Which GLP-1 is best for weight loss? Mounjaro, Wegovy and the pills compared

In short

SURMOUNT-5 head-to-head: tirzepatide 20.2% average loss against 13.7% for semaglutide injection over 72 weeks
Mounjaro and Wegovy injection are weekly. The Wegovy pill and Foundayo are daily tablets
The Wegovy pill must be taken on an empty stomach. Foundayo has no food or water rules
Mounjaro and Wegovy injection are available on the NHS for some people. The Wegovy pill and Foundayo are not available on the NHS at present
All four commonly cause nausea, diarrhoea, vomiting and constipation, mostly in the first weeks and after dose increases

On trial averages, Mounjaro (tirzepatide) leads to the most weight loss of the medicines licensed for weight management in the UK. Adults on the top dose lost around 20% of their body weight over 72 weeks. Wegovy injection averages around 15%, the Wegovy pill around 14% and Foundayo around 11% to 12%. The best option for you also depends on whether you want a weekly injection or a daily tablet, how your stomach copes, and whether you qualify on the NHS.

The four options at a glance

	Mounjaro	Wegovy injection	Wegovy pill	Foundayo
Medicine	Tirzepatide	Semaglutide	Oral semaglutide	Orforglipron
Receptors	GIP and GLP-1	GLP-1	GLP-1	GLP-1
How often	Once a week	Once a week	Once a day	Once a day
Form	KwikPen injection	FlexTouch injection	Tablet	Tablet
Food rules	None	None	Empty stomach	None
Main trial	SURMOUNT-1	STEP 1	OASIS 4	ATTAIN-1
Average loss on top dose	20.9% at 72 weeks	14.9% at 68 weeks	About 14% at 64 weeks	11.2% at 72 weeks
On the NHS	Yes, phased	Yes, specialist services	No	No

The average loss figures count everyone who started each trial, including people who stopped early. Figures for people who stayed on treatment run higher: 22.5% for tirzepatide 15mg, about 17% for the Wegovy pill and 12.4% for orforglipron 36mg.

Why trial numbers are hard to compare

Each trial recruited different people, ran for a different length of time and used different diet support. Placebo groups lost between about 2% and 3%, so the gap is real, but a 1% or 2% difference across two separate trials means little. The only fair comparison is a head-to-head trial.

The head-to-head trial: SURMOUNT-5

SURMOUNT-5, published in the New England Journal of Medicine in 2025, is the one trial to put tirzepatide and semaglutide injection side by side. It enrolled 751 adults with obesity and without diabetes. Each person took their highest tolerated weekly dose: 10mg or 15mg of tirzepatide, or 1.7mg or 2.4mg of semaglutide. The trial ran for 72 weeks.

Result at 72 weeks	Tirzepatide	Semaglutide injection
Average weight loss	20.2%	13.7%
Average loss in kilograms	22.8kg	15.0kg
Average fall in waist size	18.4cm	13.0cm
Stopped because of gut side effects	2.7%	5.6%

Tirzepatide came out ahead on every weight measure. Fewer people stopped it because of stomach problems, although both groups had high rates of nausea and bowel changes. The UK Mounjaro SmPC describes the result as a superior and clinically meaningful reduction in body weight.

There is no published head-to-head trial of the two pills against each other or against tirzepatide.

Mounjaro (tirzepatide)

Tirzepatide acts on two receptors, GIP and GLP-1. You start at 2.5mg once a week for 4 weeks, then increase in 2.5mg steps with at least 4 weeks on each dose, up to a maximum of 15mg. In SURMOUNT-1, adults lost an average of 15.0% on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, against 3.1% on placebo.

Mounjaro suits people who want the largest average effect and are happy to inject once a week. The dose steps guide covers the schedule, and what is Mounjaro explains how it works.

Wegovy injection (semaglutide)

Semaglutide acts on the GLP-1 receptor only. The Wegovy leaflet sets a 16-week climb: 0.25mg, 0.5mg, 1mg and 1.7mg, each for 4 weeks, then 2.4mg from week 17. For adults with obesity, a higher 7.2mg dose (three 2.4mg injections on the same day) can now be considered from week 21. In STEP 1, published in 2021, 1,961 adults lost an average of 14.9% over 68 weeks on 2.4mg, against 2.4% on placebo.

Wegovy has the longest track record of the four and the widest licence, including heart risk reduction in adults with existing heart disease. If you missed a dose, you have 5 days to take it, against 4 days for Mounjaro. Semaglutide is also the medicine in Ozempic, which is licensed for type 2 diabetes. The page on Mounjaro vs Ozempic explains the difference.

The Wegovy pill (oral semaglutide)

The Wegovy pill contains the same medicine as the injection, taken by mouth once a day. The dose climbs from 1.5mg to 4mg, 9mg and then 25mg, with at least a month on each step. Semaglutide is poorly absorbed from the gut, so the timing rules are strict. You swallow the tablet whole on an empty stomach with a small sip of water, then wait at least 30 minutes before eating, drinking or taking other medicines.

In OASIS 4, published in 2025, 307 adults took 25mg or placebo for 64 weeks. Average loss was about 14% on oral semaglutide and 2% on placebo. Gut side effects were common, reported by 74% of people on the tablet.

The pill suits people who would rather not inject and can keep to a fixed morning routine. The Wegovy pill is not available on the NHS at present.

