Mounjaro vs Ozempic — which one in 2026?

Mounjaro or Ozempic? Both dominate every conversation about weight loss medication right now. And for good reason: both are effective in a way that older treatments simply weren't. But they are not the same drug. In 2026 the evidence has shifted enough that there are clear, data-backed ways to think through the choice.

The first thing worth understanding is that these are different drugs with different mechanisms. Mounjaro (tirzepatide), also sold as Zepbound for weight loss, is a dual agonist: it activates two receptors, GIP and GLP-1. A receptor is the docking point a drug attaches to. Ozempic (semaglutide), also sold as Wegovy for weight loss, activates only the GLP-1 receptor. That extra receptor isn't a minor detail. Researchers believe the dual mechanism is why tirzepatide consistently produces greater weight loss. It may also explain why tirzepatide tends to have a somewhat friendlier stomach side effect profile, despite being the stronger drug.

For years, comparing these two drugs meant stacking data from separate trials run in different populations under different conditions. That always left an asterisk on any comparison. In 2025, that changed. SURMOUNT-5 was published. It was the first randomised head-to-head trial to compare tirzepatide and semaglutide injection in the same study. Randomised means people were assigned to one drug or the other by chance. There is no longer any need to guess. The direct comparison confirmed what the indirect data suggested: tirzepatide produces greater weight loss.

The comparison below draws on SURMOUNT-1, SURMOUNT-5, STEP 1, the SELECT cardiovascular outcomes trial, and the newer oral formulation studies — covering weight loss, side effects, heart outcomes, cost, and how to choose.

The weight loss numbers

In the SURMOUNT-1 trial, people taking tirzepatide at its highest dose lost an average of 20.9% of their body weight. The trial ran for 72 weeks in 2,539 participants without diabetes. To put that in concrete terms: for a 220 lb person, that's roughly 46 lbs. That is meaningfully larger than what any previous weight loss drug had achieved in clinical trials. The dual GIP+GLP-1 mechanism appears to produce stronger appetite suppression and a greater overall metabolic effect than GLP-1 alone.

In the STEP 1 trial, 1,961 participants took semaglutide injection for 68 weeks and lost an average of 14.9%. For the same 220 lb person, that's around 33 lbs. That is still a clinically meaningful result, and it represents a major advance over older treatments. But there is a real gap between 14.9% and 20.9%, about 6 to 7 percentage points. It shows up consistently across every study that has examined both drugs.

SURMOUNT-5 settled the indirect comparison debate definitively. In that direct head-to-head trial, people randomised to tirzepatide lost significantly more weight than those on semaglutide injection. That was roughly 47% more on a relative basis. This is not a marginal edge. It is a consistent, statistically significant difference. The trial only ran for 72 weeks, and it only measured weight outcomes. But on the primary question of which drug produces greater weight loss, the data is now clear.

Semaglutide now also comes in a daily pill form (oral Wegovy, 25mg, FDA-approved December 2025). In the OASIS 4 trial, people taking oral semaglutide lost an average of 13.6%. That is slightly less than the injection, but still a substantial result for a pill taken once daily rather than a weekly injection. This changes the cost and convenience calculation significantly.

These figures are trial averages across large populations. Individual results vary considerably. Some people lose far more, others less. It depends on starting weight, diet, activity level, and how well they tolerate stepping up to the full dose. The percentages give you the average from well-run studies, not a prediction for any individual.

Side effects: what you're actually getting into

Both drugs work by activating GLP-1 receptors in the gut and brain, so both share a similar side effect profile. Nausea, diarrhoea, vomiting and constipation are the most commonly reported issues, and they are real. This is not a category where either drug gets a clean bill of tolerability. What matters more is the pattern. For most people, stomach side effects are worst while the dose is being stepped up, typically the first 8 to 12 weeks. They improve substantially once you reach and stabilise on your maintenance dose. The step-up schedules for both drugs start low and rise slowly over several months, specifically to keep that disruption down.

Looking at the trial data, people on semaglutide reported higher nausea rates (around 44% in STEP 1) compared to people on tirzepatide (around 31% in SURMOUNT-1). Similar patterns showed up across diarrhoea, vomiting, and constipation. That said, these numbers come from different trials with different populations. This is not a controlled head-to-head comparison of side effects. SURMOUNT-5 didn't publish detailed side-effect breakdowns in the same way. The comparison below is indicative, not definitive.

The practical takeaway is that most people who stick with either drug find the side effects manageable, particularly after the initial adjustment period. A minority find them intolerable at higher doses and either stay at a lower maintenance dose or switch drugs. There is no reliable way to predict in advance which group you will fall into.

Figures from separate trials — SURMOUNT-1 (tirzepatide) and STEP 1 (semaglutide). These are not from a controlled head-to-head comparison and should be read as indicative.

