Medication Comparisons

Weight Loss Medication Comparisons

Compare weight loss injections including Mounjaro, Wegovy, and Retatrutide to understand differences in results, pricing, and suitability.

Whether you are choosing your first weight-loss injection or wondering if you should switch, this is the medication comparisons hub for the three weight-loss injections most discussed in the UK — Mounjaro, Wegovy, and the investigational retatrutide. The aim is to help you understand how they compare on the things that matter, and to point you to the deeper guides for each pairing. LetsLoseWeight is an independent comparison site; we do not prescribe medication.

Quick orientation

Mounjaro (tirzepatide) Wegovy (semaglutide 2.4mg) Retatrutide
UK status Licensed for weight management (2023) Licensed for weight management (2021) Not licensed
Available in UK Yes, regulated pharmacies Yes, regulated pharmacies No (clinical trial only)
Manufacturer Eli Lilly Novo Nordisk Eli Lilly
Receptors targeted GIP, GLP-1 (dual) GLP-1 only GIP, GLP-1, glucagon (triple)
Pivotal trial weight loss ~20.9% at 15mg, 72 weeks ~14.9% at 2.4mg, 68 weeks ~24.2% at 12mg, 48 weeks (phase 2)
Typical UK private price £130–£300 per month £130–£300 per month No legitimate UK price
NHS access TA1026 — no 2-year cap TA875 — capped at 2 years None

The live comparison: Mounjaro vs Wegovy

The most important comparison for UK patients today is between Mounjaro and Wegovy — both are licensed, both available, both well-evidenced. The 2025 SURMOUNT-5 head-to-head trial showed greater average weight loss with tirzepatide than with semaglutide (Aronne et al., NEJM 2025).

That makes Mounjaro the default first-line private choice for many patients, all else being equal. Wegovy remains a strong option for those with specific reasons to prefer semaglutide — longer track record, lower headache frequency for some patients, or specific cost considerations.

For full detail, see our Mounjaro vs Wegovy UK guide and our best weight loss injection UK decision framework.

The aspirational comparison: licensed vs retatrutide

Retatrutide phase 2 data is striking — around 24% average weight loss at 12mg in 48 weeks. But:

  • Retatrutide is not licensed in the UK
  • No regulated UK pharmacy can supply it
  • The 24% figure is from phase 2 — phase 3 may show different results
  • No head-to-head trial with Mounjaro or Wegovy exists

This makes the retatrutide comparisons informational rather than decisional for most UK patients today. The relevant question is "which licensed medicine?" not "should I get retatrutide instead?"

For the dedicated comparisons:

Comparison by what you might value

If you want maximum average weight loss

Among available UK options: Mounjaro 15mg (~20.9% average weight loss in SURMOUNT-1).

Retatrutide phase 2 data suggests ~24%, but it's not legitimately available in the UK. Among licensed options, Mounjaro is the larger-effect choice.

If you want the longest track record

Wegovy (semaglutide). The molecule has been in widespread use in diabetes since 2017 (originally as Ozempic, also from Novo Nordisk). Long-term cardiovascular benefits are demonstrated in the SELECT trial (Lincoff et al., NEJM 2023).

If you want NHS access with no time cap

NHS Mounjaro under TA1026 does not carry the 2-year cap that NHS Wegovy under TA875 does. Eligibility is tighter for NHS Mounjaro than NHS Wegovy.

If you have type 2 diabetes

Both Mounjaro and Wegovy are licensed for type 2 diabetes (Mounjaro under that name; semaglutide as Ozempic). The choice depends on existing medication regimen and your diabetes team's preference. Retatrutide is also being studied separately for diabetes.

If you have established cardiovascular disease

Wegovy has the strongest published cardiovascular outcomes data via the SELECT trial. Mounjaro's cardiovascular outcomes are still being studied (the SURMOUNT-MMO trial).

If cost is the most important factor

Mounjaro and Wegovy are similarly priced privately. NHS access is dramatically cheaper for both, where available. For lowest private cost, see our cheapest Mounjaro UK and cheapest Wegovy UK guides.

Comparison by side-effect profile

The three medicines share the GLP-1-class profile dominated by gastrointestinal symptoms — nausea, diarrhoea, constipation, indigestion. Specific differences:

Mounjaro Wegovy Retatrutide (phase 2)
Headache Common Very common Common
Gallstones Uncommon Common Limited data
Hair loss Common Common Common
Skin hypersensitivity Common Uncommon Limited data
Heart rate increase Uncommon Uncommon Signal flagged for phase 3
Oral contraceptive interaction Specific SmPC warning Not warned Unknown

For dedicated lists, see our Mounjaro side effects, Wegovy side effects, and retatrutide side effects guides.

What's the same across all three

Despite the differences, the three medicines share a lot:

  • Subcutaneous, once-weekly injection delivered by pre-filled pen
  • Gradual dose-titration over multiple weeks to reduce side effects
  • Licensed indication for adults with overweight or obesity (when licensed)
  • Adjunct to lifestyle change, not a replacement for it
  • Class warning about thyroid C-cell tumours and MEN 2
  • Long-term treatment rather than a short course
  • Real cardiometabolic benefits beyond just weight loss
  • GLP-1 receptor activation as a core mechanism

What's different

Where they differ meaningfully:

  • Number of receptors targeted — single (Wegovy), dual (Mounjaro), triple (retatrutide)
  • Average weight loss — Wegovy < Mounjaro < retatrutide (phase 2), but cross-trial caveats apply
  • Side-effect distribution — gallstones more common with Wegovy, oral contraceptive warning specific to Mounjaro
  • NHS access criteria — different BMI/comorbidity thresholds and treatment caps
  • Manufacturer — Mounjaro and retatrutide both from Eli Lilly; Wegovy from Novo Nordisk
  • Track record length — semaglutide (Wegovy) longest; tirzepatide (Mounjaro) newer; retatrutide investigational

Frequently asked questions

Which one is "best"?
Among licensed UK options, Mounjaro produces the largest average weight loss. But "best" depends on what you weight — track record, cost, NHS access, side effects, prescriber preference. See our best weight loss injection UK guide.

Should I wait for retatrutide?
Probably not. There's no published date for retatrutide UK approval, the wait is likely to be measured in years, and the medicines that exist now produce real weight loss. You can switch later if and when retatrutide is approved.

Can I take more than one of these at once?
No. Combining medicines that act on overlapping receptors risks severe side effects. Switching means stopping one before starting another, with the appropriate washout.

Are these "diabetes drugs" being used off-label for weight loss?
Wegovy and Mounjaro are specifically licensed for weight management, not just diabetes. Ozempic (also semaglutide) is licensed only for diabetes and should not be used for weight loss in the UK.

What about Saxenda or other older GLP-1 medicines?
Saxenda (liraglutide) is also licensed for weight management in the UK but is daily-injection (vs once-weekly) and shows lower average weight loss than the medicines above. It is increasingly an older-generation option.

Next steps

Use the comparisons below to dive in:

Sources

This guide is for general information only and is not a substitute for professional medical advice. The right medicine for you is a clinical decision with a qualified prescriber.

Get weekly weight loss tips

Join our newsletter for provider updates, expert guidance, and exclusive offers — no spam.

Subscribe free
Back to Prices
Weight Loss Medication Comparisons UK: Hub Guide | LetsLoseWeight