How to choose a weight-loss injection: a 5-question framework

Ask ten people which weight-loss injection is best and you'll get ten confident answers — usually the one that worked for them. A more reliable route is to take the decision in order: five questions covering eligibility, goal, health history, routine and true ongoing cost.

The field in July 2026 is three licensed options: Mounjaro (tirzepatide), Wegovy (semaglutide) and — new this summer — the needle-free Wegovy pill (oral semaglutide). Every price below comes from our tracker of 24 regulated UK providers, last checked 4 July 2026.

The three options at a glance

Cheapest four-weekly prices among our 24 tracked regulated UK providers, last checked 4 July 2026. Trial percentages come from different studies and durations — treat cross-trial comparisons as a guide only.

Question 1: do you meet the eligibility bar?

This question settles everything else. UK prescribers work to the licensed thresholds: a BMI of 30 or above, or 27+ with at least one weight-related condition such as high blood pressure — the criteria behind NICE's Mounjaro recommendation (TA1026), applied across all three treatments privately.

Some circumstances close the door regardless of BMI: pregnancy, planning pregnancy, breastfeeding or being under 18 — and a history of pancreatitis or severe gut disease calls for prescriber caution.

Below the thresholds, no regulated UK provider should prescribe any of them — and a seller who would is one to avoid; unregulated and "compounded" products are not licensed in the UK.

Question 2: which weight-loss injection matches your goal?

Be specific about your target — the trial evidence separates cleanly. If you need substantial loss — a fifth of your body weight or more — Mounjaro is the only option that has averaged it: 21.4% at 10 mg and 22.5% at 15 mg over 72 weeks in SURMOUNT-1, and roughly 20% versus about 14% for Wegovy in the SURMOUNT-5 head-to-head.

If your target is more moderate — say 10–15% — Wegovy's STEP 1 average of about 15% at 2.4 mg covers it for many people, at a lower entry cost. The Wegovy pill averaged about 13.6% at 25 mg in OASIS 4 (around 16.6% among consistent takers), close behind the jab it's based on. Our ranking of the best weight-loss injections in the UK unpacks the trade-offs.

Question 3: what does your health history say?

Here a preference can turn into a pointer. If you have existing heart disease, Wegovy holds evidence the others don't: the SELECT trial showed it cut heart-attack and stroke risk in people with cardiovascular disease — proof no rival has. Raise it in your consultation.

Day-to-day side effects won't separate the options much: nausea, diarrhoea, constipation and vomiting run across the whole class, usually worst around dose increases. Our side-effect comparison lines up the finer differences, alongside drug-specific flags — extra caution with diabetic eye disease on tirzepatide; Wegovy not used in type 1 diabetes.

Whatever you shortlist, declare every condition and medicine on the consultation form — the prescriber can only catch what they can see.

Question 4: can you live with the routine?

A treatment you abandon in week six delivers 0% weight loss, whatever the trials say. Both injections are once weekly via a pre-filled pen — easy to fold into the same slot each week.

The pill removes needles but adds discipline: a tablet each morning on an empty stomach with a small sip of water, then a 30-minute wait before food, other drinks or other medicines. Chaotic mornings make that harder than a weekly jab.

Factor in the climb, too: Mounjaro spends four weeks at its 2.5 mg starter dose before stepping up, Wegovy takes around 16 weeks to reach 2.4 mg, the pill roughly 12 weeks to reach 25 mg. For a feature-by-feature breakdown, see how Mounjaro, Wegovy and the rest actually differ.

Question 5: can you afford month six — not just month one?

First-month offers are loud; maintenance prices are what you'll live with. At the ongoing doses, the cheapest tracked prices per four weeks are £174.99 for Wegovy 2.4 mg, £190 for the pill's 25 mg, and £173.99 to £288.99 for Mounjaro depending on whether your maintenance dose lands at 5, 10 or 15 mg.

Then compare providers, because the identical dose varies enormously: Wegovy 2.4 mg spans £174.99 to £249 a month across our 24 tracked providers, Mounjaro 15 mg spans £288.99 to £359, and at Wegovy's 1 mg step the gap reaches £90 a month for the same pen. Our full price comparison works through every dose, and the price tables on our homepage are re-checked regularly — always confirm the current figure on the provider's own site.

Putting the five answers together

Most readers land in one of four lanes:

• You need the largest loss and the budget stretches: ask about Mounjaro — no rival matches its trial averages.
• Heart disease is in the picture: discuss Wegovy first; SELECT gives it evidence the others lack.
• You can't face needles but can keep a strict morning routine: the Wegovy pill — though only 2 of our 24 tracked providers stock it so far.
• Budget leads: compare maintenance-dose prices across providers before comparing drugs — the £70–£90 monthly provider spread is often wider than the gap between medicines.

Hold the framework loosely: these are prescription-only medicines with real side effects, and a good clinician will sometimes redirect you to the option that fits — and that final say is a safeguard.

Frequently asked questions