Semaglutide Jabs: How the Weekly Injection Works, Who It's For, and What to Expect

Step 1: what happens when you inject semaglutide

Semaglutide mimics a hormone called GLP-1 (glucagon-like peptide-1) that your gut naturally releases after eating. When you inject it once a week, it binds to GLP-1 receptors in the brain's appetite centres and in the stomach wall. The practical effects are twofold: you feel full sooner, and food moves through your stomach more slowly. Most people notice that portions they would previously have finished comfortably start feeling like too much. That shift in appetite (not a dramatic suppression, but a consistent recalibration) is what drives the weight loss seen in clinical trials.

The injection itself uses a pre-filled pen with a fine needle. You press it against a pinch of skin, press the button, and it's done in seconds. Many people find it easiest to build it into a weekly routine, the same evening each week, pen taken from the fridge door an hour before to reach room temperature. The Wegovy treatment overview covers the pen mechanics in more detail.

The NHS medicines page on semaglutide is a reliable first reference for the plain-language patient information, including injection technique and what to do if you miss a dose.

Step 2: the titration schedule and why it matters

Treatment does not start at the full therapeutic dose. The UK licensed pathway begins at 0.25 mg weekly, moving through 0.5 mg, 1.0 mg and 1.7 mg before reaching 2.4 mg maintenance, with roughly four weeks at each level. This graduated approach exists to let the body adjust; most of the gastrointestinal side effects that people worry about are dose-dependent, and titrating slowly keeps them manageable for the majority of patients.

Since January 2026 a higher 7.2 mg dose has also been available, and the MHRA approved a dedicated single-dose 7.2 mg pen in April 2026, a pre-set weekly injection designed to make the highest-strength option as straightforward as the lower doses. Whether this dose is appropriate for an individual is always a prescriber's decision, made after reviewing progress on lower doses. If you are exploring what semaglutide treatment might look like for you, that conversation starts with a clinical consultation, not a dose selection.

It is also worth knowing that Wegovy and Ozempic both contain semaglutide, but Ozempic is licensed for type 2 diabetes, not weight management. They are not interchangeable. The semaglutide skinny jabs page addresses this confusion directly if you have seen both names mentioned together online.

Step 3: the evidence behind the results

The headline figure most people have seen comes from the STEP 1 trial: around 15% average body-weight reduction over 68 weeks at the 2.4 mg dose, published in the New England Journal of Medicine. That is a population average across a large trial, not a guaranteed individual outcome, some participants lost considerably more, some less. Results depend on diet, activity levels, adherence to the titration schedule and individual biology.

A newer head-to-head trial, SURMOUNT-5, compared tirzepatide (Mounjaro) directly with semaglutide 2.4 mg and found tirzepatide produced greater average weight loss over 72 weeks. Both medicines are effective; which suits a given person is a clinical question, not a marketing one. The fat jabs comparison page sets out the two approaches side by side if that question is on your mind.

Cost is a real consideration for many people exploring private treatment. The weight-loss jabs cost guide explains what private prices typically include and what to watch out for when comparing quotes online, consultation fees, prescription charges and aftercare support can vary significantly between providers.

Step 4: eligibility, safety and next steps

The UK licence for Wegovy covers adults with a BMI of 30 or above, or a BMI of 27 to 29.9 alongside at least one weight-related condition such as high blood pressure, high cholesterol, type 2 diabetes or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. BMI alone is not sufficient for approval; a prescriber reviews your full medical history, current medicines and any contraindications before making a decision.

The most common side effects are gastrointestinal, nausea, loose stools, constipation, indigestion and occasional vomiting are all reported, particularly in the early weeks or after a dose increase. For most people they settle. More serious but less common concerns include pancreatitis; the MHRA issued a Drug Safety Update in January 2026 highlighting that severe, persistent stomach pain radiating to the back should prompt urgent medical attention. Anyone considering Wegovy jabs should know they can report suspected side effects directly at the MHRA Yellow Card scheme.

Semaglutide jabs are not recommended during pregnancy, whilst breastfeeding, or if you are actively trying to conceive. They are not licensed for under-18s. If you take an oral contraceptive pill and start tirzepatide (a different jab in this class), there are specific additional contraception steps required, your prescriber covers this at consultation.

If you want to understand how a supervised weight-loss treatment plan might be structured for you, a free consultation with a GPhC-registered prescriber is the right place to start. Our clinical team reviews every consultation personally, no automated decisions.