Weight Loss Injections: How Many Shots, and How Often?

One shot a week: what the trial data actually show

The pivotal SURMOUNT-1 trial, published in the New England Journal of Medicine, placed participants on once-weekly tirzepatide for 72 weeks. Not twice weekly, not a loading burst of several injections, one shot, every seven days. The same rhythm governed the STEP 1 semaglutide trial at 68 weeks. This weekly cadence is built into the licensed schedule for both medicines because the compounds have long half-lives, meaning each dose is still active when the next one arrives. That pharmacology is also why missing a shot by a day or two matters less than, say, missing a daily tablet, though your prescriber and leaflet set out exactly what to do if you miss one.

Over those trial durations, participants using tirzepatide at the highest tolerated dose lost around 20–21% of their body weight on average. Semaglutide 2.4 mg produced roughly 15% average loss over 68 weeks. Both figures come from controlled conditions with lifestyle support alongside the injections, so they are benchmarks rather than personal predictions.

If you are still weighing up whether this approach is right for you, our guide to injection shots for weight loss covers how these medicines work and what to consider before starting.

The practical upshot: you are committing to a once-weekly routine, not an intensive injection course that ends after a few weeks.

How dose steps change what you inject, without changing how often

A question our prescribers hear most weeks is whether higher doses mean more frequent shots. They do not. Mounjaro starts at 2.5 mg (a strength chosen to help your system adjust rather than to drive weight loss) and is titrated upward, typically in four-week steps, through 5, 7.5, 10, 12.5 and up to 15 mg. The pen changes; the weekly schedule does not. Wegovy follows a similar ladder: 0.25 mg rising through 0.5, 1.0, 1.7 and 2.4 mg, with the newer 7.2 mg dose now also approved in the UK for eligible patients.

What this means in practice is that the early months feel manageable because the dose is low and side effects tend to be mild. As titration progresses, some people notice more nausea around each step-up; that usually settles within a week or two. The NHS tirzepatide medicines page gives a plain-English overview of what to expect at each stage, and it is worth reading before you start.

Your prescriber decides when (and whether) each step-up is right for you. Evidence of how you are tolerating the current dose, and of actual weight change, feeds into that review. At nume, every repeat order is clinically re-reviewed before it is dispensed.

How long do you keep injecting? Treatment duration in the evidence and in practice

There is no universally fixed course length for these medicines. NICE's guidance on tirzepatide (TA1026) notes that if less than 5% weight loss has occurred after six months at the highest tolerated dose, continuing treatment should be reviewed. That is the clearest official stopping marker, and it implies the inverse: if treatment is working and tolerated well, it continues beyond six months. Many people use these medicines for considerably longer than the trial windows.

For those accessing Wegovy through the NHS under NICE's TA875 recommendation, treatment is capped at two years within a specialist weight management service. Private prescribing does not carry that automatic ceiling, but it does require ongoing clinical review, weight, tolerability and overall health picture each time. The question of how many injections you need overall therefore depends heavily on individual response, starting point and clinical goals.

Cost is a factor for many people, and understanding the full cost of weight loss injections in the UK is a sensible part of planning treatment that might run for a year or more. A legitimate price covers the prescription, clinical oversight and delivery, not just the pen.

Injection site, rotation and what to do between shots

Each weekly shot goes into subcutaneous tissue: the abdomen, outer thigh or upper arm are the licensed sites for both medicines. Rotating the spot within those areas (rather than injecting the same square centimetre every week) reduces the chance of localised skin reactions. Choosing where to inject is worth reading if you are deciding between sites or wondering whether one is more comfortable than another.

Between injections the pen is stored in the fridge at 2–8°C. The exact window during which the pen can be kept at room temperature if you are travelling or the fridge is unavailable varies by product and pen format, the Patient Information Leaflet is the authoritative source for that detail, not a general article. Each Mounjaro KwikPen contains four doses, one per weekly injection; you use the same pen across four weeks, then start a new one. Wegovy uses a separate pre-filled pen per injection.

If you use sharps disposal, a 1-litre sharps container is the standard choice for home needle disposal and keeps used needles safely contained between collections.