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Why am I not losing weight on Mounjaro or Wegovy?

GLP Guidebook teamUpdated 20 Oct 202614 sourcesWritten from published sources
What we checked14 sources, each one opened and linked to the sentence it supportsLast checked 20 Oct 2026 · Next review due 20 Oct 2027 · How we write
The short answer

Most people lose weight on Mounjaro (tirzepatide) or Wegovy (semaglutide), but not all. In the main UK-label trials, 4 to 11 in 100 on Mounjaro and about 1 in 6 on Wegovy didn't lose 5%. Type 2 diabetes can slow loss. Under 5% after 6 months (on Mounjaro, at the top tolerated dose) means a NICE review.

Before you go further
  • Mounjaro and Wegovy, like every GLP‑1 medicine, are prescription-only medicines in the UK.10
  • Never change your dose yourself. Your prescriber sets it.
  • Nothing here promises any result. The risks are in Guide 5: Side effects and risks.

How many people lose little or no weight?

In the main UK-label trials, 4 to 11 in 100 on Mounjaro and about 1 in 6 on Wegovy didn't lose 5%.1,3

SURMOUNT-1 followed 2,539 adults without diabetes for 72 weeks. On Mounjaro, 89 to 96 in 100 lost at least 5%, depending on dose. On the dummy, 28 in 100 did.1

In STEP 1, 84 in 100 on Wegovy 2.4 mg lost at least 5% by week 68. On the dummy, 31 in 100 did. About 10 in 100 were under 5% at 28 weeks. Of those, 4 in 10 got there by week 68.3 For a 100 kg (15 st 10 lb) person, 5% is 5 kg (11 lb).

Could the dose be the reason?

Possibly, because both medicines start low, and the UK labels don't count the first doses as maintenance doses, the doses people stay on.1,3

Mounjaro starts at 2.5 mg for 4 weeks, then 5 mg. It can rise in 2.5 mg steps, at least 4 weeks apart, up to 15 mg. The maintenance doses are 5, 10 and 15 mg.1 In SURMOUNT-1, average loss was 16.0% on 5 mg and 22.5% on 15 mg.1 More people stopped at higher doses because of stomach side effects. That was 2 in 100 on 5 mg and 4 in 100 on 15 mg, against under 1 in 100 on the dummy.1

Wegovy starts at 0.25 mg and rises over 16 weeks to 2.4 mg, to reduce stomach side effects.3 Tirzepatide reaches a steady level after 4 weeks of weekly doses.1 Our maintenance dose answer and Guide 6 cover the steps.

What else can slow weight loss?

Type 2 diabetes is the clearest factor, because people with diabetes lost less on both medicines in trials, and NICE says loss may be slower.1,3,7

In SURMOUNT-2, adults with type 2 diabetes lost 13.4% to 15.7% on Mounjaro over 72 weeks. The dummy group lost 3.3%.1 In STEP 2, people with diabetes lost 9.6% on Wegovy 2.4 mg, against 3.4%.3

The NHS lists other things that make it harder to stay a healthy weight. They include an underactive thyroid, Cushing's syndrome and polyendocrine metabolic ovarian syndrome (PMOS). The menopause and some steroids, antidepressants and beta blockers are also listed.8 It covers weight in general, not GLP‑1s.

Both UK labels report similar blood levels from the tummy, thigh or upper arm.1,3 The Wegovy needle has two caps, and the leaflet says that if you forget to remove both, you inject nothing.4

What happens if you've lost under 5% at 6 months?

NICE and the UK labels ask for a decision on carrying on when under 5% of starting weight is lost by 6 months.1,3,5,6

For Wegovy, NICE says to consider stopping after 6 months of treatment.6 For Mounjaro, the 6 months count from reaching the highest dose you tolerate. NICE then says to decide whether to continue.5 Details are in our NICE 5% rule post.

The MHRA says to get professional advice before any switch.10 In SURMOUNT-5, adults without diabetes lost 20.2% on tirzepatide and 13.7% on semaglutide over 72 weeks. It didn't test switching after a poor response.9

If weight stops falling after early loss, that is a plateau, covered in our plateau post.

What do people on Mounjaro and Wegovy report about slow or no weight loss?

From public patient forums: 12 Reddit threads in r/Zepbound, r/Mounjaro, r/OzempicForWeightLoss, r/WegovyWeightLoss, r/Wegovy and r/MounjaroUK, read in October 2026. Personal reports, not medical evidence.

