Retatrutide vs Mounjaro vs Wegovy: How the GLP-1 Weight Loss Injections Compare in 2026

Where things stand right now#

If you've been following the weight loss medication space in 2026, you'll know the landscape has shifted considerably. Mounjaro (tirzepatide) is now firmly established as the most potent licensed weight loss injection available in the UK. Wegovy (semaglutide) remains a popular and well-evidenced option. And two newer drugs, retatrutide and CagriSema, are generating significant interest after impressive clinical trial data.

So which actually works best? And what's realistically available to you right now in the UK? This article works through the evidence for each, explains the key differences, and helps you figure out which direction makes sense.

At a glance: how they compare#

The headline: Mounjaro is currently the most effective licensed option, but both retatrutide and CagriSema have shown impressive results in trials. Neither is available in the UK yet.

How each medication works#

Mounjaro (tirzepatide)#

Mounjaro works by mimicking two hormones simultaneously: GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). Both play roles in regulating appetite, blood sugar, and digestion. By targeting both receptors, Mounjaro produces stronger appetite suppression than a single-hormone approach. It's this dual action that helps explain why it consistently outperforms older GLP-1 medications in head-to-head trials.

It's given as a once-weekly subcutaneous injection, starting at 2.5mg and increasing gradually up to 15mg as tolerated. The slow dose escalation matters: it significantly reduces the risk of nausea and other GI side effects during the adjustment period.

Wegovy (semaglutide)#

Wegovy contains semaglutide, which acts on GLP-1 receptors only. It's well-established, with years of real-world data behind it, and has been shown in the SELECT trial to reduce the risk of major cardiovascular events in people with obesity and existing heart disease. That cardiovascular benefit is something the other medications in this comparison don't yet have licensed approval for.

Wegovy is available as a weekly injection or, more recently, as daily oral tablets. The injection doses range from 0.25mg up to 2.4mg. Oral semaglutide (Wegovy tablets) offers an alternative for people who prefer to avoid injections entirely.

CagriSema#

CagriSema combines two active ingredients: cagrilintide (an amylin analogue) and semaglutide. Amylin is a hormone produced by the pancreas that works alongside insulin to control appetite and slow gastric emptying. Adding it to semaglutide creates a different dual-action approach to Mounjaro, targeting appetite through two separate pathways rather than GLP-1 and GIP.

The REDEFINE 4 trial, which directly compared CagriSema against Mounjaro 15mg over 84 weeks, found average weight loss of 23.0% with CagriSema versus 25.5% with Mounjaro. CagriSema didn't meet its pre-specified non-inferiority endpoint, meaning it didn't prove it was as effective as Mounjaro in that trial. Mounjaro won, though the gap was closer than many expected.

Retatrutide#

Retatrutide is a triple receptor agonist, acting on GLP-1, GIP, and GCG (glucagon) receptors. The addition of glucagon receptor activity increases energy expenditure, not just appetite suppression, which theoretically gives it an additional mechanism for weight loss. Phase 2 data showed approximately 24% body weight reduction at 48 weeks, which is remarkable for that timeframe. Phase 3 trials were due to conclude in mid-2026, with regulatory submissions expected afterwards.

It's worth noting that Phase 2 results don't always translate directly to Phase 3 outcomes, and we don't yet have the long-term safety data that exists for both tirzepatide and semaglutide.

Weight loss results in detail#

Let's look at what the best available clinical evidence shows for each medication.

The SURMOUNT-1 trial for Mounjaro showed up to 22.5% mean body weight reduction over 72 weeks at the 15mg dose. This was in adults without type 2 diabetes. A direct head-to-head with Wegovy (the SURMOUNT-5 trial) found Mounjaro produced significantly greater weight loss than semaglutide 2.4mg over the same period.

Wegovy's STEP-1 trial showed approximately 15% mean body weight reduction over 68 weeks. The SELECT trial added important cardiovascular outcome data. Real-world data from the SHAPE study has also confirmed that tirzepatide consistently outperforms semaglutide in patients without type 2 diabetes.

For CagriSema, the REDEFINE-1 trial showed approximately 23% weight loss over 68 weeks, which is genuinely impressive. However, REDEFINE 4's head-to-head result (23.0% vs 25.5% in favour of Mounjaro) means CagriSema, even if it eventually gets licensed, may not displace Mounjaro as the top option for most people.

Retatrutide's Phase 2 data showed around 24% body weight reduction at 48 weeks in the highest dose group. If Phase 3 confirms this, it would be competitive with or exceed Mounjaro's results. Phase 3 completion and subsequent regulatory review (first by the FDA, then EMA and MHRA) means UK availability is realistically 2027 at the earliest, and likely later.

Side effects and tolerability#

All of these medications share a broadly similar side effect profile because they all slow gastric emptying to varying degrees. The most common issues are:

• Nausea (most common, especially during dose increases)
• Vomiting
• Diarrhoea or constipation
• Reduced appetite beyond what's intended
• Occasional fatigue or dizziness

Mounjaro and Wegovy both have extensive real-world tolerability data. The majority of people experience some nausea early on, particularly during dose escalation, but this typically settles within a few weeks. The slow titration schedule for Mounjaro (increasing by one dose step every four weeks) is specifically designed to minimise this.