The heart question — where semaglutide stands alone

This is the section that shifts the comparison significantly for a specific group of people. The SELECT trial enrolled 17,604 participants. All had overweight or obesity plus established heart disease, meaning a prior heart attack, stroke, or diagnosed heart condition. It followed them for approximately 40 months. The result: people taking semaglutide injection experienced a 20% reduction in major heart events compared to placebo. That is a reduction in actual heart attacks and strokes, not just a stand-in measurement.

No other weight loss drug has this level of heart outcome evidence. This is not a claim about weight loss or metabolic markers. It is a large randomised controlled trial showing that semaglutide reduces the rate at which people with existing heart disease have major cardiac events. The FDA approved Wegovy specifically for heart risk reduction on the basis of SELECT. That made it the first weight loss drug to carry that approved use.

Tirzepatide very likely has heart benefits too. The mechanism suggests it would, and early metabolic data is encouraging. But the large heart outcomes trial, SURPASS-CVOT, is still running as of mid-2026. For someone with existing heart disease who is deciding between these two drugs today, the SELECT data is a meaningful difference. The evidence exists for semaglutide. It does not yet exist for tirzepatide at the same scale.

Cost: the picture has changed

Both manufacturers now run self-pay savings programmes for their injections. Lilly's LillyDirect brings Zepbound down to $299–$449/mo a month without insurance, depending on the dose. Novo Nordisk's NovoCare Pharmacy brings Wegovy injection down to $349–$399/mo a month, also by dose. Zepbound's list price without that programme is $1,086/month. Wegovy's list price is $1,349/month. So on paper Wegovy still looks pricier, but the two self-pay ranges now overlap. Neither drug is affordable without either the savings programme or insurance coverage.

Oral Wegovy changed the calculation further. At its $149-per-month starting price self-pay, it is roughly 50% to 67% cheaper than Zepbound via LillyDirect. It is roughly 57% to 63% cheaper than Wegovy injection self-pay, depending on dose, and over 89% cheaper than Wegovy injection's list price. That is not a small difference. For most people without insurance coverage, it is the difference between a drug being financially accessible or not. The trade-off is that in clinical trials, people on oral semaglutide lost an average of 13.6%, versus 20.9% for tirzepatide injection. Whether that trade-off makes sense depends entirely on your financial situation and how much the additional weight loss matters to you.

Foundayo (orforglipron) received FDA approval in April 2026. It is also available at around $349 per month. That makes it another oral GLP-1 option in a similar price bracket, though with somewhat lower trial weight loss figures of 7.9–9.4%. The oral market is expanding, and prices are likely to come down further as competition increases.

Insurance coverage varies enormously. Many plans still exclude weight loss medications entirely. Where coverage does exist, copays can bring costs down dramatically. Oral Wegovy can reach as low as $25/month with insurance. If you have coverage, the cost comparison looks very different than it does at list price.

How to think about choosing between them

The right choice depends on individual medical history, risk factors, budget, and tolerance for injections. Here's how the data frames the decision.

If weight loss is the primary goal and injections are not a barrier, tirzepatide has the clearer edge. The SURMOUNT-5 head-to-head settled that argument. In clinical trials, people on tirzepatide lost roughly 6 to 7 percentage points more than those on semaglutide injection. The direct comparison confirmed that gap is real and statistically significant. For someone who wants to maximise the weight loss outcome from a once-weekly injection, the data points consistently in one direction.

If heart health is a significant concern, the SELECT trial data changes the conversation. That applies particularly where there is already a diagnosis of heart disease, a prior heart attack, or a prior stroke. Semaglutide injection is the only weight loss drug that has demonstrated a reduction in actual major heart events in a large outcomes trial. That is not a minor footnote. For someone in that situation, it is potentially the most important piece of data on this page. Tirzepatide may well show similar benefits when its own heart outcomes trial reports, but that data does not exist yet.

If cost is the dominant factor, the comparison shifts entirely. Oral Wegovy, from $149 per month, produced 13.6% weight loss. That is meaningfully less than tirzepatide injection, but still a substantial result, and it comes without a weekly needle. For someone who cannot afford $299+ per month, the choice between oral semaglutide and no treatment is straightforward. For someone comparing $149–$299 per month to $299–$449 per month, the question is different: is the additional 7 percentage points of weight loss worth the cost difference to them personally?

If injections are a hard barrier, whether from needle phobia, lifestyle or practicality, then both oral Wegovy and Foundayo become serious options. Both are daily pills in the $149–$349 range, and both represent a real advance in making GLP-1 therapy more accessible. The weight loss outcomes are lower than the injections. But for many people, being able to keep taking a daily pill outweighs a percentage-point difference in trial averages.