Ozempic vs Mounjaro Safety: Side Effects Compared | UK

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Pricing Disclaimer: Prices on some pages may not be up to date — the live pricing table below and pricing shown during consultation are official current prices and take precedence over any other figures on the site.

Mounjaro (Tirzepatide)
Weeks 1–4

2.5mg

1 pen • 4 Weeks

£145 £124.99

£31.25 / Per Week

Your starting dose – designed to help your body adjust gently to treatment

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Mounjaro (Tirzepatide)
Weeks 5–8

5mg

1 pen • 4 Weeks

£179 £159.00

£39.75 / Per Week

First step up – builds on your progress as your body adapts to treatment

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Mounjaro (Tirzepatide)
Weeks 9–12

7.5mg

1 pen • 4 Weeks

£220 £200.00

£50.00 / Per Week

Mid-range dose – for continued progression and enhanced results

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Mounjaro (Tirzepatide)
Weeks 13–16

10mg

1 pen • 4 Weeks

£245 £225.00

£56.25 / Per Week

Higher strength dose – supports significant weight loss progress

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Mounjaro (Tirzepatide)
Weeks 17–20

12.5mg

1 pen • 4 Weeks

£270 £250.00

£62.50 / Per Week

Advanced dose – for patients requiring stronger therapeutic effect

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Mounjaro (Tirzepatide)
Weeks 21+

15mg

1 pen • 4 Weeks

£287 £267.00

£66.75 / Per Week

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Wegovy (Semaglutide)
Weeks 1–4

0.25mg

1 pen • 4 Weeks

£89 £69.00

£17.25 / Per Week

Your starting dose – eases your body into treatment with minimal side effects

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Wegovy (Semaglutide)
Weeks 5–8

0.5mg

1 pen • 4 Weeks

£99 £79.00

£19.75 / Per Week

First step up – continues building tolerance for long-term success

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Wegovy (Semaglutide)
Weeks 9–12

1mg

1 pen • 4 Weeks

£119 £99.00

£24.75 / Per Week

Mid-range dose – where most patients start seeing meaningful results

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Wegovy (Semaglutide)
Weeks 13–16

1.7mg

1 pen • 4 Weeks

£169 £149.00

£37.25 / Per Week

Higher strength – supports accelerated weight loss progress

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Wegovy (Semaglutide)
Weeks 17+

2.4mg

1 pen • 4 Weeks

£199 £179.00

£44.75 / Per Week

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Wegovy Oral Pill
Weeks 1–4

1.5mg

1 pen • 4 Weeks

£83.00 £63.00

£20.75 / Per Week

Your starting dose – eases your body into treatment with minimal side effects

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Wegovy Oral Pill
Weeks 5–8

4mg

1 pen • 4 Weeks

£110.00 £90.00

£27.50 / Per Week

First step up – continues building tolerance for long-term success

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Wegovy Oral Pill
Weeks 9–12

9mg

1 pen • 4 Weeks

£140.00 £120.00

£35.00 / Per Week

Mid-range dose – where most patients start seeing meaningful results

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Wegovy Oral Pill
Weeks 13+

25mg

1 pen • 4 Weeks

£199.00 £179.00

£49.75 / Per Week

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Ozempic vs Mounjaro Safety: Side Effects Compared

Published on: June 03, 2026

Understanding ozempic vs mounjaro side effects uk is essential when choosing between these two weight loss treatments. Both medications are GLP-1 receptor agonists licensed by the MHRA, but they differ in mechanism, side effect profiles, and overall tolerability based on extensive clinical trial data.

Understanding Ozempic vs Mounjaro Side Effects UK: Key Differences

Ozempic (semaglutide) and Mounjaro (tirzepatide) share similar gastrointestinal side effects due to their GLP-1 activity, but important differences exist. Mounjaro is a dual GIP/GLP-1 receptor agonist, whilst Ozempic targets only the GLP-1 pathway [1]. This dual mechanism may influence both efficacy and tolerability.

In the SURPASS-2 head-to-head trial comparing tirzepatide directly against semaglutide 1mg, both medications showed comparable rates of nausea (17-22% for tirzepatide vs 18% for semaglutide), but tirzepatide demonstrated slightly higher rates of diarrhoea and vomiting at the highest doses [1]. However, discontinuation rates due to adverse events were similar between treatments, ranging from 4.3% to 7.1% across tirzepatide doses versus 3.6% for semaglutide.

Most side effects with both medications occur during dose escalation and typically diminish over time as the body adapts. UK prescribers carefully titrate doses over several weeks to minimise these effects whilst optimising therapeutic benefit [2].

