Wegovy vs Mounjaro: Which weight-loss injection is right for you?

Jump to: What are Wegovy and Mounjaro? | How these medications work | Clinical trials vs real-world results | Side effect comparison | Cost and access in the UK | Who might prefer each option? | Frequently asked questions | Take home message

In clinical trials, Mounjaro (tirzepatide) produces greater average weight loss than Wegovy (semaglutide), with the SURMOUNT-5 trial showing 20.2% average weight loss with Mounjaro compared to 13.7% with Wegovy after 72 weeks.

However, Second Nature’s published research shows that people using Wegovy with our comprehensive programme achieve significantly better results than clinical trials, averaging 19.1% weight loss at 12 months compared to the 13.7% seen in trials.

While these results are promising, they come from real-world observational data, which differ from randomised controlled trials in population characteristics and study design.

Nevertheless, they demonstrate the potential for improved weight loss results with Wegovy and other GLP-1 medications when they’re combined with healthy habits.

For someone weighing 100kg, this means you could lose 20.2kg with Mounjaro or up to 19.1kg with Wegovy when combined with Second Nature’s support programme, a much smaller difference than clinical trials suggest.

It’s important to note that individual responses vary widely; some people lose significantly more than average with Wegovy, while others may respond better to Mounjaro.

Both medications are fully approved in the UK for treating obesity, with Wegovy having a longer safety track record as it was approved earlier.

Comparison Point	Wegovy (Semaglutide)	Mounjaro (Tirzepatide)
Average weight loss in trials	13.7%	20.2%
Real-world results with Second Nature	19.1%	Early data collection is ongoing
UK approval date	September 2022	November 2023
Mechanism	GLP-1 receptor agonist	Dual GLP-1/GIP receptor agonist
Side effect discontinuation rate	~4%	6-8.5%
Weekly injection dosing	Typically a fixed progression to 2.4mg, although more flexible dosing is now more widely available	More flexible with three maintenance options (5mg, 10mg, 15mg)
NHS availability	Limited specialist services	Very limited specialist services

What are Wegovy and Mounjaro?

Wegovy and Mounjaro are weekly injectable medications that help control appetite and support weight loss by mimicking hormones that are released by the body after we eat.

Both medications are approved by the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) for treating:

• Obesity (BMI ≥30) or
• Overweight (BMI ≥27) with at least one weight-related health condition

Wegovy, manufactured by Novo Nordisk, contains the drug semaglutide. It received UK approval in September 2022 and has a substantial safety record with millions of users worldwide.

Mounjaro, manufactured by Eli Lilly, contains tirzepatide. It received UK approval in November 2023 for weight management after initially being approved for type 2 diabetes.

How these medications work

Both medications work by mimicking naturally occurring hormones in our body that regulate hunger and blood sugar, but with some important differences:

How Wegovy works

Wegovy mimics one hormone called GLP-1 (glucagon-like peptide-1), which has three key effects:

• Slows food movement through your stomach, helping you feel fuller longer
• Communicates with your brain’s appetite control centre (the hypothalamus) to reduce hunger
• Improves blood sugar control by improving insulin function

The natural GLP-1 hormone in our body lasts only minutes in the blood before it’s removed from the body, while Wegovy’s effects last for days, providing a longer-lasting effect of lowering hunger and cravings.

Many people report that Wegovy not only reduces physical hunger but also diminishes food cravings and “food noise”, the constant thoughts about food that can lead to overeating.

Many patients find that Wegovy’s focused action on the GLP-1 receptor provides effective hunger control with potentially fewer side effects than dual-action medications.

Mounjaro’s dual-action approach

Mounjaro works on two hormone systems instead of one:

• Like Wegovy, it activates the GLP-1 receptor
• It also activates a second receptor called GIP (glucose-dependent insulinotropic polypeptide)

This dual-action approach is likely why Mounjaro supports more weight loss in clinical trials, as it provides additional blood sugar control and hunger management.

Clinical trials vs real-world results

What the clinical trials show

The landmark SURMOUNT-5 trial published in May 2025 directly compared these medications and found:

• Mounjaro (tirzepatide) produced 20.2% average weight loss
• Wegovy (semaglutide) produced 13.7% average weight loss
• The 6.5% difference was statistically significant

This trial used the maximum doses of both medications (Mounjaro 15mg, Wegovy 2.4mg) and lasted 72 weeks, providing the most definitive head-to-head comparison to date.

Real-world results with Second Nature

While clinical trials are the gold standard for comparing medications, they don’t always reflect real-world outcomes, particularly when comprehensive support is provided alongside medication.

