The Weekly Weight Loss Injection Explained

You've heard about the injection. Here's what the first few weeks actually feel like.

Most people arrive at this page having already read something, a news article, a friend's experience, a social media post. That's a reasonable place to start, and it's also the reason a lot of people come in with questions that the headlines skipped over.

The weekly injection is given into the fatty tissue just under the skin: the abdomen, the outer thigh, or the upper arm. You rotate sites week to week. The pen is pre-filled, so there's no drawing up of liquid and no measuring. Most people describe the injection itself as a mild sting that passes in seconds. The needle is very fine.

What changes in the days after isn't immediate or dramatic. The medicines work by mimicking gut hormones (GLP-1 in the case of Wegovy, both GIP and GLP-1 with Mounjaro) that signal fullness to the brain and slow the rate at which food leaves your stomach. You may notice you feel satisfied sooner at meals, or that you think about food less between them. For many people the shift is gradual rather than sudden. Nausea is common, particularly after starting or after a dose increase; it usually settles within a couple of weeks. The broader overview of weight loss injection treatment covers the side-effect picture in more detail.

The first dose (2.5mg for Mounjaro, 0.25mg for Wegovy) is set deliberately low. Its job is adjustment, not treatment. The prescriber builds the dose over months until you reach the level that's clinically appropriate for you.

Who the weekly injections are licensed for in the UK

If you're wondering whether you'd qualify, the honest answer is: a prescriber decides that, not a checklist. That said, the licensed criteria give a useful starting frame.

Both Mounjaro and Wegovy are licensed for adults with a BMI of 30 or above, or a BMI of 27 or above if you have at least one weight-related health condition such as high blood pressure, type 2 diabetes, high cholesterol or obstructive sleep apnoea. For people from South Asian, Chinese, Middle Eastern, Black African or African-Caribbean backgrounds, UK guidance sets the thresholds 2.5 kg/m² lower. NICE has appraised both medicines and its guidance sets out the conditions under which NHS prescribing applies; those criteria are stricter and more specific than the licensed eligibility alone. You can check your BMI using the NHS BMI calculator as a rough starting point.

Age matters too. Neither medicine is licensed for people under 18. Pregnancy, breastfeeding and actively trying to conceive are situations where neither is recommended, a conversation with your GP or prescriber matters here. Certain conditions, including a history of pancreatitis or medullary thyroid cancer, also require careful prescriber review. The relationship between these injections and diabetes is a related area worth reading if that's part of your picture.

The consultation at nume is where this gets properly assessed. A GPhC-registered Independent Prescriber reads your answers personally, your health history, your medications, your goals. That review happens the same day.

What the evidence says, and what it doesn't promise

The trial results for weekly weight loss injections are, genuinely, stronger than anything that's come before in this space. In the SURMOUNT-1 trial (2,539 adults with obesity, 72 weeks), tirzepatide at its highest dose produced an average body-weight reduction of around 20–21%, as reported in the New England Journal of Medicine. The STEP 1 trial for semaglutide 2.4mg, also published in the NEJM, showed around 15% average reduction over 68 weeks. These are averages across large populations. Individual results vary, some people lose more, some less, and the medicine works alongside a reduced-calorie diet and increased activity, not instead of them.

There's also the question of what happens if you stop. Weight tends to return after discontinuation for most people, which is why these medicines are considered long-term treatments rather than short courses. That's a decision worth discussing with a prescriber rather than making on the basis of a blog post.

If you're weighing up the financial side of private treatment, the cost of weight loss injections in the UK page gives an honest breakdown of what typical private pricing looks like and what it should include.

Getting started: the route that's actually available to you

There are two routes in the UK. The NHS route runs through your GP or a specialist weight management service; eligibility criteria are strict and waiting times can be long, depending on where you live and which medicine is being considered. The private route (through a pharmacy like nume) removes the waiting list and the referral requirement, but does not remove the clinical assessment. It cannot. These are prescription medicines.

At nume, the process is straightforward. You complete a consultation, which is reviewed the same day by a real prescriber. Identity is verified, weight is confirmed on video, and your GP is notified in line with GPhC guidance. If treatment is clinically suitable and you order before noon on a working day, your pen is dispatched the same day and arrives the next working day via DPD, tracked, in plain packaging. If you'd like to read more about how the dosing schedule works in practice, our page on once a week injection for weight loss walks through what to expect across the treatment period.

If you have questions before you start, the common questions page covers the things most people ask first. And if you're curious about the clinical team behind the service, our lead prescriber's profile is there to read.

Choosing a weekly weight loss injection is a medical decision, not a shopping one. It deserves a proper clinical conversation, and if the cost of getting started is a concern, you can also spread the payment for weight loss injections using Klarna at checkout. If you're ready to have that conversation, start your free consultation and a prescriber will review your situation the same day.