SURMOUNT-5 Tirzepatide vs Semaglutide Weight Loss Results (October 2026)

01 · The verdict

SURMOUNT-5 verdict: tirzepatide lost more weight on average

Tirzepatide produced a larger average weight loss than semaglutide 2.4mg in SURMOUNT-5: 20.2% versus 13.7% of body weight over 72 weeks.¹⁵ That is a gap of 6.5 percentage points.

The same evidence says the headline number should not make the decision alone. Both are effective, licensed treatments, and which suits you depends on your health profile, tolerance and prescriber advice.¹⁵ Our wider guides cover tirzepatide vs semaglutide superiority and the head-to-head weight loss evidence in more depth.

02 · Side by side

Tirzepatide vs semaglutide at a glance

You can see current options on the Mounjaro pen page and the Wegovy pen page. All six Mounjaro doses are in stock; for Wegovy, check availability at the time of order.

03 · Decision factors

Which option suits whom?

There is no single right answer: which suits you depends on your health profile, tolerance and prescriber advice, not the headline number alone. Semaglutide 2.4mg suits people whose prescriber prefers it, or who already do well on it. Neither choice is permanent: your prescriber can review the plan as you go.

Four factors usually decide it:

• Your health profile: other conditions and medicines your prescriber needs to weigh.
• Tolerance: how you cope with digestive effects at each dose step.
• Experience so far: someone already responding well to Wegovy has less reason to change than someone who has plateaued.
• Cost and supply: compare live prices and availability when you order.

If you want a prescriber's view, our free online consultation is reviewed by a GPhC-registered prescriber, with no charge and no obligation. Browse all weight loss treatments to see the full range.

04 · SURMOUNT-5 figures explained

What the SURMOUNT-5 numbers mean in kilograms

SURMOUNT-5 reported averages of 20.2% body-weight loss on tirzepatide and 13.7% on semaglutide 2.4mg over 72 weeks.¹⁵ Percentages are easier to apply once you convert them to your own starting weight.

As a worked example, for someone starting at 100 kg, 20.2% is about 20 kg and 13.7% is about 14 kg. At 120 kg the same percentages are roughly 24 kg and 16 kg. These are straight arithmetic on trial averages, not predictions. Our kg comparison guide and percentage comparison go further.

An average hides a wide spread. Some people lose more than the mean and some less, so trial averages do not predict your own result. Treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.²

05 · Comparing across trials

Why other trial numbers are not a head-to-head

Only SURMOUNT-5 supports a direct tirzepatide-versus-semaglutide comparison, because both drugs were tested in the same trial. Results from different trials should not be lined up against each other as if they were.

For reference, each medicine has its own pivotal trial. In SURMOUNT-1, 2,539 adults on tirzepatide lost on average 15% of body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, compared with 3.1% with lifestyle changes alone.² In STEP 1, adults on semaglutide 2.4mg lost on average 14.9% of body weight over 68 weeks, compared with 2.4% on placebo.⁹

Those are separate studies with their own designs, so use them to understand each drug, and use SURMOUNT-5 to compare the two. Our SURMOUNT-1 guide covers the tirzepatide trial in full. A diabetes-focused comparison is in our SURPASS-2 results guide.

06 · Why tirzepatide may differ

How the two medicines work differently

Tirzepatide activates two natural gut-hormone receptors at once, GIP and GLP-1, whereas semaglutide is a single-action GLP-1 medicine.¹ Together these actions help regulate appetite, slow how quickly the stomach empties and improve the way the body responds to insulin.

In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹

Results with either medicine still depend on eating less and moving more.

07 · Side effects compared

Side effects: what to expect on tirzepatide

Side effects on tirzepatide are mostly digestive. The most common, affecting more than 1 in 10 people, are nausea, diarrhoea, vomiting, constipation and abdominal discomfort.¹ They are most likely when starting treatment or moving up a dose, and for most people they ease within days to a few weeks as the body adjusts.

In the weight-management trials supporting the licence, nausea was reported by 24.6% of people on 5mg, 29.0% on 10mg and 28.0% on 15mg, compared with 8.5% on placebo. Diarrhoea was reported by 18.7%, 20.8% and 22.5% respectively, compared with 7.8% on placebo.¹ These effects became less frequent over time. Stopping permanently because of stomach side effects affected 1.9% of people on 5mg, 3.3% on 10mg and 4.3% on 15mg, against 0.5% on placebo.¹

Hair loss was reported by 4.9% of people on tirzepatide against 1.0% on placebo, and injection-site reactions by 8.0% against 1.8%.¹

Get medical help straight away for severe, persistent stomach pain that may spread to your back, pain in the upper right abdomen with fever or yellowing of the skin or eyes, or swelling of the face or throat with difficulty breathing.¹³ You can report any suspected side effect through the Yellow Card scheme.¹⁹

08 · Muscle, face and hair

Muscle, face and hair changes

Protecting lean mass matters on either medicine: adequate protein, resistance exercise and a pace of loss guided by your prescriber rather than maximum speed.

"Ozempic face" is not a drug effect. It is what losing a significant amount of weight quickly can do to facial volume on any method, including diet or surgery, and the same applies to loose skin. Skin commonly adapts gradually after weight stabilises.

Temporary hair shedding is a recognised side effect, linked to rapid weight loss itself rather than a direct drug effect. For most people it settles as weight stabilises, and balanced nutrition helps.¹

09 · Switching and safety

Switching between semaglutide and tirzepatide

There is no licensed direct conversion between semaglutide and tirzepatide, so any switch happens under prescriber supervision. Typically the previous medicine is stopped, a washout interval is observed, and Mounjaro is started at a dose your prescriber judges appropriate, often the 2.5mg starting dose.

Never run two GLP-1 medicines together. Mounjaro must also not be combined with unlicensed "research" peptides, such as retatrutide, which has no UK licence, or with compounded copies. These combinations have no safety data and no regulated supply chain, and anything promising faster results outside a licensed pathway is a warning sign.

Ozempic is semaglutide licensed for type 2 diabetes, not a UK weight-loss medicine. The licensed weight-management options are Mounjaro (tirzepatide) and Wegovy (semaglutide 2.4mg), so a regulated UK pharmacy will not supply Ozempic for weight loss. Our tirzepatide vs semaglutide guide covers the practical differences.

10 · Getting treatment

How to start treatment with us

Mounjaro is a prescription-only medicine, supplied after an online consultation reviewed by a GPhC-registered prescriber. We supply Mounjaro through official LillyDirect supply, with genuine KwikPens.

• Free online consultation: a short health questionnaire, with no charge and no obligation.
• Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full.
• Dispatch and delivery: same-day dispatch when ordered by 3pm, then free next-day tracked delivery in temperature-controlled packaging.

NHS access to Mounjaro is being phased in over several years, so many people who meet the licensed criteria choose regulated private treatment rather than waiting. Mounjaro (tirzepatide) is used alongside a reduced-calorie diet and increased physical activity. Individual results vary.

11 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