Switching from Mounjaro to Wegovy: A practical guide for UK patients

DoktorABC editorial team

Accurate, up-to-date health information written by our editorial team and reviewed by UK-registered prescribers.

Why might someone switch from Mounjaro to Wegovy?

The most common reasons UK patients are currently considering this switch fall into three broad categories.

Cost

Eli Lilly increased Mounjaro's UK wholesale price by up to 170% from 1 September 2025, aligning UK pricing with other developed markets. For patients on higher maintenance doses (10 mg to 15 mg), monthly costs more than doubled. Wegovy is now typically £60 to £100 per month cheaper at standard maintenance doses, representing a saving of approximately £600 to £1,100 over a full year. For many patients, this is a significant and practical reason to consider switching.

Efficacy at maximum doses

Following the MHRA's approval of Wegovy 7.2 mg on 6 January 2026, the efficacy gap between the two treatments has narrowed considerably. The STEP UP trial showed average weight loss of 20.7% over 72 weeks at the 7.2 mg dose, broadly comparable to Mounjaro's 20.9% at 15 mg in the SURMOUNT-1 trial (New England Journal of Medicine, 2022). For patients who have plateaued on Mounjaro and are considering their options, Wegovy at the higher dose now represents a clinically comparable alternative.

Side effect profile

A small number of patients find Mounjaro's gastrointestinal side effects more pronounced than they would prefer, particularly burping and nausea. Because Wegovy activates only GLP-1 receptors rather than the dual GLP-1 and GIP mechanism of Mounjaro, some patients report a different tolerability profile on semaglutide. This is anecdotal and not consistently supported by direct trial comparisons, but it is a clinically legitimate reason to discuss a switch with your prescriber.

Contraception considerations

Mounjaro can reduce the effectiveness of the contraceptive pill in women who are overweight. The MHRA recommended in June 2025 that these patients use an additional non-oral form of contraception alongside the pill, and for four weeks after each dose increase. Wegovy does not have this interaction with the contraceptive pill, which makes it a simpler option for women who rely on oral contraception. 

Is switching from Mounjaro to Wegovy safe?

Yes, switching from Mounjaro to Wegovy is safe under medical supervision. The two medicines contain different active ingredients and work through different mechanisms, but there is no known harmful interaction between them, and there is no evidence of harm from switching between GLP-1 class medicines.

Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are MHRA-licensed prescription medicines. Both carry the Black Triangle symbol (▼), meaning the MHRA actively encourages reporting of suspected side effects via the Yellow Card scheme at yellowcard.mhra.gov.uk. Switching between them requires a clinical assessment by a UK-registered prescriber, who will review your treatment history, current dose, tolerability, and health profile before issuing a new prescription.

How do you switch from Mounjaro to Wegovy?

The washout period

Most UK prescribers recommend a washout period of seven days between your last Mounjaro injection and your first Wegovy dose. Both medicines have long half-lives (the time it takes for the body to reduce drug concentration by half), and a one-week gap allows overlapping effects to subside before introducing semaglutide.

Dose conversion guidance

There is no exact milligram-to-milligram equivalence between Mounjaro and Wegovy, as the two medicines contain different active ingredients with different molecular structures and potencies. The conversion is a clinical approximation based on your treatment history and tolerability, not a mathematical formula.

The table below reflects the dose conversion approach used by a number of UK regulated prescribers as a general guide. Your prescriber may advise differently based on your individual circumstances.

This table is a general clinical guide only. Your prescriber will assess your individual history and determine the appropriate starting dose. Requesting a specific dose does not guarantee it will be prescribed.

What should you expect when switching from Mounjaro to Wegovy?

Appetite changes

Most patients who switch at an equivalent dose find that appetite suppression continues without significant interruption, though some report a brief period of increased hunger in the first one to two weeks as the body adjusts to a different active ingredient. This typically stabilises as semaglutide reaches a steady state in the bloodstream, usually within two to four weeks.

Side effects during transition

Because Wegovy and Mounjaro share a similar gastrointestinal side effect profile, most patients do not experience a dramatic change in tolerability. Some patients report that gastrointestinal side effects such as burping and nausea are less pronounced on Wegovy, particularly at equivalent dose stages. Others notice little difference. Starting at a lower dose than the Mounjaro equivalent is one approach to managing this transition period if tolerability is a concern.