Common Side Effects: Mounjaro vs Ozempic Safety Comparison

Both tirzepatide and semaglutide primarily affect the gastrointestinal system. The most frequently reported side effects include nausea, diarrhoea, vomiting, constipation, and decreased appetite. These effects are directly related to how GLP-1 receptor agonists slow gastric emptying and influence satiety signals [1][3].

Clinical trial data shows nausea affects approximately 18-22% of patients on either medication, typically peaking during the first 8-12 weeks of treatment. Diarrhoea occurs in 15-20% of patients, whilst vomiting affects 8-12%. With both medications, these effects are generally mild to moderate and resolve without intervention as treatment continues [1][2].

Less common side effects shared by both treatments include injection site reactions (redness, itching, or swelling), fatigue, headache, and dyspepsia. Serious adverse events are rare with both medications but include potential risks of pancreatitis, gallbladder disease, and hypoglycaemia when combined with certain diabetes medications [3].

Managing Gastrointestinal Side Effects

UK clinical experience shows that starting with smaller meals, avoiding high-fat foods, and staying well-hydrated can significantly reduce gastrointestinal discomfort with both medications. Your prescriber may adjust your dose escalation schedule if side effects become problematic, allowing your body more time to adapt before increasing the dose.

Serious Side Effects: Which Is Safer Mounjaro or Ozempic?

Both medications carry similar warnings for serious but rare adverse events. The MHRA requires both Ozempic and Mounjaro to include warnings about potential thyroid C-cell tumours based on rodent studies, though no causal relationship has been established in humans [3]. Both are contraindicated in patients with personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2.

Pancreatitis has been reported with both semaglutide and tirzepatide, occurring in less than 1% of patients in clinical trials. Symptoms include severe abdominal pain radiating to the back, and patients should discontinue treatment immediately if pancreatitis is suspected [1][3]. Gallbladder problems, including cholelithiasis and cholecystitis, have also been observed with both medications, likely related to rapid weight loss rather than the drugs themselves.

Hypoglycaemia risk is low when either medication is used alone, but increases when combined with insulin or sulfonylureas. In the SURPASS-2 trial, severe hypoglycaemia was rare with tirzepatide monotherapy (less than 0.1%), similar to semaglutide [1]. UK prescribers carefully review concurrent medications during assessment to minimise this risk.

Cardiovascular Safety Profile

Semaglutide has demonstrated cardiovascular benefits in the STEP trials, with reductions in major adverse cardiovascular events in high-risk patients [2]. Tirzepatide's cardiovascular outcome data is still emerging, though early signals from the SURPASS trials suggest a favourable safety profile. Both medications have shown improvements in cardiovascular risk factors including blood pressure and lipid profiles [1][4].

Side Effect Mounjaro (Tirzepatide) Ozempic (Semaglutide) Severity
Nausea 17-22% of patients 18% of patients Mild to moderate
Diarrhoea 16-18% of patients 12% of patients Mild to moderate
Vomiting 8-10% of patients 8% of patients Mild to moderate
Constipation 6-8% of patients 5-7% of patients Mild
Injection site reactions 2-4% of patients 2-3% of patients Mild
Discontinuation due to adverse events 4.3-7.1% 3.6% Varies
Pancreatitis <1% of patients <1% of patients Serious
Hypoglycaemia (monotherapy) <0.1% <0.1% Rare

Tirzepatide vs Semaglutide Side Effects: Clinical Trial Data

The SURPASS-2 trial provides the most direct comparison of tirzepatide versus semaglutide safety. In this 40-week study of 1,879 adults with type 2 diabetes, tirzepatide at 5mg, 10mg, and 15mg doses was compared against semaglutide 1mg [1]. Treatment-emergent adverse events occurred in 81-86% of tirzepatide patients versus 81% of semaglutide patients, with most events being mild to moderate.

Gastrointestinal adverse events were the primary reason for discontinuation across all groups. Nausea rates were 17%, 19%, and 22% for tirzepatide 5mg, 10mg, and 15mg respectively, compared to 18% for semaglutide. Diarrhoea was slightly more common with tirzepatide (16-18%) than semaglutide (12%), whilst vomiting ranged from 8-10% across tirzepatide doses versus 8% for semaglutide [1].

The STEP programme trials for semaglutide in obesity showed similar tolerability patterns. In STEP 1, which studied semaglutide 2.4mg for weight management, gastrointestinal disorders were reported in 74% of semaglutide patients versus 48% of placebo patients, with most events being transient and mild to moderate [2]. This higher dose used for weight loss may produce slightly more gastrointestinal effects than the 1mg dose used in diabetes treatment.

