Common Weight Loss Injections Available in the UK

Step 1, The prescription process: how treatment actually starts

Before a single pen is dispensed, a prescriber reviews your medical history, current medicines, weight, and any relevant conditions. That clinical step is not a formality. These are prescription-only medicines under the Human Medicines Regulations 2012, which means no legitimate pharmacy sends them out on the basis of a self-declaration alone. At nume, a GPhC-registered Independent Prescriber reads every consultation personally, the same day it is submitted.

Identity and weight are verified, not estimated. Transfer patients bringing a current treatment from another provider submit evidence of that; anyone moving to a higher dose does the same. Once approved, the pen is dispatched same-day (for orders submitted before midday, Monday to Friday) and arrives the next working day via tracked DPD delivery. Plain packaging, no branding visible from the outside.

The GPhC register lets you check any online pharmacy in under a minute. It is worth doing before you hand over any personal details to a provider you have not used before. Our premises registration number is 9012878, verifiable directly at the GPhC pharmacy register.

Step 2, Starting doses and titration: what the schedule actually looks like

Both injections begin well below their maintenance dose. Tirzepatide starts at 2.5 mg, a dose whose job is adjustment, not weight loss. Its purpose is to let your digestive system settle before the dose climbs. Semaglutide (Wegovy) begins at 0.25 mg for the same reason. Prescribers typically step each up roughly every four weeks, reviewing tolerance at each stage.

Tirzepatide runs through six strengths: 2.5, 5, 7.5, 10, 12.5 and 15 mg. Semaglutide's Wegovy pathway reaches 2.4 mg as the established maintenance dose; a 7.2 mg single-dose pen was approved by the MHRA in April 2026 for adults with a BMI of 30 or above. For a detailed look at how the weekly schedule sits in everyday life, our overview of weight loss injections covers practical questions about timing and routine.

Titration is not a race. Rushing past a dose that is causing significant nausea rarely helps. The prescriber, not the patient, judges when a step up is appropriate, which is one reason clinical re-review before every repeat order matters rather than being a box-ticking exercise. You can find common questions about the process answered on our FAQ page.

Step 3, Side effects to expect and the ones that need prompt attention

Gastrointestinal effects are the most reported across both medicines: nausea, diarrhoea, constipation, indigestion, and occasionally vomiting. These tend to be most noticeable in the days after starting or stepping up a dose, and most people find them manageable and short-lived. Fatigue and headache are also reported, particularly early on. A full breakdown is available on our guide to common side effects of weight loss injections.

The side effects that need same-day medical help are different in character: severe stomach pain that extends to the back (a potential sign of pancreatitis, flagged in an MHRA Drug Safety Update in January 2026), signs of a serious allergic reaction, or symptoms of significant dehydration after repeated vomiting. The NHS medicines page for tirzepatide sets out the full list clearly and is worth bookmarking when you start treatment.

Both medicines carry a Black Triangle (▼) designation, meaning the MHRA collects additional safety data while they are in widespread use. Patients can report any suspected side effect through the MHRA Yellow Card scheme, and are actively encouraged to do so.

Who these injections are licensed for, and what the trial evidence shows

Both medicines are licensed for adults with a BMI of 30 or above, or 27 and above when a weight-related condition is present, high blood pressure, high cholesterol, type 2 diabetes, obstructive sleep apnoea, and several others each qualify. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. A BMI figure alone does not determine prescriber approval; the full clinical picture does.

In terms of what the evidence shows: SURMOUNT-1, the main phase-3 trial for tirzepatide involving 2,539 adults, reported an average body-weight reduction of around 20 to 21 per cent at the 15 mg dose over 72 weeks. The STEP 1 trial for semaglutide 2.4 mg reported roughly 15 per cent average reduction over 68 weeks. In the more recent SURMOUNT-5 head-to-head trial, published in the New England Journal of Medicine in 2025, tirzepatide produced greater average weight loss than semaglutide 2.4 mg. These are trial-population averages; individual results vary. If you are weighing up which option suits you, our pages on the Mojo weight loss injection and the Mon weight loss injection explain how each is structured, and a broader comparison of the most common weight loss injections available in the UK may also help you decide before looking at cost. For more context on how costs fit into treatment decisions, our honest look at weight loss injection pricing explains what a legitimate price typically covers.

Neither injection is recommended during pregnancy, while breastfeeding, or when actively trying to conceive. They are not licensed for under-18s. Certain medical histories (including a personal or family history of medullary thyroid carcinoma) require specific prescriber discussion before starting. Our clinical team profile, including lead prescriber Mostafa Damghani, gives more detail on who oversees clinical decisions at nume.

If you want to explore whether one of these treatments might suit your situation, start your free consultation and a prescriber will review your answers the same day.