# Mounjaro vs Wegovy: two weekly injections, two different drugs Updated 24 August 2026 ยท Written by the Penwise team Mounjaro and Wegovy get filed together because they are both weekly injections prescribed for weight, and that similarity hides most of what matters. One is tirzepatide, which acts at two receptors. The other is semaglutide at its weight-management dose, which acts at one. They titrate differently, they clear at different speeds, their pens run on different clocks, and the head-to-head trial did not call it a draw. ## The short version | | Mounjaro | Wegovy | | --- | --- | --- | | Molecule | Tirzepatide | Semaglutide | | Receptors | GIP and GLP-1 | GLP-1 | | Cadence | Weekly | Weekly | | Half-life | About 5 days | About 7 days | | Dose ladder | 2.5 to 15 mg in 2.5 mg steps | 0.25, 0.5, 1.0, 1.7, 2.4 mg | | Steps to the top | 5 increases | 4 increases | | Pen | KwikPen, 4 doses, 30-day window | FlexTouch, 4 doses, 42-day window | | Also sold as | Zepbound in the United States | Ozempic at diabetes doses | Both are prescription-only and licensing differs by country. What your prescriber can write depends on where you are and why you are being treated. ## One receptor or two Semaglutide is a GLP-1 receptor agonist. It mimics a gut hormone that slows stomach emptying, prompts insulin release when glucose is high, and reduces appetite through receptors in the brain. Tirzepatide does that and adds GIP receptor activity. GIP is a second incretin hormone, and stimulating it alongside GLP-1 appears to produce more weight loss than GLP-1 alone at the doses studied. The mechanism is still being argued over in the literature. The clinical difference is not. > The dual mechanism is not a free upgrade. Two receptor pathways is also two routes to gastrointestinal side effects, and the titration schedule is longer as a direct result. ## The head-to-head result Most comparisons put two separate trials next to each other, which is weak evidence because the populations differ. There is a direct comparison. SURMOUNT-5 randomised adults with obesity to tirzepatide or semaglutide at their maximum tolerated doses and ran for 72 weeks. - **20.2%**: Average weight loss on tirzepatide at 72 weeks - **13.7%**: Average weight loss on semaglutide at 72 weeks - **72 weeks**: Trial length, both arms That gap is consistent with the separate trials: SURMOUNT-1 put tirzepatide at around 20.9% at 72 weeks, and STEP-1 put semaglutide 2.4 mg at around 14.9% at 68 weeks. Three studies, the same ordering. What the averages do not tell you is where you personally land. The spread inside each arm is enormous. Plenty of people on semaglutide lose more than the tirzepatide average, and plenty on tirzepatide never reach the semaglutide one. An average is a fact about a trial population, not a forecast for one person. ## The shape of the week is different Seven days versus five days of half-life sounds like a footnote and is the thing you actually feel. Semaglutide at a seven-day half-life falls to roughly half its peak by the time the next dose is due, so the curve across the week is comparatively flat. Tirzepatide at five days is down to about two fifths, so the same weekly rhythm produces a deeper trough. People switching from Wegovy to Mounjaro often describe appetite coming back late in the week, and that is the arithmetic, not imagination. It runs the other way at the start too. Steady state arrives after roughly four to five half-lives: about four weeks for tirzepatide, four to five for semaglutide. Neither drug is doing its full job in week one, which is why judging either on the first fortnight tells you almost nothing. The [tirzepatide](https://penwiseapp.com/en/guides/how-long-does-mounjaro-stay-in-your-system) and [semaglutide](https://penwiseapp.com/en/guides/how-long-does-ozempic-stay-in-your-system) decay tables show the full week-by-week picture. ## Titration: five steps against four Mounjaro starts at 2.5 mg and climbs in 2.5 mg increments to 15 mg, with four weeks minimum at each step. From first injection to top dose is five increases and at least twenty weeks. Wegovy starts at 0.25 mg and moves through 0.5, 1.0 and 1.7 to 2.4 mg on the same four-week cadence. Four increases, sixteen weeks minimum. Neither ladder is a target you must reach. Both are designed so the dose can stop wherever the effect is good and the side effects are tolerable, and a great many people settle below the top rung and stay there. What matters for tracking is that a dose increase resets the clock: the fortnight after a step up is when [side effects](https://penwiseapp.com/en/guides/glp-1-side-effects-timeline) cluster, and the four weeks after it is when the new steady state arrives. See the [full titration schedules](https://penwiseapp.com/en/guides/glp-1-dose-schedule) for both. ## The pens are not interchangeable A Mounjaro KwikPen holds four weekly doses and may be used for 30 days from first injection. Four weekly doses take 28 days, so the slack is two days. Shift a shot twice and the last dose falls outside the window. A Wegovy FlexTouch also holds four doses and allows 42 days, so the same four weeks of medicine sits inside a fortnight of margin. Wegovy is also sold in the single-dose pen format in several markets, where the question does not arise at all. Dialling is different too: the FlexTouch counts 37 clicks at the lower strengths and 75 at 2.4 mg, while the KwikPen delivers one fixed 0.6 ml dose over 60 clicks. Neither number is guesswork, and both are in the [pen click chart](https://penwiseapp.com/en/guides/glp-1-pen-click-chart). The discard clocks are in [how long a pen lasts](https://penwiseapp.com/en/guides/how-long-does-a-glp-1-pen-last). ## Switching between them Switching is a prescriber decision and the practical points are consistent. You do not carry your dose across, because the ladders are not equivalent and 2.4 mg of semaglutide is not 15 mg of tirzepatide in any meaningful sense. Most switches restart titration