Mounjaro Safety Profile UK: What Patients Experience

Real-world UK experience with Mounjaro since its 2023 launch aligns closely with clinical trial data. Most patients tolerate the medication well when dose escalation follows the recommended schedule: starting at 2.5mg weekly for four weeks, then increasing to 5mg, with further increases to 7.5mg, 10mg, 12.5mg, or 15mg based on individual response and tolerability [1].

At Cured Pharmacy, our clinical team finds that patients who experience significant nausea or vomiting often benefit from remaining at their current dose for an additional month before escalating. This personalised approach, combined with dietary modifications and proper injection technique, helps optimise tolerability whilst maintaining therapeutic benefit.

Mounjaro is available at Cured Pharmacy from £124.99, with all doses requiring clinical assessment by a UK prescriber. Our superintendent pharmacist Tarun Kumar (GPhC 2233073) and clinical team provide ongoing support to help patients manage any side effects and achieve their weight management goals safely.

Long-Term Safety Considerations

Both medications have been studied for up to 72 weeks in clinical trials, demonstrating sustained tolerability over extended treatment periods [1][2]. Most gastrointestinal side effects peak during the first 20 weeks and decline thereafter. Long-term safety monitoring continues as these medications are used more widely in clinical practice, with UK prescribers reviewing patients regularly to assess ongoing suitability.

Choosing Between Ozempic and Mounjaro: Safety Factors to Consider

When comparing ozempic mounjaro comparison uk safety profiles, both medications demonstrate similar overall tolerability with comparable discontinuation rates. The choice between them often depends on individual factors including treatment goals, previous medication experience, concurrent health conditions, and cost considerations rather than safety differences alone.

Patients with a history of gastrointestinal conditions may require closer monitoring with either medication. Those taking medications that affect blood sugar should be carefully assessed for hypoglycaemia risk. Both treatments are contraindicated in pregnancy, and women of childbearing potential should use effective contraception [3][4].

Your UK prescriber will consider your complete medical history, current medications, and personal circumstances when recommending the most appropriate treatment. At Cured Pharmacy, our online consultation takes under three minutes and ensures a thorough clinical assessment by UK-registered prescribers before any medication is dispensed. Alternative treatments including Wegovy and Saxenda are also available, each with distinct safety profiles that may suit different patients.

When to Contact Your Prescriber

Seek immediate medical attention if you experience severe abdominal pain that doesn't resolve, persistent vomiting preventing fluid intake, signs of allergic reaction (rash, swelling, difficulty breathing), or symptoms of pancreatitis. Contact your prescriber if side effects are significantly affecting your quality of life or if you have concerns about continuing treatment. Most side effects can be managed through dose adjustments or supportive measures without discontinuing treatment entirely.

Scientific References

  1. Frías, J. P., Davies, M. J., Rosenstock, J., et al. (2021). Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes. New England Journal of Medicine, 385(6), 503–515. https://doi.org/10.1056/NEJMoa2107519 [accessed 13 August 2026]
  2. Wilding, J. P. H., Batterham, R. L., Calanna, S., et al. (2021). Once-Weekly Semaglutide in Adults with Overweight or Obesity. New England Journal of Medicine, 384(11), 989–1002. https://doi.org/10.1056/NEJMoa2032183 [accessed 13 August 2026]
  3. Medicines and Healthcare products Regulatory Agency. (2023). Summary of Product Characteristics: Mounjaro 2.5 mg solution for injection in pre-filled pen. MHRA. https://www.gov.uk/government/organisations/medicines-and-healthcare-products-regulatory-agency [accessed 13 August 2026]
  4. Jastreboff, A. M., Aronne, L. J., Ahmad, N. N., et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine, 387(3), 205–216. https://doi.org/10.1056/NEJMoa2206038 [accessed 13 August 2026]
  5. NHS. (2026). Tirzepatide: a medicine to manage type 2 diabetes and treat obesity. https://www.nhs.uk/medicines/tirzepatide/ Accessed 13 August 2026.
  6. NHS. (2026). Overweight and obesity in adults. https://www.nhs.uk/conditions/overweight-and-obesity/ Accessed 13 August 2026.
  7. NHS England. (2026). Weight management injections. https://www.england.nhs.uk/ourwork/prevention/obesity/medicines-for-obesity/weight-management-injections/ Accessed 13 August 2026.

Information on this page is for educational purposes only and is not medical advice. All prescription treatments require clinical assessment by a UK-registered prescriber. Always consult a qualified healthcare professional before starting any new medication.

