Weight Loss Injections: How Long Do You Take Them For? (October 2026)

01 · The short answer

How long do you take weight loss injections for?

You take them for as long as they are working, tolerated and clinically appropriate, and that period is agreed with your prescriber rather than set by a calendar. Mounjaro is licensed for weight management in adults, used alongside a reduced-calorie diet and increased physical activity.¹

Everyone starts on 2.5mg once a week, and the dose then steps up gradually depending on response and tolerability.¹ The main trial followed people for 72 weeks.² Beyond that, the decision is individual.

02 · Your decision

What should you do with this information?

If you are still deciding whether to start, think of treatment as a programme with reviews rather than a short fix. If you are already on treatment, bring your questions about duration to your next review. We cover the wider picture in our guides on how long you can take these injections and using Mounjaro for weight loss.

If you meet the licensed criteria and want to begin, the Mounjaro pen starts with a free online consultation reviewed by a GPhC-registered prescriber. Your first 2.5mg pen costs £129.99 with code FIRST40 (standard price £169.99). Our weight loss clinic explains the full pathway, including monthly reviews.

Related guide: How long can i use mounjaro for weight loss.

03 · How often to inject

How often do you take weight loss injections?

Mounjaro is injected once a week, under the skin, on the same day each week.¹ There is no best time of day: it works the same in the morning or evening, with or without food. What matters is consistency, so choose a day and time you will remember. Many people choose a weekend morning so early side effects fall on days off.¹

Rotate the injection site each week between the stomach area, the front of the thigh, or the back of the upper arm if someone else gives the injection.¹³

Some other weight loss injections work differently. Liraglutide, for instance, is a daily injection, unlike once-weekly Mounjaro and Wegovy. Our practical guide to using Mounjaro weight loss injections walks through the routine step by step.

04 · Missed doses and timing

What if you miss a dose or want to change day?

If you miss a dose, take it as soon as you can within 4 days (96 hours) of the scheduled time, then carry on with your usual day.¹ If more than 4 days have passed, skip the missed dose entirely and take the next one on your normal day. Never take two doses within 3 days of each other.¹

You can change your weekly injection day if needed, as long as at least 3 days (72 hours) have passed since your last dose.¹ Storing the pen correctly also matters for a long course. Keep pens in a fridge at 2–8°C and never freeze them. Once in use, a pen can be kept out of the fridge not above 30°C for up to 30 days, after which it should be discarded.¹³

05 · The first months

What the first months of treatment look like

The early weeks are an adjustment phase, not a verdict. Everyone starts on 2.5mg once a week, and this starting dose is about letting your body adjust, not about weight loss itself.¹ After at least four weeks the dose increases to 5mg, and can then step up by 2.5mg at minimum four-week intervals up to a maximum of 15mg weekly, depending on how you respond and tolerate it.¹

Weight loss on Mounjaro is gradual by design. Losses on 2.5mg are usually modest, and most measurable progress builds from 5mg onward, month by month.² Some people notice appetite change in the first week; others feel little until a higher dose. Both are normal. Early loss includes water weight, so the trend over weeks matters more than any single weigh-in.²

By three months, most people are still on the lower rungs of the dose ladder, so averages at this stage are modest compared with the headline trial figures. Slower early progress does not predict failure, because the dose you respond to may still be ahead of you.² Many people settle at a maintenance dose of 5mg, 10mg or 15mg. Higher is not automatically better, and your prescriber will guide the right pace.¹

06 · What the trial measured

What the trial evidence covers

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, compared with 3.1% with lifestyle changes alone.² These are trial averages, and individual results vary.

A worked example: for someone starting at 100 kg, 20.9% is about 21 kg. That is an average for the 15mg group, not a prediction for you, and not every person needs or reaches that dose.

The trial shows what happens over about a year and a half of treatment. It does not tell you the right end date for your own plan. For that, you rely on your reviews. Our guide to how long you can be on weight loss injections goes into the long-term picture.

07 · The response review

When your prescriber reviews whether to continue

Your response is reviewed rather than assumed. If you have lost less than 5% of your starting weight after 6 months on the highest dose you can tolerate, your prescriber will discuss whether continuing or stopping is right for you.⁴

Note the wording: this is about the highest dose you can tolerate, not simply the time elapsed. Someone who is still working up the ladder has not yet reached that point. This is why we describe duration as individual: the clock that matters is your response and tolerability, not the calendar.

With us, ongoing monthly clinical reviews are included, along with dose-titration and follow-up assessments by the prescribing team. Repeat orders re-check suitability, and nothing ships automatically, so there is a natural checkpoint every time you reorder.

08 · Plateaus

Plateaus are not a reason to stop or double up

Weight loss on Mounjaro is not linear, and plateaus of a few weeks are normal as the body adapts to a lower weight.² Within the licence, the sensible responses are:

• Review food intake honestly, because portions drift back up.
• Protect protein and activity.
• Check the basics, such as sleep and alcohol.
• Ask your prescriber whether a dose step-up is appropriate if you are not yet at maximum.

A plateau is not a reason to double doses or add unlicensed products.¹ Longer-term, judge progress by trend rather than by individual weigh-ins, and use your review to decide whether to continue.

09 · When you stop

What happens when you stop weight loss injections?

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

The medicine works by helping regulate appetite and slowing how quickly the stomach empties, so most people feel fuller sooner and less hungry between meals.¹ That effect depends on the medicine being in your system. As it clears, your appetite may change, so plan for that with your prescriber. Stopping tirzepatide has been studied in SURMOUNT-4: people who stopped after 36 weeks regained on average 14% of body weight over the following year, while those who continued 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.

Building diet and activity habits while you are on treatment is a sensible preparation for coming off it. Talk to your prescriber before stopping, so you can agree whether to step down, continue, or finish.

10 · Health beyond the scales

Why prescribers talk about long-term health

In trials, weight loss on tirzepatide came with average improvements in waist size, blood pressure, cholesterol and blood-sugar measures, and most participants with prediabetes returned to normal blood-sugar levels.² These are trial-average secondary outcomes, not promises.

They are the reason prescribers describe weight management as health management rather than appearance. It also explains why the question of duration is taken seriously: the decision is about your overall health picture, not only the number on the scales.

11 · NHS and private routes

Can you get weight loss injections on the NHS?

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 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. Mounjaro must not be used during pregnancy, and it should be stopped at least one month before trying to conceive. If you become pregnant during treatment, stop the medicine and tell your prescriber promptly.

Whichever route you use, the same principle applies: duration is reviewed by a prescriber. If you are weighing options, our blog guide to weight loss shots in the UK compares how people get them. Cost over a longer course is worth planning: at standard prices, a first year costs £2,711.88 if you stay on 5mg after your 2.5mg starting pen, up to £3,599.88 if you step up through every dose to 15mg. A new customer's first order is £40 less, and every later order is £25 less.