Byetta vs Mounjaro: What's the Difference? (October 2026)

01 · The short verdict

Which should you choose: Byetta or Mounjaro?

If your goal is weight management, Mounjaro is licensed for it in adults, and it has large published trials. In the UK it is licensed for weight management in adults and for type 2 diabetes.¹ It is a once-weekly injection from a pre-filled multi-dose KwikPen in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹

Byetta (exenatide) is a different active ingredient. If you are already on Byetta, or your doctor has suggested it, your prescriber or pharmacist is the right person to confirm its current status and your options.

02 · Side by side

Byetta vs Mounjaro comparison table

03 · How to decide

The factors that should drive your decision

Start with your diagnosis and goal. Mounjaro is licensed for weight management and for type 2 diabetes.¹ If you are managing diabetes with a clinician, any change belongs in that clinician's hands, not in an online comparison.

Next, think about convenience. A once-weekly pen means one injection a week rather than a daily routine. That is a practical difference many people weigh, though it is not a clinical reason on its own.

Finally, consider cost. A first-order discount of £40 applies to new customers with code FIRST40, and every later order is £25 off the standard price (code DOSE25). The Mounjaro pen prices and consultation page shows live figures for every dose.

04 · How Mounjaro works

How Mounjaro works

Tirzepatide is the first treatment of its kind to activate two natural gut-hormone receptors at once: GIP and GLP-1.¹ Together these help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin.¹

In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹ This dual action is what distinguishes Mounjaro from single-action GLP-1 medicines such as semaglutide.¹

Tirzepatide has a half-life of about five days, so after a final dose it takes roughly 4–5 weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹

If you want to know whether exenatide belongs in the same family, we cover that separately in our guide on whether Byetta is a GLP-1. Our Byetta and weight loss guide goes into the weight angle.

05 · Mounjaro trial results

What the Mounjaro trials show

In the SURMOUNT-1 trial of 2,539 adults, people taking tirzepatide alongside diet and exercise lost on average 15% of their body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks. The comparison group, on lifestyle changes alone, lost 3.1%.²

These are trial averages. Individual results vary, and treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.² Trial averages do not predict your own result.

At 72 weeks, 85% of participants on 5mg, 89% on 10mg and 91% on 15mg had lost at least 5% of their body weight. Half of participants on 10mg and 57% on 15mg lost at least 20% of their body weight.²

As a worked example only: for someone starting at 100 kg, 20.9% is about 21 kg. Your own start weight, dose, diet and activity will all shape your result.

06 · Mounjaro vs semaglutide

Mounjaro against semaglutide: the head-to-head evidence

SURMOUNT-5 was the first large head-to-head trial of tirzepatide and semaglutide for weight loss. In it, adults on tirzepatide lost on average 20.2% of body weight over 72 weeks versus 13.7% on semaglutide 2.4mg (Wegovy).¹⁵ Both are effective, licensed treatments. Which suits you depends on your health profile, tolerance and prescriber advice, not the headline number alone.¹⁵

In SURMOUNT-5, 751 adults took one medicine or the other for 72 weeks. At least 10% of body weight was lost by 81.6% on tirzepatide versus 60.5% on semaglutide, and at least 15% by 64.6% versus 40.1%. At least 20% was lost by 48.4% versus 27.3%, and at least 25% by 31.6% versus 16.1%. Average loss was 22.8 kg versus 15.0 kg.¹⁵

In the separate STEP 1 trial, adults on semaglutide 2.4mg lost on average 14.9% of body weight over 68 weeks, compared with 2.4% on placebo.⁹ That trial had a different design, so its numbers should not be set against SURMOUNT-1 as if they were head to head.

If you are weighing the two injectables, our guides to Wegovy semaglutide against Mounjaro and the Wegovy and Mounjaro price comparison go deeper. You can also compare Bydureon against Mounjaro.

07 · Is Byetta the same as Ozempic?

Byetta, Ozempic and Mounjaro are different medicines

Byetta is not the same as Ozempic, and neither is the same as Mounjaro. Byetta is exenatide. Ozempic is semaglutide, and Mounjaro is tirzepatide. Each is a separate active ingredient with its own product information.

