Semaglutide vs tirzepatide for weight loss

Research-informed explainer — last updated 2026-04-11

Both semaglutide and tirzepatide cause substantial weight loss, but the clinical data behind each drug differs in size, scope, and which patients were studied. Semaglutide has the longer track record, including large cardiovascular outcomes trials. Tirzepatide targets two hormones instead of one and has shown higher average weight loss numbers when the two have been compared directly. Which belongs in your treatment plan depends on your weight, your blood sugar, your heart health, and whether you have type 2 diabetes.

This explainer is grounded in peer-reviewed research from three specialists listed in the Convene directory: an endocrinologist who was among the lead investigators on several semaglutide cardiovascular trials, a diabetes center director who co-authored the major ADA/EASD consensus statements on type 2 diabetes treatment, and an obesity medicine specialist who co-authored both the AHA/ACC obesity management guidelines and the Endocrine Society's pharmacotherapy guidelines.

What's the difference?

Semaglutide (sold as Ozempic for diabetes and Wegovy for weight management) mimics a hormone called GLP-1 (glucagon-like peptide-1). GLP-1 slows down how fast your stomach empties, signals your brain that you're full, and prompts your pancreas to release insulin when blood sugar rises. The injectable form is given once a week; there's also a daily pill form (Rybelsus) approved for type 2 diabetes.

Tirzepatide (sold as Mounjaro for diabetes and Zepbound for weight management) does everything semaglutide does, and more. It mimics both GLP-1 and a second hormone called GIP (glucose-dependent insulinotropic polypeptide). GIP works on fat tissue and the brain in ways that appear to amplify the weight-loss signal beyond what GLP-1 alone produces. It's also a once-weekly injection.

That second hormone is why tirzepatide tends to produce more weight loss on average. In head-to-head clinical trials, patients on tirzepatide at the highest dose lost more weight than patients on semaglutide 1.0 mg. Individual responses vary — some people do better on semaglutide, and not everyone can tolerate tirzepatide's highest dose.

At a glance

What the semaglutide trials actually showed

The weight loss trial most often cited for semaglutide is STEP 1, published in the New England Journal of Medicine in 2021. It enrolled 1,961 adults who had obesity or overweight with a weight-related condition but did not have type 2 diabetes. Half took semaglutide 2.4 mg weekly, half took a placebo, and everyone received lifestyle counseling. After 68 weeks, the semaglutide group lost an average of 14.9% of their body weight compared to 2.4% in the placebo group [1]. About half of patients in the semaglutide group lost 15% or more of their starting weight, and roughly 86% lost at least 5%.

To put that in concrete terms: for someone weighing 250 pounds, losing 15% means losing 37 pounds. The Endocrine Society's clinical practice guideline on pharmacological obesity treatment, co-authored by Caroline Apovian at Brigham and Women's Hospital and Harvard Medical School, notes that 5% weight loss is the point where metabolic risk factors like blood pressure and cholesterol typically start improving, and that 10% or more is where conditions like sleep apnea and joint pain tend to respond [9].

The cardiovascular evidence for semaglutide goes beyond any other drug in this class. The SELECT trial, published in the New England Journal of Medicine in 2023, enrolled 17,604 people with established cardiovascular disease and obesity who did not have diabetes. Over nearly 40 months of follow-up, patients on semaglutide 2.4 mg had a 20% lower rate of major cardiovascular events — heart attack, stroke, or cardiovascular death — than those on placebo (hazard ratio 0.80, 95% CI 0.72–0.90) [2]. No weight-loss medication had shown that kind of heart protection in people without diabetes before.

The earlier SUSTAIN-6 trial, which enrolled 3,297 people with type 2 diabetes at high cardiovascular risk, found a similar reduction in MACE with injectable semaglutide compared to placebo (HR 0.74) over two years [3]. A separate trial of oral semaglutide (PIONEER-6) confirmed cardiovascular noninferiority in a similar high-risk diabetic population [4].

What the tirzepatide trials showed

Tirzepatide's weight loss trials (the SURPASS and SURMOUNT programs) show larger average weight loss numbers. The SURMOUNT-1 trial, the equivalent of STEP 1 for tirzepatide, found average weight loss of about 20–22% of body weight at the highest dose (15 mg) after 72 weeks in adults with obesity without diabetes. That's roughly 5–7 percentage points more than semaglutide in a comparable non-diabetic population.

