How to switch from Mounjaro to Wegovy safely

Jump to: Dose conversion guide | Key differences | Cardiovascular benefits and weight loss | Contraception considerations | What to expect | Common myths | How to switch safely | Managing side effects | Frequently asked questions | Take home message

You can switch from Mounjaro (tirzepatide) to Wegovy (semaglutide) safely under medical supervision. Many UK prescribers use a 7-day interval between your last Mounjaro dose and first Wegovy injection, though the exact timing may vary by prescriber or clinic.

Many UK patients are considering this switch following the Mounjaro price increase in September 2025. Beyond cost, Wegovy offers specific advantages worth considering, including a licensed cardiovascular indication and no interaction with oral contraceptives.

While Mounjaro produces slightly greater average weight loss in clinical trials (20-25% vs 15-17%), individual responses vary significantly.^1,2

Some patients may respond better to Wegovy, and with proper support, you can achieve significant weight loss with either medication.

Dose conversion guide: Mounjaro to Wegovy

When switching from Mounjaro to Wegovy, your prescriber may start you at a higher dose than the standard 0.25 mg if they deem it appropriate based on your current dose and tolerance.

The following table reflects one commonly used clinical approach. There are no formally validated dose-equivalence ratios between tirzepatide and semaglutide, so these are possible starting doses your prescriber might consider rather than fixed recommendations:

A note on ‘off-label’ dosing: Wegovy’s licensed starting dose is 0.25 mg. Starting at a higher dose is technically off-label but is commonly used in specialist obesity practice when switching from another GLP-1 medication. Your prescriber will assess your tolerance and determine the safest approach.

If you experienced significant side effects on Mounjaro, your prescriber may recommend starting at a lower Wegovy dose than shown above.

Key differences: Mounjaro vs Wegovy

Understanding the differences between these medications helps you make an informed decision about switching.

Cardiovascular benefits and weight loss comparison

Both medications have demonstrated cardiovascular benefits in clinical trials, though only Wegovy currently holds a UK licence for cardiovascular risk reduction.

The SELECT trial, which included 17,604 participants with established cardiovascular disease, found that semaglutide (Wegovy) reduced the risk of major adverse cardiovascular events (MACE) by 20% compared with placebo.³

MACE includes cardiovascular death, non-fatal heart attack, and non-fatal stroke. Based on these findings, the MHRA approved Wegovy for cardiovascular risk reduction in July 2024.

Tirzepatide (Mounjaro) has also shown cardiovascular benefits. The SURPASS-CVOT trial demonstrated a modest (~10%) reduction in MACE compared with placebo, though this did not reach conventional statistical significance.⁵ Further trials investigating tirzepatide’s cardiovascular outcomes are ongoing.

The most important current difference is regulatory: Wegovy has a licensed cardiovascular indication, whereas tirzepatide’s cardiovascular benefits are still being clarified. This means prescribers can specifically recommend Wegovy for patients with established heart disease, whereas Mounjaro’s cardiovascular benefits, while observed, are not yet part of its licensed indications.

If you have established cardiovascular disease or significant risk factors, discuss with your prescriber whether the licensed cardiovascular indication is an important consideration for your treatment choice.

Real-world weight loss differences

Clinical trials suggest Mounjaro produces greater weight loss than Wegovy (20-25% versus 15-17%).^1,2 However, real-world data suggests the gap may be smaller than trial results indicate.

On Second Nature’s programme, our members lose a similar amount of weight on the two medications. A 12-month retrospective study published in JMIR Formative Research compared outcomes for participants using either tirzepatide or semaglutide within the same behavioural support programme.⁶ The results showed:

• Tirzepatide users lost an average of 22.1% of their starting weight
• Semaglutide users lost an average of 17.1% of their starting weight

While tirzepatide showed greater average weight loss, both medications exceeded the 10% threshold considered clinically significant, with 95.2% of tirzepatide users and 83.1% of semaglutide users achieving this level of weight loss.

It’s worth noting that this was an observational study, not a randomised head-to-head trial, so the comparison has limitations.

However, it suggests that in real-world settings with appropriate lifestyle support, the difference between the medications may be smaller than trial data indicate. Individual responses vary considerably, and some people respond better to one medication than the other.

Contraception considerations when switching

If you use oral contraceptives (the pill), there’s an important difference between these medications you should know about.

Mounjaro and oral contraceptives: Tirzepatide (Mounjaro) can substantially reduce the absorption of oral contraceptive pills (up to around two-thirds in some pharmacokinetic measures), potentially making them less effective.⁴ The manufacturer recommends using barrier contraception (such as condoms) for 4 weeks after starting Mounjaro and after each dose increase.

Wegovy and oral contraceptives: Semaglutide (Wegovy) has no clinically relevant effect on the absorption or effectiveness of oral contraceptives.⁴ No additional precautions are needed.