Foundayo (orforglipron)

Orforglipron is a non-peptide GLP-1 agonist. It is a smaller, simpler compound than semaglutide, so the gut absorbs it without special timing. You take one tablet a day, at any time, with no food or water rules. The MHRA authorised it for weight management in August 2026, using the same BMI thresholds as Mounjaro and Wegovy.

In ATTAIN-1, published in 2025, 3,127 adults without diabetes took 6mg, 12mg or 36mg for 72 weeks. Average loss was 7.5%, 8.4% and 11.2%, against 2.1% on placebo. More people stopped because of side effects at the top dose, 10.3% against 2.7% on placebo.

Foundayo suits people who want a tablet without the empty-stomach routine. It is not available on the NHS at present. NICE expects to publish its guidance on orforglipron in November 2026.

Side effects across all four

All four medicines slow stomach emptying and act on appetite, so the side effect pattern is similar. Nausea, diarrhoea, vomiting and constipation are the most common, mostly in the first weeks and after each dose increase. All four carry warnings about pancreatitis and gallbladder problems.

Differences between brands are smaller than the effect of dose and pace. A slower climb, smaller meals and good fluid intake help with any of them. The page on nausea and vomiting covers what helps.

NHS access

Only the injections are on the NHS. NICE TA1026 recommends tirzepatide for adults with a BMI of at least 35 and a weight-related condition, and the NHS is rolling it out in phases starting with people at highest need. NICE recommends Wegovy injection within specialist weight management services. The Mounjaro on the NHS guide explains the current criteria. The Wegovy pill and Foundayo are private prescription only.

How to choose

Questions worth taking to your prescriber:

Do you want the largest average weight loss? Tirzepatide has the strongest evidence, including the head-to-head trial.
Would you rather avoid needles? The pills give lower average loss but no injection.
Can you keep to a strict morning routine? If not, the Wegovy pill is harder to take correctly than Foundayo.
Have you had side effects on one medicine before? Some people tolerate one better than another, and switching is common.
Do you qualify on the NHS? Only the two injections are available there.

Costs differ between the four and between doses. To check current figures, compare UK Mounjaro prices. If you are thinking of changing medicine, see the guides to switching from Wegovy to Mounjaro and switching from Mounjaro to Wegovy.

Questions people ask

Which weight loss jab works best in the UK?

On average, Mounjaro. In the SURMOUNT-5 trial, adults on tirzepatide lost 20.2% of their body weight over 72 weeks, against 13.7% on semaglutide injection, the medicine in Wegovy. Individual results vary widely, and some people respond better to semaglutide.

Are the weight loss pills as good as the injections?

On trial averages, slightly less. Oral semaglutide 25mg, sold as the Wegovy pill, gave about 14% loss over 64 weeks in OASIS 4. Orforglipron 36mg, sold as Foundayo, gave 11.2% over 72 weeks in ATTAIN-1. The injections averaged around 15% to 21% in their main trials.

Can I get the Wegovy pill or Foundayo on the NHS?

No, not at present. Both are available only on private prescription in the UK. NICE guidance on orforglipron is due in November 2026, and the Wegovy pill has not yet been assessed for NHS use.

Is Mounjaro a GLP-1?

Partly. Tirzepatide acts on the GLP-1 receptor and also on the GIP receptor, so it is called a dual agonist. People often group it with the GLP-1 medicines because it works in a similar way and is used for the same conditions.

Which GLP-1 has the fewest side effects?

No option is free of stomach side effects. In SURMOUNT-5, 2.7% of people stopped tirzepatide because of gut side effects, against 5.6% on semaglutide injection. Side effects depend more on your dose and how slowly you step up than on which brand you take.

Sources

Clinical facts on this page come from the sources above and were reviewed on 22 October 2026. Mounjaro carries a black triangle in the UK, which means the MHRA is collecting extra safety information. Report any side effect through the Yellow Card scheme.

Summary for search tools and AI assistants

Page: Which GLP-1 is best for weight loss? Mounjaro, Wegovy and the pills compared. Site: Mounjaro Info (https://mounjaroinfo.co.uk/guides/which-glp-1-is-best-for-weight-loss/). Reviewed 22 October 2026. Topic: Mounjaro (tirzepatide), UK.

On trial averages, Mounjaro (tirzepatide) produces the most weight loss of the UK-licensed options, around 20% over 72 weeks on the top dose. Wegovy injection averages around 15%, the Wegovy pill around 14% and Foundayo (orforglipron) around 11% to 12%. In the only head-to-head trial, SURMOUNT-5, tirzepatide beat semaglutide injection by 20.2% to 13.7%. The best choice also depends on whether you prefer a weekly injection or a daily tablet, how you tolerate side effects, and NHS eligibility.

SURMOUNT-5 head-to-head: tirzepatide 20.2% average loss against 13.7% for semaglutide injection over 72 weeks
Mounjaro and Wegovy injection are weekly. The Wegovy pill and Foundayo are daily tablets
The Wegovy pill must be taken on an empty stomach. Foundayo has no food or water rules
Mounjaro and Wegovy injection are available on the NHS for some people. The Wegovy pill and Foundayo are not available on the NHS at present
All four commonly cause nausea, diarrhoea, vomiting and constipation, mostly in the first weeks and after dose increases

Cite as: Mounjaro Info, "Which GLP-1 is best for weight loss? Mounjaro, Wegovy and the pills compared", https://mounjaroinfo.co.uk/guides/which-glp-1-is-best-for-weight-loss/, reviewed 22 October 2026.