lower than where you finished, and the first weeks after a switch look like starting over because pharmacologically they are. The old drug is also still in you. Semaglutide takes about five weeks to clear and tirzepatide about 25 days, so for the first fortnight after a switch you are experiencing a decaying level of one drug and a rising level of the other at the same time. That overlap explains a lot of the confusing reports people give about their first month. - Keep one continuous record across the switch rather than starting a fresh log. The comparison you will want in six months is against your old dose, not against day one of the new one. - Expect the weekly rhythm to change even at a comparable effect, because the half-lives differ. - Note the reason for the switch. Side effects, availability, cost and plateau all produce different follow-up conversations. - Watch weight weekly rather than daily through the transition, because the first fortnight is noisy for reasons that have nothing to do with fat. ## Which one is not a question this page can answer Availability, licensing, what your prescriber will write, cost, what you tolerate and what your history is all outrank a trial average, and none of them are visible from here. What is worth carrying into that conversation is your own record: the doses you have been on, how long each lasted, what the side effects looked like at each step, and what your weight actually did rather than what you remember it doing. Penwise tracks both drugs the same way, with the right half-life, the right pen, the right ladder and the right in-use window for each, and it will keep one unbroken history if you move between them. **Track either one properly, and the switch too** Correct pharmacokinetics for tirzepatide and semaglutide, every pen, and a history that survives a change of drug. Free core tracker, no account. ## Common questions **Is Mounjaro better than Wegovy for weight loss?** In the direct comparison, SURMOUNT-5, tirzepatide averaged 20.2% weight loss at 72 weeks against 13.7% for semaglutide, and the separate trials point the same way. That is an average across a trial population, and individual results inside both arms varied enormously. **Are Mounjaro and Wegovy the same drug?** No. Wegovy is semaglutide, which acts at the GLP-1 receptor. Mounjaro is tirzepatide, which acts at both the GIP and GLP-1 receptors. They are different molecules with different dose ladders, different half-lives and different pens. **Can I switch from Wegovy to Mounjaro?** That is a prescriber decision. When it happens, the dose does not carry across, because the ladders are not equivalent, and most switches restart titration. Expect an overlap period as one drug clears while the other builds. **Which has worse side effects, Mounjaro or Wegovy?** Both are dominated by gastrointestinal effects that cluster in the days after a shot and in the fortnight after a dose increase. Tirzepatide has a longer ladder, so there are more of those increase windows to get through. Which one an individual tolerates better is not predictable in advance. **Why does my appetite come back at the end of the week on Mounjaro but it did not on Wegovy?** Tirzepatide has a half-life of about five days against semaglutide at about seven, so the same weekly interval produces a deeper trough before the next dose. The end-of-week difference is a real pharmacokinetic effect. **Is Zepbound the same as Mounjaro?** Yes, the same molecule in the same device, sold under a different name for a different licensed indication in the United States. Nothing about the dose ladder, the pen or the pharmacokinetics changes. ## Sources Every factual claim on this page traces to the product information a regulator publishes, or to a published trial. Links open on the site of whoever issued the document. - [Mounjaro: EPAR product information](https://www.ema.europa.eu/en/medicines/human/EPAR/mounjaro), European Medicines Agency - [Wegovy: EPAR product information](https://www.ema.europa.eu/en/medicines/human/EPAR/wegovy), European Medicines Agency - [Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1)](https://doi.org/10.1056/NEJMoa2206038), New England Journal of Medicine, 2022 - [Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1)](https://doi.org/10.1056/NEJMoa2032183), New England Journal of Medicine, 2021 - [Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5)](https://doi.org/10.1056/NEJMoa2416394), New England Journal of Medicine, 2025 Penwise is a tracking and education tool, not a medical device. Nothing on this page is medical advice, a diagnosis or a recommendation to start, stop or change a dose. Dosing decisions belong to you and your clinician. Ozempic, Wegovy, Rybelsus, Saxenda and Victoza are trademarks of Novo Nordisk; Mounjaro, Zepbound and Trulicity are trademarks of Eli Lilly. Penwise is not affiliated with, endorsed by or connected to either company. ## Keep reading - [Mounjaro vs Ozempic: what actually differs](https://penwiseapp.com/en/guides/mounjaro-vs-ozempic): Two receptors versus one, five days of half-life versus seven, six fixed strengths versus a dial. A comparison of the things that change your week. - [Zepbound vs Mounjaro: the same drug with two labels](https://penwiseapp.com/en/guides/zepbound-vs-mounjaro): Identical molecule, identical device, identical ladder. What actually differs is the licence on the box, and that turns out to matter for cost, supply and paperwork. - [A Wegovy tracker built around the sixteen-week climb](https://penwiseapp.com/en/guides/wegovy-tracker): Tracking Wegovy (semaglutide) for weight management: the five-step titration, both pen designs, and reading the weight trend against the dose you were actually on. - [GLP-1 dose schedules: every ladder, and why the steps are four weeks](https://penwiseapp.com/en/guides/glp-1-dose-schedule): The titration ladder for every GLP-1 product side by side, and the pharmacology that decides how long each step has to last.