Non-oral contraceptives: Neither medication affects non-oral contraceptives, including:

• Contraceptive patch
• Vaginal ring
• Hormonal IUD (coil)
• Contraceptive implant
• Contraceptive injection

If you’re currently using the pill while on Mounjaro and want to continue using oral contraception after switching, Wegovy offers the advantage of no interaction concerns.

What to expect when switching

The transition between these medications typically goes smoothly, but there are some changes you may notice.

During the washout period

Some people worry about the gap between stopping Mounjaro and starting Wegovy. In clinical practice, this concern is often overestimated:

• Tirzepatide has a half-life of around 5 days, meaning it remains active in your system for several days after your last injection
• Many people do not notice major appetite changes during a short washout period
• A short washout, such as 7 days, is not usually associated with marked weight regain, especially if lifestyle habits are maintained

First few weeks on Wegovy

Your body needs time to adjust to the different medication. Wegovy works by mimicking one hormone (GLP-1), while Mounjaro mimics two (GLP-1 and GIP).

Appetite changes: You may notice slightly different hunger patterns initially. Some patients report increased hunger during the first 2–3 weeks before the medication reaches full effect. Others notice no difference at all.

Side effects: You may experience different side effects as the medications work through slightly different pathways:

• Nausea and digestive symptoms may temporarily increase or change
• Some patients report less fatigue with Wegovy compared to Mounjaro
• Headaches sometimes occur during the transition, but typically resolve

Weight: Your weight may fluctuate slightly during the transition. This is normal and doesn’t indicate the medication isn’t working. Once you reach your maintenance dose, weight loss typically continues.

Common myths about switching

There’s a lot of misinformation about switching between these medications. Here’s what the evidence actually shows.

Myth: You’ll regain weight when switching

Reality: With a short washout period, significant weight regain is unlikely. Tirzepatide remains active in your system during this time, and Wegovy begins working shortly after your first injection. In clinical practice, most patients maintain their weight throughout the transition, especially when lifestyle habits are maintained.

Myth: You have to start at the lowest Wegovy dose

Reality: While the licensed starting dose is 0.25 mg, prescribers commonly start patients switching from Mounjaro at higher doses based on their current dose and tolerance. This is commonly used in specialist obesity practice and generally safe when supervised by an experienced prescriber, though anything above 0.25 mg is technically off-label.

Myth: Wegovy is ‘weaker’ than Mounjaro

Reality: Wegovy works differently, not weaker. While clinical trial averages favour Mounjaro, individual responses vary significantly. Some patients achieve better outcomes with Wegovy, and many maintain similar weight loss to that observed with Mounjaro.

Myth: You need weeks off between medications

Reality: A commonly used protocol is 7 days between your last Mounjaro dose and first Wegovy injection, though some product information and clinics advise longer gaps (up to 30 days). Your prescriber will balance this against the risk of interrupting treatment. There is no single national standard, and different services use slightly different intervals.

Myth: Once you switch, you can’t go back

Reality: You can switch back to Mounjaro later if needed, under medical supervision. However, you would need to follow a similar protocol, potentially starting at a lower dose of Mounjaro.

How to switch safely from Mounjaro to Wegovy

Switching between these medications should follow a structured approach under medical supervision.

Step 1: Medical assessment

Before switching, your prescriber will evaluate:

• Your current Mounjaro dose and how long you’ve been on it
• Your weight loss progress so far
• Any side effects you’ve experienced
• Your overall health status and any other medications
• Your reasons for wanting to switch

Step 2: Timing the transition

• Take your final Mounjaro injection as scheduled
• Wait for the interval recommended by your prescriber (commonly 7 days, though this may vary)
• Start Wegovy at the dose recommended by your prescriber
• Continue injecting on the same day each week

Step 3: Dose escalation

If you’re starting at a lower Wegovy dose than your maintenance target, you’ll follow this escalation schedule:

• 0.25 mg for 4 weeks
• 0.5 mg for 4 weeks
• 1 mg for 4 weeks
• 1.7 mg for 4 weeks
• 2.4 mg maintenance dose

Your prescriber may adjust this schedule based on your starting dose and how you respond.

Step 4: Follow-up

Schedule a follow-up appointment 2–4 weeks after starting Wegovy to assess how you’re responding and address any concerns.

Managing side effects during the transition

Some people experience temporary side effects when switching between GLP-1 medications. Here are practical strategies to manage the most common issues.

Nausea and digestive discomfort

• Eat three balanced meals a day based on whole foods
• Choose gentle, easy-to-digest foods during the first few weeks, such as scrambled eggs, white fish, and cooked vegetables
• Stay well hydrated between meals (aim for 2 litres daily)
• Limit the intake of ultra-processed foods and takeaways
• Consider ginger tea or supplements, which may help reduce nausea in some people

Fatigue

• Ensure adequate protein intake (at least 25% of each meal)
• Include iron-rich foods like red meat and spinach alongside vitamin C sources
• Maintain consistent sleep habits
• Don’t skip meals, even if your appetite is reduced

Changes in appetite

• Maintain three balanced meals a day based on whole foods, even if hunger is low
• Focus on protein-rich foods at each meal (aim for 30–40g per meal)
• Include plenty of non-starchy vegetables to maximise nutrient density of meals
• Plan healthy snacks for times when hunger might increase

Most transition-related side effects resolve within 2–4 weeks as your body adjusts to the new medication.