Second Nature’s peer-reviewed research published in JMIR Formative Research (2025) found that our programme significantly enhances Wegovy’s effectiveness:

• Participants achieved 19.1% average weight loss at 12 months
• 77% of participants achieved at least 10% weight loss
• 61% of participants achieved at least 15% weight loss
• Side effect management improved with coaching support with 70% of participants reporting no side effects after 12 months

These results demonstrate that while Mounjaro may show greater average weight loss in clinical trials, Wegovy, combined with proper support, can achieve results that approach Mounjaro’s effectiveness for many people.

Side effect comparison

Both medications have similar side effect profiles, primarily affecting the digestive system:

Side Effect	Wegovy (Semaglutide)	Mounjaro (Tirzepatide)
Nausea	Common (40-45%)	Common (40-45%)
Diarrhoea	Common (25-30%)	Common (25-30%)
Vomiting	Less common (20-25%)	Less common (20-25%)
Constipation	Common (20-25%)	Common (25-30%)
Discontinuation rate due to side effects	~4%	6-8.5%

The SURMOUNT-5 trial found that side effects were generally mild to moderate and occurred primarily during dose escalation for both medications.

Important distinction: While side effect profiles are similar, Wegovy has a slightly lower discontinuation rate in clinical trials, suggesting it may be marginally better tolerated by some individuals.

Second Nature’s health coaches provide specialised guidance for managing these side effects, which can significantly improve your medication experience:

• Personalised dietary advice to support health and reduce side effects
• Hydration and meal timing strategies
• Practical approaches for managing nausea and other common side effects

NHS availability

Both medications are theoretically available through NHS specialist weight management services (Tier 3 and Tier 4), but access remains highly limited:

• Eligibility typically requires BMI ≥35 or ≥40 alongside obesity-related comorbidities
• Previous documented attempts at weight loss
• Referral from GP to specialist services
• Significant regional variation in availability

Given these limitations, many eligible patients opt for private treatment while NHS services continue to expand capacity.

Who might prefer each option?

While individual responses vary significantly, certain factors might make one medication more suitable for your specific situation:

Wegovy might be preferred if:

• Cost is a significant consideration – Wegovy is typically £30-100 less per month
• You value a longer safety track record – Wegovy has been approved longer
• You’ve had positive experiences with other GLP-1 medications like Saxenda
• Side effect concerns are primary – Slightly lower discontinuation rate in trials

Mounjaro might be preferred if:

• Maximum average weight loss is the priority – Clinical trials show greater average results
• You have type 2 diabetes alongside obesity – Particularly strong benefits for blood sugar
• You’ve tried Wegovy without achieving the desired results
• You’re comfortable with a newer medication with a growing but shorter safety record

Frequently asked questions

Which is more effective, Wegovy or Mounjaro?

In direct clinical comparison, Mounjaro shows greater average weight loss (20.2% vs 13.7% over 72 weeks).

However, Second Nature’s research demonstrates that with proper support, Wegovy can achieve enhanced results (19.1% at 12 months) that narrow this gap considerably.

Individual responses vary significantly, and some people respond better to Wegovy and vice versa.

Why do people switch between Wegovy and Mounjaro?

People typically switch from Wegovy to Mounjaro seeking greater weight loss if they’ve plateaued, or from Mounjaro to Wegovy due to side effect concerns or cost considerations.

Each medication affects individuals differently, and finding the right match often requires personalised guidance from healthcare providers.

Is Wegovy or Mounjaro cheaper in the UK?

Wegovy is generally more affordable in the UK, given the recent announcement of Mounjaro’s price increase.

Both medications may be available through NHS specialist services for eligible patients, though access remains limited.

How long do you stay on these medications for weight loss?

Current guidelines suggest that these medications are most effective when used long-term, with UK guidance generally recommending at least 12 months of treatment.

NICE guidance recognises obesity as a chronic condition, suggesting that long-term pharmacotherapy may be appropriate for many patients if safe and well-tolerated.

Many patients continue treatment for 2+ years while developing sustainable habits. Second Nature’s approach focuses on building lasting lifestyle changes alongside medication to support long-term success.

Will I gain weight back after stopping these medications?

Some weight regain is common after stopping either medication if sustainable habits haven’t been established.

Second Nature’s published research shows that patients who develop healthy habits alongside medication maintain significantly more weight loss after stopping.

Our programme focuses on building these sustainable changes from day one.

Take home message

Clinical trials show that Mounjaro leads to greater average weight loss than Wegovy (20.2% vs 13.7%), but Second Nature’s research demonstrates that comprehensive support can significantly enhance Wegovy’s effectiveness (19.1% weight loss at 12 months).

Both medications are effective tools for weight management when combined with proper support, and individual responses vary considerably.

The ‘best’ medication depends on your personal health profile, cost considerations, side effect tolerance, and individual response.

What truly matters for long-term success is not just which medication you choose, but the support system and habit changes you develop alongside it.

Second Nature’s approach focuses on building sustainable lifestyle changes that enhance medication effectiveness and help maintain results long-term.