Mounjaro vs Saxenda: Weekly vs Daily Weight Loss Injections

Introduction – Two GLP-1 Options for Weight Loss

Saxenda (liraglutide 3mg) and Mounjaro (tirzepatide) both belong to the GLP-1 receptor agonist family of medications—drugs that mimic gut hormones to suppress appetite and aid weight loss. But they represent different generations of this technology, with distinct advantages and trade-offs.

Saxenda has been available in the UK since 2015, giving it nearly a decade of real-world use and safety data. It was groundbreaking at the time, offering 5-10% average weight loss when diet and exercise alone often failed.

Mounjaro arrived in 2022 with a novel dual-action mechanism and dramatically superior results—doubling or even tripling Saxenda's weight loss in trials. However, it's newer, with less long-term data, and comes at a slightly higher cost.

This comparison will help you understand which might be right for you, covering effectiveness, convenience, side effects, and access in the UK.

Mechanisms and Dosing: Daily vs Weekly

How Saxenda Works

Saxenda mimics GLP-1, a hormone your gut naturally releases after eating. It:

• Reduces appetite by acting on hunger centres in the brain
• Slows how quickly your stomach empties, keeping you fuller longer
• Helps regulate blood sugar by improving insulin release

Dosing schedule: You inject Saxenda subcutaneously (under the skin) every single day, typically at the same time. You start at 0.6mg and gradually increase over 5 weeks to the full 3mg dose. The pen is multi-dose, lasting about 6 days before you need a new one.

How Mounjaro Works

Mounjaro activates both GLP-1 and GIP receptors:

• All the same GLP-1 benefits as Saxenda (appetite suppression, slower digestion, better insulin function)
• Plus GIP activation: Enhances insulin sensitivity, may improve fat metabolism, and works synergistically with GLP-1 for greater effect

Dosing schedule: Once weekly injection. You start at 2.5mg and increase monthly (if tolerated) up to 5mg, 7.5mg, 10mg, 12.5mg, or the maximum 15mg dose. Each pen is single-use.

Efficacy – How Much Weight Can You Lose?

This is where Mounjaro pulls significantly ahead:

Clinical Trial Results

Saxenda (SCALE trials):

• Average weight loss: 5-8% of body weight over 56 weeks
• About 63% of participants lost ≥5% of their weight
• About 33% lost ≥10%
• For a 100kg person: typical loss of 5-8kg (0.8-1.3 stone)

Mounjaro (SURMOUNT trials):

• Average weight loss: 15-22.5% depending on dose (72 weeks)
• 89% of participants on 15mg lost ≥5%
• 57% lost ≥20%
• For a 100kg person: typical loss of 15-22.5kg (2.4-3.5 stone)

Side Effects Comparison

Both medications cause similar gastrointestinal side effects, as they both work on the GLP-1 system:

Side Effect	Mounjaro	Saxenda
Nausea	20-30%	40-50%
Diarrhoea	12-18%	20-25%
Constipation	10-15%	20-25%
Vomiting	8-12%	15-18%
Injection site reactions	Rare	Slightly more common (daily injections)
Headache	Moderate	Moderate-common

Notable Differences

• Saxenda tends to cause higher rates of GI side effects, particularly nausea and constipation—possibly because it's dosed daily, giving less "break" between doses
• Daily dosing with Saxenda might mean more consistent mild nausea, whereas Mounjaro's weekly dosing might cause periodic stronger nausea for 1-2 days post-injection
• Injection site issues (redness, bruising) are slightly more common with Saxenda simply due to injecting 7x more often
• Both improve over time as your body adjusts, typically within 4-8 weeks

Cost and Accessibility

NHS Access

Saxenda:

• Can be prescribed on the NHS for obesity (BMI ≥35 with comorbidity or ≥40)
• Availability varies by region—some ICBs restrict it heavily due to cost
• Often requires specialist referral to tier 3 weight management service
• Not as widely available as it once was, with NHS shifting focus to newer, more effective options

Mounjaro:

• NICE-approved for NHS obesity use (December 2025), with phased rollout starting
• Similar eligibility: BMI ≥35 with comorbidity or ≥40
• Prioritised over Saxenda in many areas due to superior efficacy
• Limited availability initially, expanding through 2025

Private Costs

Treatment Phase	Mounjaro (Monthly)	Saxenda (Monthly)
Starting dose	£170-£210	£160-£200
Maintenance dose	£250-£350	£180-£230
12-month cost	£2,800-£3,600	£2,000-£2,600

Cost comparison: Saxenda is roughly £600-1,000 cheaper per year privately. However, given Mounjaro delivers 2-4x the weight loss, many consider it better value for money—you're paying slightly more for dramatically better results.

Who Might Choose Which?

Switching from Saxenda to Mounjaro

Many people have successfully transitioned from Saxenda to Mounjaro seeking better results. If you've been on Saxenda and are considering switching:

• Discuss with your prescribing doctor—they'll determine an appropriate Mounjaro starting dose (likely higher than 2.5mg if you're already tolerating Saxenda 3mg)
• Expect a transition period where side effects may temporarily increase
• You should see enhanced weight loss within 2-3 months if Mounjaro works well for you

Frequently Asked Questions

The Bottom Line

Saxenda was revolutionary when it launched, offering hope to millions struggling with obesity. It remains a perfectly valid option with a strong safety record and proven effectiveness.

However, Mounjaro represents a clear advancement in weight loss pharmacotherapy. Its dual mechanism delivers superior results—often double or triple Saxenda's weight loss—with the added convenience of weekly rather than daily injections.

For most people starting a weight loss medication today, Mounjaro is the better choice if accessible and affordable. The significantly greater weight loss and improved convenience justify the marginal extra cost for those who can manage it.

That said, Saxenda still has a place: for those who prefer an established medication with longer-term data, who respond well to it, or who find it more accessible via the NHS or affordably through private providers.

Whichever you choose, remember that medication is just one tool. Combining it with healthy eating, regular activity, good sleep, and stress management will maximise your results and help maintain your weight loss long-term.