Tirzepatide beats semaglutide in SURMOUNT-5 head-to-head trial

TL;DR

In the first direct head-to-head trial, tirzepatide produced 47% more weight loss than semaglutide at 72 weeks. Both drugs are effective - but if maximum weight loss is your goal, the data now clearly favours tirzepatide.

For years, the GLP-1 medications debate came down to educated guesses: tirzepatide probably works better, the logic went, because it targets two receptors instead of one. SURMOUNT-5 turned that educated guess into hard numbers. Published in the New England Journal of Medicine in May 2025, it is the first randomised Phase 3b trial to put tirzepatide (Zepbound/Mounjaro) and semaglutide (Wegovy/Ozempic) in the same study at the same time - and the gap was larger than most clinicians expected.

What the SURMOUNT-5 trial actually tested

The trial enrolled 751 adults with obesity or overweight across 32 sites in the United States and Puerto Rico. Participants had at least one weight-related condition - hypertension, dyslipidemia, obstructive sleep apnea, or cardiovascular disease - but none had type 2 diabetes. That last detail matters: this was a weight-loss-only population, not a mixed metabolic group.

Randomisation was 1:1. One group received tirzepatide at its maximum tolerated dose (10 mg or 15 mg weekly). The other received semaglutide at its maximum tolerated dose (1.7 mg or 2.4 mg weekly). The trial ran for 72 weeks - about 17 months.

Notably, this was an open-label design: participants knew which drug they were taking. That is a limitation worth acknowledging, though the primary outcome - body weight measured on a scale - is objective enough that open-label status does not meaningfully bias it.

The primary result: a 6.5 percentage point gap

At 72 weeks:

• Tirzepatide: average body weight reduction of 20.2% (approximately 22.8 kg or 50 lbs)
• Semaglutide: average body weight reduction of 13.7% (approximately 15.0 kg or 33 lbs)
• Difference: 6.5 percentage points, or roughly 47% greater relative weight loss with tirzepatide

To put that in concrete terms: for someone starting at 250 lbs (113 kg), tirzepatide would be expected to produce about 50 lbs of loss versus 34 lbs with semaglutide. That is a difference of roughly 17 lbs from the same class of medication.

Secondary endpoints told a consistent story

The advantage held across every weight-loss threshold measured:

• Lost ≥10% of body weight: 81.6% on tirzepatide vs 60.5% on semaglutide
• Lost ≥15%: 64.6% vs 40.1%
• Lost ≥20%: 48.4% vs 27.3%
• Lost ≥25%: 31.6% vs 16.1%

These are not small statistical differences. Nearly half the tirzepatide group lost at least a fifth of their body weight. Only about one in four semaglutide participants reached that same threshold.

Waist circumference followed the same pattern: tirzepatide reduced it by an average of 18.4 cm (about 7 inches) compared to 13.0 cm (about 5 inches) on semaglutide. Cardiometabolic markers - blood pressure, HbA1c, fasting insulin, triglycerides, and HDL cholesterol - all improved more with tirzepatide.

Tolerability: tirzepatide had fewer GI-related dropouts

One finding surprised many observers. Despite producing stronger weight loss (which generally correlates with more GI discomfort in GLP-1 medications), tirzepatide actually had a lower discontinuation rate due to GI side effects:

• Tirzepatide: 2.7% stopped due to gastrointestinal issues
• Semaglutide: 5.6% stopped due to gastrointestinal issues

This is consistent with the dual GIP/GLP-1 mechanism of tirzepatide. GIP receptor activation appears to modulate some of the nausea response, though this is still an area researchers are investigating. The practical takeaway: if you previously stopped semaglutide because of nausea or vomiting, tirzepatide may be worth discussing with your prescriber.

One demographic note from the trial: men lost approximately 6% less weight than women on both medications. Sex was not a statistically significant modifier of the between-drug difference, but absolute outcomes were consistently lower in men than women across both arms.