CagriSema appears to have a broadly similar side effect profile to semaglutide, though nausea rates were slightly higher in the REDEFINE trials. For retatrutide, Phase 2 data showed comparable GI side effects to other agents in this class.

For people with a history of significant GI conditions, or who have struggled with nausea on GLP-1 medications previously, this is worth discussing with a clinician before starting. It may affect which medication (and which dose escalation pace) is most appropriate for you.

UK availability and cost#

This is where things get very practical, and it's where a lot of comparison articles fall short.

Mounjaro is currently the only one of these four that combines strong efficacy data with full UK licensing. It received NICE technology appraisal approval (TA1026) for weight management in England. Access via the NHS is possible but comes with strict eligibility criteria and, in many areas, significant waiting times through specialist weight management services. Most people accessing Mounjaro privately do so through online pharmacies or private clinics.

At Totiva, Mounjaro is available with transparent per-pen pricing starting at £136.88 for 2.5mg, rising to £268.88 for the 15mg maintenance dose. There's no subscription required, and you only pay after a clinician has assessed your suitability. You can explore the weight loss treatments available at Totiva to see full pricing and eligibility details.

Wegovy is also licensed in the UK and available through NHS and private routes. NICE TA875 covers semaglutide for weight management. At Totiva, Wegovy injections start at £92.88 per pen (for the lower doses) up to £188.88 for the 2.4mg maintenance dose. Wegovy tablets (oral semaglutide) start at £99.00 for 30 tablets, which some people find more convenient than weekly injections.

CagriSema is not licensed in the UK and is not commercially available here. Regulatory submissions to the EMA and MHRA had not been filed as of mid-2026. Realistically, if Phase 3 data is strong, UK patients might see it available privately by late 2027 or 2028, though this timeline is speculative.

Retatrutide is at an earlier stage. Phase 3 trials were completing in 2026, meaning regulatory review hasn't begun. UK licensing is probably at least two to three years away. Anyone offering retatrutide in the UK right now is operating outside regulated channels, and that's a significant safety concern.

What about stopping? The weight regain question#

One thing most comparison articles overlook is what happens when you stop. It's an important question because all of these medications work by suppressing appetite through hormonal signalling. When you stop, those effects stop too.

Studies following people who discontinued tirzepatide or semaglutide show meaningful weight regain over the following 12 months, typically recovering around half the lost weight within a year. This isn't a reason to avoid these medications, but it does mean treatment is often long-term, and realistic expectations are important.

Some people choose to stay on a maintenance dose indefinitely. Others reduce their dose once they've reached a stable weight. There's no single right approach, and it should be guided by a clinician based on your circumstances. Totiva's pharmacist-led support is available throughout treatment, including for anyone thinking about dose reduction or stopping.

Which medication is right for you?#

If you're currently considering weight loss medication in the UK, the honest answer is that Mounjaro and Wegovy are the only properly evidenced, licensed options available to you right now.

Between those two, Mounjaro consistently produces greater weight loss. If maximum efficacy is the priority and you meet the eligibility criteria, it's the stronger option. Wegovy remains a well-evidenced choice, particularly if you have established cardiovascular disease (where its SELECT trial data is relevant), prefer a tablet formulation, or find Mounjaro's side effects harder to tolerate.

For specific patient profiles:

• Type 2 diabetes with obesity: Both Mounjaro and Wegovy have data here. Mounjaro was originally developed as a diabetes treatment and has strong blood sugar data. Discuss with your prescribing clinician.
• Cardiovascular risk: Wegovy currently has the strongest cardiovascular outcome data from SELECT. Mounjaro's cardiovascular trial (SURPASS-CVOT) also showed benefit.
• GI sensitivity: If you've struggled with nausea on GLP-1 medications before, oral semaglutide (Wegovy tablets) may be worth considering. Dose escalation pace can also be adjusted.
• Budget: Wegovy's lower doses start cheaper, but Mounjaro's superior weight loss may mean you achieve your goal faster. Total cost of treatment isn't just about price per pen.

Retatrutide and CagriSema are worth watching. The clinical data is genuinely exciting. But they're not available in the UK right now, and speculating about timelines is just that: speculation.

A note on unlicensed sources#

With all the interest in newer medications, it's worth being direct: some online sources are offering compounded or grey-market GLP-1 medications, including versions of retatrutide sourced outside the regulated supply chain. The MHRA has taken action on unlicensed compounded GLP-1 medications in the UK. These products carry real risks, including unknown purity, incorrect dosing, and no clinical oversight.

If a website is offering retatrutide as a treatment you can order today, that's a red flag. Stick with medications that are MHRA-licensed and obtained through GPhC-registered pharmacies.

Next steps#

If you're ready to explore what's actually available to you now, a pharmacist-led online consultation is a sensible starting point. Totiva's consultations are free, and you only pay if treatment is found to be suitable for you after a clinician review. There's no subscription, no hidden price increases, and no pressure.

You can start a weight loss consultation with Totiva to find out which treatment fits your circumstances, your health history, and your goals. Whether that's Mounjaro, Wegovy injections, or oral semaglutide tablets, the right choice depends on a proper assessment rather than a comparison table alone.