Can I Switch From Wegovy to Mounjaro Straight Away? (October 2026)

01 · The verdict

Can you switch from Wegovy to Mounjaro straight away?

No, not as an automatic same-day swap. There is no licensed direct conversion between semaglutide (Wegovy) and tirzepatide (Mounjaro), so the switch is done under prescriber supervision.¹ Typically the previous medicine is stopped, a washout interval is observed, and Mounjaro starts at a dose your prescriber judges appropriate. That is often the 2.5mg starting dose, sometimes adjusted based on your history.

You may see a single fixed number of days quoted online as the gap. No licensed rule sets one. The interval is a clinical judgement that depends on your dose, your last injection date and how you have tolerated treatment. The one firm rule is that the two medicines are never taken together.

The question is also asked in reverse: can you switch from Mounjaro to Wegovy straight away? The same principle applies: your prescriber decides when to switch and which Wegovy dose to start on. There is a dedicated guide on how long to wait when moving to Wegovy.

02 · Comparison

Wegovy and Mounjaro compared

Both are effective, licensed weight-management treatments. Which suits you depends on your health profile, tolerance and prescriber advice, not the headline number alone.¹⁵

See the Wegovy pen and Mounjaro pen pages for current prices and availability.

03 · Deciding

What to weigh before you switch

The reason for switching matters more than the speed of the switch. People usually move for one of three reasons: results have plateaued, side effects are hard to tolerate, or cost and supply have changed.

Be realistic about each. Mounjaro averaged more weight loss than Wegovy in SURMOUNT-5, but trial averages do not predict your own result. A prescriber will also consider your current dose, how long you have been on Wegovy and any other medicines you take. Moving to a different drug does not remove the need for a reduced-calorie diet and more physical activity.²

If you are unsure whether to switch at all, start your free consultation. A GPhC-registered prescriber will review your history and tell you whether switching is suitable.

04 · Washout and overlap

What is the washout period between Wegovy and Mounjaro?

A washout is the planned gap between your last dose of one medicine and your first dose of the next. The aim is to avoid two GLP-1 medicines acting at the same time. The previous medicine is stopped, a washout interval is observed, and Mounjaro then starts at a dose your prescriber judges appropriate.¹

No fixed number of days is licensed. Your prescriber works out the interval from your own dosing history.

Overlap is the real risk. Mounjaro must not be combined with other GLP-1 medicines, and the same applies to Wegovy.¹ Do not inject your next Wegovy dose "just in case" and then start Mounjaro days later. Tell your prescriber exactly when you last injected, and do not guess.

05 · Starting dose after Wegovy

Which Mounjaro dose do you start on after Wegovy?

Most people restart at 2.5mg, because there is no licensed conversion between the two drugs. The dose is your prescriber's call and is sometimes adjusted based on your history.¹ A high Wegovy dose does not translate into an equivalent Mounjaro dose.

That surprises some people who have reached Wegovy 2.4mg and expect to start higher. Starting low is a deliberate safety step, not a setback.

If you are wondering whether you can skip ahead, read our guide on starting at 5mg Mounjaro. Any decision to start above 2.5mg belongs to your prescriber, not to you.

A new customer saves £40 on their first order at any dose with code FIRST40, and an automatic £25 reorder discount applies to every future order (code DOSE25).

06 · What to expect when switching

What to expect in the first weeks on Mounjaro

Expect a new start rather than a continuation. Being on Wegovy does not mean your body is already adjusted to tirzepatide, and side effects can return as you begin a different medicine. Our guide to side effects when switching from Wegovy covers what to watch for.

For context, in the STEP 1 trial gastrointestinal side effects were reported by 74.2% of people on semaglutide 2.4mg, compared with 47.9% on placebo. 7.0% stopped treatment because of side effects, compared with 3.1% on placebo.⁹ Side effects are common with this medicine class.

Wondering when you will feel a difference? See whether Mounjaro works straight away, and our week-by-week guide to changing from Wegovy for a timeline. Report any new or worrying symptom to your prescriber, and you can report side effects through the Yellow Card scheme.¹⁹

07 · Switching the other way

Can you switch from Mounjaro to Wegovy straight away?

No, the same supervised approach applies in reverse, and tirzepatide stays in your system for a while. It has a half-life of about five days, so after a final dose it takes roughly 4–5 weeks to clear. There is no way to speed this up, and nothing needs doing while it clears.¹

Your prescriber decides which Wegovy dose to start on. The licensed ladder runs 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg, stepping up after at least 4 weeks to reach the 2.4mg maintenance dose from week 17.¹⁸

The exact timing is for your prescriber to set. Our guide to moving from Mounjaro to Wegovy explains the process in more detail.

08 · Stopping Wegovy and weight regain

Why do people stop Wegovy, and what about weight regain?

People stop Wegovy for different reasons, including side effects, a plateau, cost or a change of treatment. In STEP 1, 7.0% of people on semaglutide 2.4mg stopped because of side effects.⁹

A gap in treatment is not a pause button for your weight. Mounjaro manages weight; it does not cure the biology behind it. In SURMOUNT-4, people who stopped tirzepatide after 36 weeks regained on average 14% of body weight over the following year, while those who continued treatment lost a further 5.5% on average. Stopping should always be planned with your prescriber, with diet and activity habits ready to carry the load.¹⁴

This is another reason not to leave a long unplanned gap while you decide. If you plan to switch, talk to a prescriber before your next scheduled Wegovy dose so the transition is planned, not improvised.

For the trial results behind both medicines: in STEP 1, adults on Wegovy 2.4mg lost on average 14.9% of body weight over 68 weeks versus 2.4% on placebo. In SURMOUNT-1, people on tirzepatide lost on average 15% on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, versus 3.1% with lifestyle changes alone. These come from different trials and are not a head-to-head comparison.⁹²

09 · Safe supply and shortcuts

Avoiding shortcuts when you switch

Anything that promises a faster or easier switch outside a licensed pathway is a warning sign. Mounjaro must not be combined with other GLP-1 medicines, unlicensed "research" peptides such as retatrutide (which has no UK licence) or compounded copies. These combinations have no safety data and no regulated supply chain.¹

Mounjaro is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber. Be wary of any seller offering to supply without a consultation or prescription. Our Mounjaro comes through official LillyDirect supply, direct from Eli Lilly's UK distribution, as genuine KwikPens.

The same goes for appetite: if you are curious how quickly it kicks in, see whether Mounjaro suppresses appetite straight away.

10 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹

11 · NHS and private routes

NHS or private: how do you switch?

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the primary-care rollout began in June 2025 with the highest-need groups first, initially BMI 40+ with four or more qualifying conditions.⁴⁶ Full rollout is expected to take years, so many people who meet the licensed criteria choose regulated private treatment.

If you are on Wegovy through a specialist weight-management service, speak to that team before changing anything. NHS access to Wegovy runs through specialist weight-management services, so ask your GP.

How ordering works with us

• Complete a free online consultation, a short health questionnaire with no charge or obligation.
• A GPhC-registered prescriber reviews it. Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full.
• We dispense and dispatch, with same-day dispatch when ordered by 3pm, and free next-day tracked delivery in temperature-controlled packaging.

Mounjaro doses are in stock across all six strengths from 2.5mg to 15mg. Ongoing monthly reviews are included, and repeat orders re-check suitability. See all weight loss treatments if you would like to compare other options.