Weight loss trajectory

Patients who switch at an equivalent dose and maintain their dietary and lifestyle habits generally find that weight loss continues, though the rate may slow temporarily during the transition period. This is not a cause for concern and typically resolves within four to eight weeks as the new medicine reaches stable blood levels.

Switching from Mounjaro to Wegovy: What patients commonly report

It would not be appropriate to reproduce individual testimonials here, but aggregated experience patterns from regulated UK clinical services and patient community forums reflect several consistent themes.

Patients who switch primarily for cost reasons and maintain their lifestyle habits generally report that weight loss continues at a comparable pace, particularly those who switch to the 2.4 mg or 7.2 mg Wegovy dose from Mounjaro's higher maintenance doses. The convenience of a once-weekly injection schedule remains unchanged.

Patients who switch after experiencing pronounced gastrointestinal side effects on Mounjaro (particularly burping and reflux) generally report an improvement in tolerability on Wegovy. This is consistent with clinical trial data showing that these specific side effects are reported slightly more frequently with tirzepatide than with semaglutide.

A smaller number of patients report that appetite suppression feels less strong in the early weeks after switching, particularly those coming from the 12.5 mg or 15 mg Mounjaro dose. This typically improves as the dose increases and as the body adapts to semaglutide.

How do you switch from Wegovy to Mounjaro?

Switching in the reverse direction, from Wegovy to Mounjaro, follows the same principles: a seven-day washout period, a clinical assessment, and a prescriber-determined starting dose based on your treatment history.

The most common reasons for switching from Wegovy to Mounjaro are a desire for greater average weight loss (Mounjaro produces higher average outcomes at standard doses in direct comparisons), a diagnosis of type 2 diabetes where Mounjaro's dual mechanism offers additional metabolic benefits, or a prescriber recommendation based on treatment progress.

This table is a general clinical guide only. Your prescriber will assess your individual history and determine the appropriate starting dose.

What are the most common reasons for changing from Mounjaro to Wegovy?

To summarise the key drivers discussed in this article:

• Cost: The most common reason following the September 2025 Mounjaro price increase. Wegovy is now meaningfully cheaper at most dose stages.
• Comparable efficacy at higher doses: The Wegovy 7.2 mg dose, approved by the MHRA in January 2026, produces average weight loss broadly comparable to Mounjaro 15 mg.
• Tolerability: Some patients find Wegovy's side effect profile more manageable, particularly in relation to burping and reflux.
• Contraception: Wegovy does not carry the same oral contraceptive interaction as Mounjaro, making it a more practical option for some women.
• NHS pathway: Wegovy has an established NICE-approved NHS pathway (TA875) that Mounjaro's NHS access (TA1026, from June 2025) is still catching up with in terms of regional availability.

When should you not switch without direct medical advice?

While switching between these medicines is generally safe under supervision, there are specific circumstances in which you should seek direct clinical guidance before proceeding rather than initiating a switch independently.

• You have a history of pancreatitis, gallbladder disease, or inflammatory bowel disease
• You are pregnant, breastfeeding, or planning a pregnancy
• You have recently experienced significant gastrointestinal complications on either medicine
• You have type 2 diabetes and your blood sugar control may be affected by the switch
• You are taking other medications that interact with either treatment
• You have not yet discussed the switch with a UK-registered prescriber

Final thoughts

Switching from Mounjaro to Wegovy is a clinically straightforward process for most patients when done under proper medical supervision. The dose conversion guidance in this article provides a useful starting framework, but the appropriate starting dose for you will always depend on your individual treatment history and your prescriber's clinical assessment.

The most important step is not finding the right conversion table; it is having the right clinical conversation. If cost, tolerability, or efficacy are driving your thinking, discuss these openly with your prescriber. They can advise on whether switching is appropriate, what dose to start at, and what to expect during the transition.

FAQ

The DoktorABC medical advisory board

Dr. Roland Ruiken

Medical advisor, Norway

Dr. Viktor Simunovic

Medical advisor, Croatia

To the medical advisory board