What tirzepatide doesn't have yet is a completed cardiovascular outcomes trial in people without diabetes. The SURPASS-CVOT trial is ongoing. The ADA/EASD consensus framework, developed in part by John Buse at the University of North Carolina and updated in 2018, recommends GLP-1 receptor agonists and related agents for patients at high cardiovascular risk — a recommendation made partly on the strength of semaglutide's outcomes data [5]. Whether tirzepatide will show the same or greater cardiovascular benefit is an open question that the outcomes trial is designed to answer.

When semaglutide is typically recommended

Semaglutide is the more established choice when cardiovascular risk is a primary concern. For anyone with existing heart disease, a prior heart attack, or high cardiovascular risk alongside obesity, SELECT's results are directly relevant. The drug is also available in an oral form for people who strongly prefer not to inject.

Semaglutide has been on the market longer, which means more real-world experience with long-term tolerability, drug interactions, and how patients actually do outside clinical trials. It also has more completed outcomes data than any other drug in this category.

When tirzepatide is typically recommended

Tirzepatide tends to come up first when the goal is maximum weight loss and the patient doesn't have established cardiovascular disease that would make SELECT's data directly relevant. It's become a common choice for people with severe obesity or those who need to lose a substantial amount of weight before surgery.

For patients with type 2 diabetes, tirzepatide produces larger HbA1c reductions than semaglutide at comparable doses, alongside the greater weight loss. The ADA/EASD treatment framework, which John Buse helped shape over multiple editions, centers drug selection on individual patient goals — glycemic control, weight loss, cardiovascular risk, kidney protection — rather than a fixed hierarchy [5][6][7]. For a patient whose main challenge is blood sugar control and excess weight, tirzepatide's dual mechanism may offer more benefit in both domains.

Side effects: mostly similar

Both drugs cause similar side effects, primarily gastrointestinal: nausea, diarrhea, vomiting, and constipation. These are most common when starting the drug or increasing the dose, and they usually settle down after a few weeks. Both medications are started at a low dose and titrated up slowly over months specifically to reduce this problem.

Neither drug is appropriate if you have a personal or family history of a rare thyroid cancer called medullary thyroid carcinoma, or if you have a condition called multiple endocrine neoplasia syndrome type 2. Both carry warnings about pancreatitis and gallbladder disease. Your doctor will review your full medical history before prescribing.

One practical difference: at the highest doses, tirzepatide's gastrointestinal side effects tend to be more frequent than semaglutide's, because the higher weight loss ceiling comes with a stronger hormonal effect on the gut.

Insurance and cost

Both drugs are expensive without coverage, often over $1,000 per month at list price. Coverage varies by plan. Wegovy (semaglutide for weight loss) and Zepbound (tirzepatide for weight loss) have different coverage profiles — some plans cover one but not the other, and some cover neither. Your doctor's office or a specialty pharmacy can check your coverage and walk you through manufacturer savings programs, which both Novo Nordisk and Eli Lilly offer for eligible patients.

Questions to ask your doctor

• Do I have risk factors that make the cardiovascular outcomes data for semaglutide particularly relevant to my situation?
• What weight loss target would make a meaningful difference for my health, and which drug is more likely to get me there?
• If I try one and tolerate it well but don't see enough weight loss, is it reasonable to switch to the other?
• How long would I typically stay on this medication — is this a short-term bridge or a long-term treatment?
• What happens to weight when the medication is stopped, and how does that affect the decision?
• What does dose titration look like, and what's the plan if side effects make it hard to reach the target dose?

The bottom line

Semaglutide has more cardiovascular outcomes data behind it than any other weight loss drug. SELECT showed it reduces heart attacks and strokes in people with obesity and existing cardiovascular disease. No other weight loss medication has done that in a completed randomized trial. Tirzepatide produces more weight loss on average, because the GIP component appears to add to what GLP-1 alone does.

If you don't have heart disease and your main goal is weight loss, tirzepatide's larger average effect size is a reasonable place to start the conversation with your doctor. If you do have heart disease or high cardiovascular risk, semaglutide's documented heart protection matters — especially while tirzepatide's outcomes trial is still running. The specifics of your health history are what should drive the decision, and an endocrinologist or obesity medicine specialist can help you work through them.