Why your weight loss injections might not be working — and what to do next

Are your expectations aligned with how these medicines actually work over time?

The most common source of disappointment is a mismatch between what people expect to see and the timeline the medicine actually operates on. The large SURMOUNT-1 clinical trial, published in the New England Journal of Medicine, reported average weight reductions of around 20–21% with tirzepatide at 15 mg over 72 weeks. Seventy-two weeks is nearly a year and a half. In the first four to eight weeks, many people notice appetite changes before the scales shift. If you are at week three and feel the injections are doing nothing, you may simply be measuring too early.

It also helps to understand what the injections are actually doing biologically: slowing gastric emptying, reducing appetite signals, and improving the hormonal environment around blood sugar regulation. None of those changes show up on a scale overnight. Tracking hunger levels, portion sizes and energy rather than daily weight often gives a clearer picture of whether the medicine is working at a physiological level.

If you are further into treatment and progress has genuinely plateaued, that is a different question, and if you want to explore the reasons in more detail you can read about why weight loss injections sometimes stop working as expected before raising it with your prescriber rather than quietly assuming the medicine has failed.

Is your dose doing what it is supposed to do at this stage?

The titration schedule exists for a reason. With tirzepatide, treatment begins at 2.5 mg, a dose whose job is to help your system adjust and reduce the chance of nausea, not to drive substantial weight change. The same principle applies to the early steps of the semaglutide (Wegovy) schedule. If you are still on the starting dose several months in and expecting the results seen at the top of the schedule, the dose itself may be the explanation rather than the medicine.

Dose increases should be guided by your prescriber, with evidence of how you have responded at each step. At nume, every repeat order is clinically re-reviewed, dose changes are not automated. If you have been on the same dose for longer than planned and are not seeing progress, that is exactly the conversation to have at your next clinical review. You can also read about how long weight loss injections typically take to show results to calibrate what is realistic at your current dose.

Separately, if you have recently switched from one medicine to another, the early steps of the new schedule reset the clock on titration. Progress at week four on a new medicine is not comparable to week twenty on the previous one.

Could a storage or administration issue be reducing the medicine's effectiveness?

This is the factor people least often consider, and it is more common than the data suggest, because patients rarely know there is a problem. GLP-1 pens must be stored refrigerated at 2–8°C until opened. If a pen is left out in a warm car, placed near a heat source, or kept in a gym bag through a summer commute, the active medicine can degrade before it is injected. The pen itself shows no visible sign of this; it looks identical.

A practical anchor: keeping your pen in the fridge door, the same spot every week, makes it easier to check it has stayed cool and easier to build the Sunday-evening injection into a routine. Once a pen has been opened, the room-temperature window detailed in the Patient Information Leaflet applies, always check that leaflet, because the window differs between products and the specifics are the prescriber's domain, not something to rely on a website for.

Injection technique also matters. Rotating sites (abdomen, thigh, upper arm) and using a fresh needle each time helps absorption consistency. If you are reusing needles or always injecting the same spot, both can affect how the medicine enters your system. Using a fresh needle for every injection is the straightforward fix there.

When is it right to ask your prescriber, or reconsider the medicine altogether?

Some people reach a genuine plateau where titration to the highest tolerated dose has happened, lifestyle factors are in order, and weight loss has stalled for several months. NICE guidance for tirzepatide notes that if less than 5% weight loss has occurred after six months at the highest tolerated dose, continuing is subject to clinical review. That is not a rule that says treatment has failed, it is a checkpoint that prompts a proper clinical conversation. Your prescriber can assess whether a dose adjustment, a different medicine, or additional support makes sense, and it may also be worth looking at which weight loss injections tend to produce results most quickly to inform that conversation. Those who prefer to avoid injections entirely can read about oral weight loss medicines available in the UK as an alternative route.

It is also worth noting that weight management medicines work best alongside reduced-calorie eating and regular activity, that is written into their licensed use, not a caveat. If eating patterns have drifted, or sleep or stress levels have changed significantly, those factors interact with the medicine's effectiveness in ways a prescriber can help you think through. Common clinical questions about weight loss treatment are answered in our FAQs if you want a quick reference before speaking to the team.

If you are concerned that your treatment is not working as it should, the right next step is a clinical review. Check your eligibility and speak to our prescribers through our free consultation. A real clinician (not an automated queue) reads your answers and responds the same day.