What people describe

  • Matches the label Many say they felt little on the first doses and only noticed a change higher up. The UK labels list those first doses as starting doses, not maintenance doses.1,3
  • Matches the trials Several say slow starters went on to lose weight months later. In STEP 1, 4 in 10 people under 5% at 28 weeks reached it by week 68.3
  • Matches the trials A few replies say people with type 2 diabetes tend to lose less. The diabetes trials found the same.1,3
  • Not studied Many say semaglutide did little for them but tirzepatide worked, or the other way round. SURMOUNT-5 compared the two but didn't test switching after a poor response.9
  • Label says otherwise A few say changing injection site brought the effect back. Both UK labels report similar blood levels from the tummy, thigh or upper arm.1,3

Advice people share

  • Matches the label Most replies say the medicine works alongside eating less, not instead of it. The UK leaflet says Mounjaro is used with a reduced-calorie diet and more physical activity.2
  • Matches the NHS Several say to ask a GP about thyroid and hormone problems and other medicines. The NHS lists an underactive thyroid and some medicines among things that make it harder to stay a healthy weight, and says to speak to a GP for advice about such conditions.8
  • Matches the leaflet A few say to check the inner needle cap comes off. The Wegovy leaflet says that with both caps left on, you inject nothing.4
  • Label says otherwise Several posts describe counting pen clicks for in-between doses, splitting doses or adding extra ones. The UK label sets one Mounjaro dose a week. Doses rise in 2.5 mg steps at least 4 weeks apart, to 15 mg at most.1
The risks, in brief
  • Stomach effects. In the Mounjaro weight trials, 25 to 29 in 100 people felt sick (nausea), against 9 in 100 on a dummy injection. On Wegovy 2.4 mg it was 44 in 100, against 16 in 100.1,3
  • Higher doses. 2 in 100 on Mounjaro 5 mg and 4 in 100 on 15 mg stopped because of stomach effects, against fewer than 1 in 100 on the dummy.1
  • Gallbladder. Acute gallbladder disease affected 20 in 1,000 on Mounjaro, against 16 in 1,000 on the dummy. Gallstones were reported in 16 in 1,000 on Wegovy 2.4 mg.1,3
  • Pancreatitis (an inflamed pancreas) has been reported, including deaths, after Mounjaro was marketed.1
  • Pregnancy. Stop Mounjaro at least 1 month, and Wegovy 2 months, before a planned pregnancy.1,3
Full detail in our side effects guide →
Get help now: call 999 or go to A&E if:
  • a stomach ache came on very suddenly or is severe12
  • it hurts when you touch your stomach12
  • you're vomiting blood, or you have diabetes and you're vomiting12
Not sure? Use NHS 111.13 In Northern Ireland, use your GP's out-of-hours service.14

Get urgent medical attention for severe stomach pain that won't go away and may spread to your back, with or without being sick. The MHRA lists it as a warning sign of pancreatitis.11

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Related questions

What is the maintenance dose of Mounjaro? Can I get Mounjaro on the NHS? Can my GP prescribe Wegovy? When should I call 999 or 111 on a GLP-1?
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Sources

  1. Eli Lilly. Mounjaro KwikPen (tirzepatide) UK summary of product characteristics (SmPC), date of revision 29 Aug 2026, sections 4.2, 4.6, 4.8, 5.1 and 5.2. UK label. medicines.org.uk (emc)
  2. Eli Lilly. Mounjaro KwikPen (tirzepatide) UK patient information leaflet, last revised Aug 2026, section 1. UK label. medicines.org.uk (emc)
  3. Novo Nordisk. Wegovy FlexTouch (semaglutide) UK SmPC, date of revision 09/2026, sections 4.2, 4.6, 4.8, 5.1 and 5.2. UK label. medicines.org.uk (emc)
  4. Novo Nordisk. Wegovy FlexTouch (semaglutide) UK patient information leaflet, last revised 08/2026, instructions for use. UK label. medicines.org.uk (emc)
  5. NICE. Tirzepatide for managing overweight and obesity. Technology appraisal TA1026, recommendation 1.2 (published 23 Dec 2024). nice.org.uk
  6. NICE. Semaglutide for managing overweight and obesity. Technology appraisal TA875, recommendation 1.2 (published 8 Mar 2023). nice.org.uk
  7. NICE. Overweight and obesity management. Guideline NG246, medicines and surgery, recommendation 1.17.7 (published 14 Jan 2025). nice.org.uk
  8. NHS. Obesity: causes (page last reviewed 29 Apr 2026). nhs.uk
  9. Aronne LJ et al. Tirzepatide as compared with semaglutide for the treatment of obesity (SURMOUNT-5). N Engl J Med 2025;393(1):26-36. DOI 10.1056/NEJMoa2416394. PMID 40353578. Funded by Eli Lilly. PubMed
  10. MHRA. GLP-1 medicines for weight loss and diabetes: what you need to know (updated 5 Feb 2026), "Switching between GLP-1 medicines". gov.uk
  11. MHRA. MHRA updates guidance for GLP-1 prescribers and patients. Press release, 29 Jan 2026. gov.uk
  12. NHS. Stomach ache (page last reviewed 26 May 2023). nhs.uk
  13. NHS. When to call 999 (page last reviewed 3 Feb 2023). nhs.uk
  14. nidirect. GP out of hours service. nidirect.gov.uk

Last checked 20 Oct 2026 · Next review due 20 Oct 2027 · Report an error

How this answer was made. Written by the GLP Guidebook team from the sources above. It's general information, not medical advice. The 'What people report' section summarises public patient forum posts we read; it is not medical evidence, and we never pass on advice that goes against the label. Talk to a qualified doctor before starting, stopping or changing any medicine. How we write