Frequently asked questions

Will I regain weight when switching from Mounjaro to Wegovy?

Significant weight regain during the switch is unlikely. A short washout period means tirzepatide’s effects overlap with Wegovy starting to work.

In clinical practice, most patients maintain their weight throughout the transition, especially when lifestyle habits are maintained.

Do I have to start Wegovy at the lowest dose?

Not necessarily. While the licensed starting dose is 0.25 mg, prescribers commonly start patients switching from Mounjaro at higher doses.

Your starting dose depends on your current Mounjaro dose, your tolerance, and your prescriber’s assessment. Starting above 0.25 mg is off-label but commonly used in specialist practice.

Can I switch back to Mounjaro later?

Yes, switching back is possible under medical supervision. You would follow a similar protocol, likely starting at a lower Mounjaro dose and titrating up. However, factors like cost and availability may affect this decision.

Which medication has worse side effects?

Neither medication consistently has worse side effects. Responses are highly individual:

• Some patients report less nausea with Wegovy than Mounjaro
• Others experience fewer digestive issues with Mounjaro
• Both medications can cause similar side effects (nausea, constipation, fatigue)
• The intensity often depends on how quickly doses are escalated

Does Wegovy affect my contraceptive pill?

No. Unlike Mounjaro, Wegovy (semaglutide) has no clinically relevant effect on oral contraceptives.⁴ This is an advantage if you rely on the pill for contraception.

Why do some prescribers use 7 days rather than 30?

While some manufacturer guidance suggests 30 days, many UK prescribers use a 7-day protocol. This shorter gap is based on clinical experience suggesting it’s safe and effective, while avoiding prolonged treatment interruption that could affect weight management.

However, there is no single national standard, and your prescriber will advise based on your individual circumstances.

How long will it take for me to feel normal on Wegovy?

Most patients adjust within 2–4 weeks after starting Wegovy. Any initial side effects or appetite fluctuations typically stabilise during this time. Reaching your maintenance dose takes 4–5 months following the standard escalation schedule.

What if my appetite comes back strongly during the switch?

Some temporary increase in appetite is normal and doesn’t mean the medication won’t work. Continue eating regular, balanced meals with adequate protein.

Once Wegovy reaches therapeutic levels, appetite suppression typically returns. Contact your prescriber if you’re concerned.

Is Wegovy as effective as Mounjaro for weight loss?

Clinical trials show Mounjaro produces higher average weight loss (20–25% vs 15–17%).^1,2 However, individual responses vary significantly.

Real-world observational data from Second Nature’s programme shows a smaller gap, with tirzepatide users losing 22.1% and semaglutide users losing 17.1% of their starting weight at 12 months, though this was not a randomised comparison.⁶ Some patients achieve similar or better results with Wegovy.

How much does Wegovy cost compared to Mounjaro?

Following Eli Lilly’s price increase in September 2025, Wegovy is now more affordable than Mounjaro for most private patients. Typical monthly costs at the time of writing:

• Wegovy: £149–£249 depending on provider and dose
• Mounjaro: £229–£349 depending on provider and dose

Prices are approximate and vary between providers and over time; check current pricing with your chosen pharmacy or clinic. NHS patients typically pay only the standard prescription charge (£9.90 in England) for either medication if they meet eligibility criteria.

Take home message

Switching from Mounjaro to Wegovy is safe and straightforward when done under medical supervision. A short washout period (commonly 7 days, though this varies by prescriber) is usually sufficient to maintain treatment continuity, and most patients transition without significant issues.

While clinical trial data show Mounjaro produces higher average weight loss, real-world evidence suggests the gap may narrow with appropriate lifestyle support.

Many patients maintain similar results after switching, particularly when they continue with healthy eating habits and regular physical activity.

Whatever medication you take, sustainable weight management comes from the habits you build alongside it. The medication supports your efforts; it doesn’t replace them.

References

1. Jastreboff, A.M., et al. (2022). Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine, 387(3), 205-216.
2. Wilding, J.P., et al. (2021). Once-weekly semaglutide in adults with overweight or obesity. New England Journal of Medicine, 384(11), 989-1002.
3. Lincoff, A.M., et al. (2023). Semaglutide and cardiovascular outcomes in obesity without diabetes. New England Journal of Medicine, 389(24), 2221-2232.
4. Electronic Medicines Compendium. (2024). Mounjaro Summary of Product Characteristics.
5. Nicholls, S.J., et al. (2025). Tirzepatide and cardiovascular outcomes in patients with type 2 diabetes. New England Journal of Medicine.
6. Richards, R., et al. (2025). Semaglutide and tirzepatide in a remote weight management program: 12-month retrospective observational study. JMIR Formative Research, 9, e81912.