retaining only about half of their initial loss [6]. STEP-1's extension data showed similar patterns for semaglutide, with roughly two-thirds of lost weight returning within one year of discontinuation.

This pattern mirrors the physiology of obesity as a chronic condition. The Endocrine Society's position statement describes obesity as a "chronic, relapsing, multifactorial disease" in which weight-regulatory hormones do not return to pre-obesity baselines after weight loss alone. Patients should be counseled before starting therapy that these drugs are likely long-term commitments, not finite courses. Stopping because "the weight is gone" without a clear maintenance plan reliably results in regain.

SURMOUNT-3 (N=579) studied tirzepatide in patients who first completed a 12-week intensive lifestyle intervention producing 6.9% weight loss, then were randomized to tirzepatide 15 mg or placebo. The tirzepatide group achieved an additional 18.4% reduction from randomization baseline, for a total of 24.3% weight loss from the original starting weight [13]. The lesson: lifestyle intervention and pharmacotherapy stack.

Insurance, Compounding, and Access in 2025

As of early 2025, Medicare Part D covers Wegovy for cardiovascular risk reduction in patients who meet SELECT-like criteria (established CVD, BMI of 27 or higher), following the SELECT trial results and a subsequent CMS coverage determination. Medicare does not yet broadly cover GLP-1 agents for obesity without CVD, though legislation to expand coverage was pending in Congress.

Compounded semaglutide and tirzepatide became widespread during the FDA drug shortage period of 2022 to 2024. The FDA removed both semaglutide and tirzepatide from the drug shortage list in 2024, which means 503A and 503B compounders are no longer permitted to produce copies of these specific molecules. Patients using compounded versions should discuss transitioning to branded products with their prescriber, as compounded formulations do not carry FDA approval for safety, efficacy, or sterility and the quality can vary significantly between compounding pharmacies.

The AACE/ACE 2016 obesity guidelines, still the most widely cited framework for U.S. obesity pharmacotherapy, explicitly state that medication selection should be "individualized based on efficacy, safety profile, cost, and patient comorbidities" [11]. That four-part rubric is still the right place to start the conversation.