Main Difference Between Semaglutide and Tirzepatide (October 2026)

01 · The short verdict

Which suits you: semaglutide or tirzepatide?

Neither is simply "better" for everyone, but tirzepatide produced larger average weight loss than semaglutide 2.4mg in the first large head-to-head trial. In SURMOUNT-5, 751 adults took one or the other for 72 weeks, and average loss was 22.8 kg on tirzepatide versus 15.0 kg on semaglutide.¹⁵ Both are effective, licensed treatments, and which suits you depends on your health profile, tolerance and prescriber advice, not the headline number alone.¹⁵

Tirzepatide (Mounjaro) is a once-weekly injection with a six-step dose ladder from 2.5mg to 15mg; your prescriber decides whether it suits you. You can see current options on our Mounjaro pen page, where all six doses are in stock.

Semaglutide (Wegovy) is a once-weekly injection with a dose ladder ending at 2.4mg; your prescriber decides whether it suits you. Our Wegovy pen page shows the first-pen price, £99.99 as a first-order price.

The decision is made with a prescriber. Our free consultation is reviewed by a GPhC-registered prescriber, who can discuss which option fits your history. You can start your free consultation without obligation.

02 · Side by side

Semaglutide vs tirzepatide at a glance

03 · How to choose

The decision factors that matter

Five factors usually decide the choice, and your prescriber will weigh them with you.

• Size of the average result. Tirzepatide was ahead in SURMOUNT-5. Trial averages do not predict your own result.
• Tolerance. Both medicines slow stomach emptying and can cause digestive side effects, so how you cope matters as much as the average.
• Licence and history. Semaglutide for weight loss means Wegovy, not Ozempic.¹⁸
• Dose ladder. Mounjaro has six steps and Wegovy five, each stepped up over time with prescriber review.
• Cost. A new customer's first order is £40 less and every later order £25 less.

For a plain-English walk through the brand names, see our guide to Wegovy versus Mounjaro in the UK.

Related guide: Main difference between mounjaro and wegovy.

Related guide: Is there a difference between mounjaro and tirzepatide.

04 · How they work

How semaglutide and tirzepatide work

Tirzepatide activates two natural gut-hormone receptors at once, GIP and GLP-1, while semaglutide is a single-action GLP-1 medicine.¹ That dual action is what distinguishes Mounjaro from semaglutide products such as Wegovy and Ozempic.¹

Together, these hormone signals help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin. In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹

Neither medicine replaces diet and activity. Both are used alongside a reduced-calorie diet and increased physical activity.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

05 · What the trials show

What the trials show: SURMOUNT-5, STEP 1 and SURMOUNT-1

The first large head-to-head comparison is SURMOUNT-5, where tirzepatide beat semaglutide 2.4mg on average weight loss. Adults on tirzepatide lost 20.2% of body weight over 72 weeks versus 13.7% on semaglutide 2.4mg (Wegovy).¹⁵

The detail shows how the groups split. At least 10% of body weight was lost by 81.6% on tirzepatide versus 60.5% on semaglutide. At least 15% was lost by 64.6% versus 40.1%, at least 20% by 48.4% versus 27.3%, and at least 25% by 31.6% versus 16.1%.¹⁵ Average loss was 22.8 kg versus 15.0 kg.¹⁵

As a worked example only: for someone starting at 100 kg, 20.2% is about 20 kg and 13.7% is about 14 kg. Individual results vary.

Semaglutide's own trial. In STEP 1, adults on semaglutide 2.4mg lost on average 14.9% of body weight over 68 weeks, compared with 2.4% on placebo.⁹ In that trial, 86.4% lost at least 5% of body weight (31.5% on placebo), 69.1% lost at least 10% (12.0% on placebo) and 50.5% lost at least 15% (4.9% on placebo).⁹

Tirzepatide's own trial. In SURMOUNT-1, 2,539 adults on tirzepatide alongside diet and exercise lost on average 15% of body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, compared with 3.1% with lifestyle changes alone.² At 72 weeks, 85% on 5mg, 89% on 10mg and 91% on 15mg had lost at least 5% of body weight, and half on 10mg and 57% on 15mg lost at least 20%.²

STEP 1 and SURMOUNT-1 were separate trials with different designs, so their numbers should not be set against each other. Use SURMOUNT-5 for the direct comparison. These are trial averages, and individual results vary. Treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.²

06 · Doses and titration

Dosing and titration: six steps versus five

Both medicines are injected once a week and both are stepped up gradually. Mounjaro comes in a multi-dose KwikPen in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ Wegovy pens are 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg. The dose steps up after at least 4 weeks, reaching the 2.4mg maintenance dose from week 17.¹⁸

The mg numbers are not comparable. Tirzepatide and semaglutide are different molecules, so 2.4mg of one is not equivalent to 2.4mg of the other.