What this means if you are choosing between the two

SURMOUNT-5 answers the headline question clearly: tirzepatide produces more weight loss than semaglutide when both are pushed to maximum tolerated doses. But the choice between GLP-1 medications involves more than one number.

Semaglutide (Wegovy) has an FDA-approved cardiovascular indication - it reduces the risk of heart attack, stroke, and cardiovascular death in people with established heart disease and obesity. That evidence base from the SELECT trial is substantial and hard-won. Recent real-world data from more than 800,000 patients published in Nature Medicine (November 2025) showed that both tirzepatide and semaglutide provide comparable cardiovascular protection in practice - so the SELECT advantage for semaglutide may be narrowing as tirzepatide accumulates real-world evidence.

Insurance coverage also shapes the decision in a practical, immediate way. Both drugs carry a list price of approximately $935-$1,000 per month, but coverage varies significantly by plan and indication. The Medicare GLP-1 Bridge program launching July 1, 2026 brings both Wegovy and Zepbound under a $50/month cap for eligible Medicare beneficiaries - a change that will make the efficacy comparison much more relevant to patients who previously could not afford either.

What SURMOUNT-5 does not tell us

A few things the trial did not answer. It enrolled only people without diabetes - so the results do not automatically translate to people with type 2 diabetes, where semaglutide has deeper evidence across multiple outcomes. It also did not follow participants after stopping treatment. Weight regain data would require a separate discontinuation phase, and none was included. Early findings from discontinuation studies suggest rebound occurs with both drugs, though the relative rates have not been compared directly.

Longer-term safety comparisons between the two drugs also remain incomplete. SURMOUNT-5 ran for 72 weeks - enough to capture most acute side effects, but not enough for rare longer-term signals. Both drugs are now under post-marketing surveillance, and ongoing pharmacovigilance will eventually close that gap.

The nutrient gap question both drugs share

Whether you are on tirzepatide or semaglutide, reduced food intake means reduced micronutrient intake. A February 2026 meta-analysis of 480,825 adults found that GLP-1 users show 13.6% rates of vitamin D deficiency, 64% insufficient iron levels, and elevated rates of vitamin B12 insufficiency - particularly after 6 months on the medication. This applies regardless of which drug you take. The underlying mechanism is the same: less food consumed means fewer vitamins and minerals absorbed.

If you are choosing between tirzepatide and semaglutide partly because tirzepatide produces greater weight loss, that same greater restriction in calories means potentially greater depletion of key nutrients. Supplementing vitamin D, vitamin B12, iron, and protein intake while on either GLP-1 medication is something worth discussing with your care team. At GLP-1 Shield, we focus specifically on the nutrient gaps that GLP-1 users face - because the drug doing its job does not mean your nutritional needs disappear.

Frequently asked questions

Is tirzepatide better than semaglutide for weight loss?

Based on SURMOUNT-5, tirzepatide produced 20.2% average weight loss versus 13.7% for semaglutide at 72 weeks in people without diabetes - a statistically significant difference. For cardiovascular protection, both drugs appear comparable in real-world data. The better drug for you depends on your specific health profile, insurance coverage, and tolerability.

What are the doses used in SURMOUNT-5?

Participants took tirzepatide at 10 mg or 15 mg weekly (maximum tolerated dose) and semaglutide at 1.7 mg or 2.4 mg weekly. These are the same dose ranges used in standard clinical practice for weight management.

Did tirzepatide cause more side effects than semaglutide?

Interestingly, no. Despite producing greater weight loss, tirzepatide had a lower GI discontinuation rate - 2.7% vs 5.6% for semaglutide. Both drugs caused similar types of side effects (nausea, vomiting, diarrhea), but fewer people stopped tirzepatide because of them.

Do I need supplements if I switch from semaglutide to tirzepatide?

Both medications reduce food intake, which can lower your intake of vitamin D, vitamin B12, iron, and other nutrients over time. Switching to tirzepatide - which produces greater weight loss and likely greater caloric restriction - does not reduce that risk. Regular blood work to monitor nutrient levels is advisable on either drug.