The licensing point matters for weight loss. Ozempic is licensed for type 2 diabetes, not as a UK weight-loss medicine, and prescribing it privately for weight loss is off-label. The licensed weight-management options are Mounjaro (tirzepatide) and Wegovy (semaglutide 2.4mg). A regulated UK pharmacy will not supply Ozempic for weight loss.

So for weight loss, Mounjaro vs Ozempic is really Mounjaro vs Wegovy. Our Wegovy pen page shows that option, and our guide to Wegovy strengths against Mounjaro explains how the dose ladders differ.

Wegovy's pens are 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg once weekly. The dose steps up after at least 4 weeks and reaches the 2.4mg maintenance dose from week 17.

08 · Alternatives to Mounjaro

What are the alternatives to Mounjaro?

No licensed medicine is best for everyone; the right one depends on your health, goals and what your prescriber considers appropriate.

• Wegovy (semaglutide 2.4mg): a licensed weight-management injection, once weekly.
• Saxenda (liraglutide): another licensed injectable, supplied at 6mg per millilitre. Unlike Mounjaro and Wegovy, it is a daily injection.
• Wegovy tablets and Foundayo: two GLP-1 weight-loss tablets are now licensed in the UK. Wegovy tablets (oral semaglutide) were approved by the MHRA in June 2026, and Foundayo (orforglipron) in August 2026. They have their own dosing, eligibility checks and trial results, and both are prescription-only.²⁰²¹ Our blog compares Foundayo and Mounjaro.
• Orlistat: a tablet that blocks some dietary fat absorption and produces smaller average losses.
• "Natural GLP-1" supplements such as berberine: these are not medicines, are not regulated for this use and have no comparable trial evidence. They are low-cost supplements with no clinical oversight.

There is no tablet form of Mounjaro; tirzepatide is injection-only in the UK. Our comparisons of alli against Mounjaro and Orlos against Mounjaro cover the orlistat route. If you are weighing prescription tablets, see Duromine against Mounjaro, and for diabetes tablets, metformin against Mounjaro.

You can browse every option on our weight loss treatments page.

09 · Switching safely

Switching to Mounjaro from another injectable

If you are changing from another GLP-1 medicine, the switch should be planned by a prescriber. There is no licensed direct conversion between semaglutide and tirzepatide. Switching is done under prescriber supervision: typically the previous medicine is stopped, a washout interval is observed, and Mounjaro is started at a dose your prescriber judges appropriate. That is often the 2.5mg starting dose, sometimes adjusted based on your history.

Never run two GLP-1 medicines together. 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. If something promises faster results outside a licensed pathway, that is the warning sign. Our page on peptides against Mounjaro explains why.

For exenatide specifically, your prescriber will plan any transition. Tell your prescriber exactly what you are taking and when you last used it.

If you are switching to us at a higher dose, a new customer's first order is £40 off at any dose with code FIRST40. The first-order price at 15mg is £289.99.

10 · Cost and NHS access

Cost, NHS access and how ordering works

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. The NHS 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, which is why many people who meet the licensed criteria choose regulated private treatment rather than waiting.

Privately, the standard price is £169.99 per month at 2.5mg, £218.99 at 5mg, £279.99 at 7.5mg, £290.99 at 10mg, £319.99 at 12.5mg and £329.99 at 15mg. Your first 2.5mg pen costs £129.99 with code FIRST40. Every later order is £25 off the standard price (code DOSE25).

If you step up after 4 weeks on each dose, your first four pens (2.5mg to 10mg) cost £959.96 at standard prices. A first year costs £2,711.88 if you settle at 5mg, up to £3,599.88 at 15mg, before discounts. Across the UK pharmacies we track, Mounjaro pens ranged from £143.96 to £339.00 per month as of 10 October 2026.

Ordering takes four steps:

• Complete a free online consultation, a short health questionnaire with no charge and no 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.
• Our registered pharmacy dispenses it, with same-day dispatch when ordered by 3pm.
• Delivery is free, next-day and tracked, in discreet temperature-controlled packaging.

We supply genuine KwikPens through official LillyDirect supply, and all six doses are in stock. You can start your free consultation whenever you are ready. Mounjaro is a prescription-only medicine supplied only after a consultation reviewed by a GPhC-registered prescriber, and it is used alongside a reduced-calorie diet and increased physical activity. This page is information, not a substitute for medical advice.