On cost, the first four pens of Mounjaro (four pens: 2.5mg, 5mg, 7.5mg and 10mg) come to £879.96 at standard prices. A first year costs £2,399.88 if you settle at 5mg, up to £3,279.88 at 15mg. A new customer's first order is £40 less with code FIRST40, and every later order is £25 less (code DOSE25). Our semaglutide and tirzepatide discount guide has the current details.

Switching providers or products mid-course should always be done with a prescriber, not by estimating an equivalent dose yourself.

07 · Drawbacks and side effects

Drawbacks of tirzepatide and semaglutide

Both medicines share the same broad drawbacks: they are prescription-only, they work alongside diet and activity, and they can cause side effects. For tirzepatide, the practical drawbacks are that it is injection-only in the UK, it is a long-term commitment, and cost is ongoing.¹ Its slowing of stomach emptying is part of how it works.¹

For semaglutide, STEP 1 reported gastrointestinal side effects in 74.2% of people on semaglutide 2.4mg, compared with 47.9% on placebo. Overall, 7.0% stopped treatment because of side effects, compared with 3.1% on placebo.⁹

If you notice a new symptom on either medicine, tell your prescriber and report it through the Yellow Card scheme.¹⁹

08 · Muscle, belly fat and feeling good

Muscle loss, belly fat and "feeling good" on treatment

The trials report overall body-weight loss, not a split between fat and muscle. Anyone worried about muscle should ask their prescriber and keep up regular physical activity, which treatment is designed to accompany.²

The same applies to belly fat. Neither medicine can be targeted at one part of the body.

On "why do I feel so good on semaglutide", the honest answer is that it varies. Many people report feeling fuller and less hungry, which is how this class of medicine is designed to work.¹

The question "did I lose more on semaglutide than tirzepatide" has a personal answer. Averages in SURMOUNT-5 favoured tirzepatide, but trial averages do not predict your own result.¹⁵

09 · Ozempic and tablets

Licensing: Ozempic, Wegovy, tablets and "poor man's Ozempic"

Ozempic is semaglutide licensed for type 2 diabetes, so it is not a UK weight-loss medicine, and prescribing it privately for weight loss is off-label.¹⁸ The licensed weight-management options are Mounjaro (tirzepatide) and Wegovy (semaglutide 2.4mg). A "semaglutide versus tirzepatide" decision for weight loss is therefore really Wegovy versus Mounjaro, and a regulated UK pharmacy will not supply Ozempic for weight loss.¹⁸

There is no tablet form of Mounjaro. Two GLP-1 weight-loss tablets are now licensed in the UK: Wegovy tablets (oral semaglutide, approved by the MHRA in June 2026) and Foundayo (orforglipron, approved in August 2026).²⁰²¹ They are different medicines from Mounjaro, with their own dosing, eligibility checks and trial results, and both are prescription-only. For tablet pricing, see the weight loss treatments hub and the product pages.

The phrase "poor man's Ozempic" is marketing, usually for supplements such as berberine. These are not medicines, are not regulated for this use and have no comparable trial evidence.¹ They are low-cost supplements with no clinical oversight, and dosing is not standardised. They are not a substitute for either semaglutide or tirzepatide.

Orlistat, a tablet, blocks some dietary fat absorption and produces smaller average losses. Saxenda (liraglutide) is a daily injection, unlike once-weekly Mounjaro and Wegovy. Our guide to liraglutide, semaglutide and tirzepatide compares all three.

10 · Switching and mixing

Switching between them, and what not to mix

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. This is often the 2.5mg starting dose, sometimes adjusted based on your history.¹¹

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.⁷ If something promises faster results outside a licensed pathway, that is the warning sign.

If you are switching to us from another provider at a higher dose, your first order is still £40 less with code FIRST40. At 15mg, for example, a first order is £259.99 as a first-order price. For other medicines and supplements you take, tell your prescriber during the consultation so they can check suitability. We supply genuine KwikPens through official LillyDirect supply, direct from Eli Lilly's UK distribution.

11 · 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

12 · NHS or private

NHS or private access to these medicines

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.

NHS access to Wegovy runs through specialist weight-management services; ask your GP.

Privately, ordering with us takes three steps. First, a free online consultation, which is a short health questionnaire with no charge and no obligation. Second, a review by a GPhC-registered prescriber; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full. Third, dispensing by our registered pharmacy, with same-day dispatch when ordered by 3pm and free next-day tracked delivery in discreet, temperature-controlled packaging.

The price shown is the price paid. We include needles, a sharps bin and injection guidance with every order, and ongoing monthly reviews with the prescribing team. Mounjaro is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber. Individual results vary, and this page is information, not a substitute for medical advice.