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Faq

Which has worse side effects, Ozempic or Mounjaro?
Clinical trials show similar overall side effect profiles, with both medications causing primarily gastrointestinal effects like nausea and diarrhoea in 15-22% of patients. Discontinuation rates due to side effects are comparable at 3.6-7.1%.
Do Mounjaro side effects go away over time?
Yes, most gastrointestinal side effects peak during the first 8-12 weeks of treatment and typically diminish as your body adapts. Clinical trials show reduced side effect rates after the initial dose escalation period.
Is Mounjaro safer than Ozempic for weight loss?
Both medications have similar safety profiles based on clinical trial data, with comparable rates of adverse events and discontinuation. The choice between them should be based on individual factors assessed by your UK prescriber rather than safety differences alone.
What are the most serious side effects of Mounjaro and Ozempic?
Both medications carry rare but serious risks including pancreatitis, gallbladder disease, and potential thyroid tumours (based on animal studies). Severe hypoglycaemia can occur when combined with certain diabetes medications. Both require MHRA-mandated warnings for these conditions.
Can I switch from Ozempic to Mounjaro if I have side effects?
Switching between medications is possible under prescriber guidance, though both share similar gastrointestinal side effects due to their GLP-1 activity. Your UK prescriber can assess whether switching is appropriate or if dose adjustment might better address your concerns.
How long do Mounjaro side effects last after stopping?
Tirzepatide has a half-life of approximately 5 days, meaning it takes about 4-5 weeks to fully clear from your system after stopping. Most side effects resolve within 1-2 weeks of discontinuation as medication levels decline.
Are Mounjaro side effects dose-dependent?
Yes, clinical trials show higher doses of tirzepatide (10mg, 12.5mg, 15mg) produce slightly more gastrointestinal side effects than lower doses (2.5mg, 5mg). This is why UK prescribers use gradual dose escalation to improve tolerability.
Which causes more nausea, Mounjaro or Ozempic?
Head-to-head trials show very similar nausea rates: 17-22% for Mounjaro versus 18% for Ozempic at comparable doses. Individual response varies, and nausea typically improves after the first few weeks of treatment.
Which has worse side effects - Ozempic or Mounjaro?
Both Ozempic and Mounjaro share similar gastrointestinal side effects like nausea and diarrhoea, though Mounjaro may cause slightly more frequent nausea initially due to its dual-action mechanism. Most side effects for both medications are mild to moderate and typically reduce after the first few weeks. Cured Pharmacy provides full prescriber support to help manage any side effects you experience.
Do Ozempic and Mounjaro side effects differ by dose strength?
Yes, side effects for both Ozempic and Mounjaro tend to increase with higher doses, which is why both medications use a gradual dose escalation schedule. Starting at lower doses like Mounjaro 2.5mg or Ozempic 0.25mg helps your body adjust and minimises side effects. Cured Pharmacy's prescribers carefully titrate your dose to balance effectiveness with tolerability.
Can I switch from Ozempic to Mounjaro if I experience side effects?
Yes, switching between Ozempic and Mounjaro is possible under prescriber guidance, and some patients find they tolerate one better than the other despite similar side effect profiles. Your prescriber will assess your specific side effects and medical history before recommending a switch. Cured Pharmacy offers consultations to help determine whether switching medications is right for you.
Are Mounjaro side effects more severe than Ozempic in the UK?
Clinical trials show Mounjaro and Ozempic have comparable side effect severity, with nausea, vomiting, and diarrhoea being the most common for both medications. Mounjaro's dual GIP/GLP-1 action may produce slightly different individual responses, but neither is universally more severe. Cured Pharmacy's UK-registered prescribers monitor your progress and adjust treatment to minimise any adverse effects.
How long do Ozempic vs Mounjaro side effects typically last?
Most side effects from both Ozempic and Mounjaro are strongest during the first 4-8 weeks and gradually decrease as your body adapts to the medication. Gastrointestinal symptoms like nausea typically improve significantly after each dose increase stabilises. Cured Pharmacy provides ongoing support throughout your treatment to help you manage side effects effectively during the adjustment period.
Tarun Kumar, Prescribing Pharmacist

Medically reviewed by

Tarun Kumar, Prescribing Pharmacist (GPhC 2233073)

Reviewed on: June 03, 2026

Last reviewed: 13 August 2026

Last updated on 13 August 2026.

Review History

Our experts continually monitor new findings in health and medicine, and we update our articles when new information becomes available.

Why this page was updated on 13 August 2026

Content checked and updated as part of our periodic review, to ensure accuracy and currentness.

Current version (13 August 2026)

Edited by: The Editorial Team

Medically reviewed by:

Tarun Kumar, GPhC No. 2233073, Prescribing Pharmacist


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