Weight Loss Injections Dosage: What the Schedule Actually Looks Like

Your first pen arrives and the dose feels surprisingly small

That's intentional. Mounjaro's licensed UK schedule begins at 2.5 mg once weekly. The sole purpose of that starting strength is to let your body adjust to a medicine that slows gastric emptying and changes appetite signalling, jumping straight to a higher dose would make nausea and vomiting much more likely. After four weeks at 2.5 mg, most people move to 5 mg, then 7.5 mg, and so on in four-week steps through the available UK strengths: 2.5, 5, 7.5, 10, 12.5, and 15 mg. The 15 mg dose is the highest licensed strength. Your prescriber decides when each increase is appropriate based on how the previous dose was tolerated, not on a fixed calendar. Some people stay at an intermediate dose because it suits them well. That's a clinical decision, not a setback.

Wegovy follows a similar principle. The semaglutide schedule steps up from 0.25 mg through 0.5 mg, 1.0 mg, 1.7 mg, and 2.4 mg, again with roughly a month at each level. As of April 2026, the MHRA has also approved a 7.2 mg semaglutide single-dose pen for adults with a BMI of 30 or above, reaching that dose via the same gradual titration pathway. The NHS medicine information for tirzepatide covers the full prescribing picture at patient level.

What actually drives the step-up, and what slows it down

The four-week minimum between dose increases is not arbitrary. It reflects how long these medicines take to reach a steady concentration in the body after each change. Pushing faster tends to amplify side effects without meaningfully improving results. The most common side effects across both medicines are gastrointestinal: nausea, loose stools, reflux, and a heavy feeling after eating. These typically ease within a week or two of each dose change as your body adjusts. If they don't, staying at the current dose for longer before stepping up is a standard clinical response.

Some factors that can slow a titration include persistent nausea that hasn't settled, a gap in treatment caused by supply or illness, or a prescriber's assessment that the current dose is already producing good progress. None of this is failure, the schedule is a guide, not a race. Readers sometimes ask about what to expect specifically at the 2.5 mg starting point, which is worth reading before your first pen arrives. For context on how different injectable approaches compare more broadly, the dosage framework for Saxenda (liraglutide, a different GLP-1) follows a daily rather than weekly injection schedule.

Maintenance dose versus maximum dose, not always the same thing

People sometimes assume the goal is always to reach the highest available strength. That's not quite right. The maintenance dose is defined as the highest strength you tolerate well, up to the licensed maximum. For Mounjaro, trial participants who reached 15 mg saw an average body-weight reduction of around 20–21% over 72 weeks in SURMOUNT-1, as published in the New England Journal of Medicine. But clinically meaningful weight loss can occur at lower maintenance doses too. Wegovy's STEP 1 trial reported roughly 15% average weight loss over 68 weeks at the 2.4 mg maintenance dose.

The point is that the dosage schedule is personalised at every stage. What works for one person at 10 mg may not be the right endpoint for someone else. A prescriber looking at your full picture (weight trajectory, side-effect profile, any relevant health conditions) is far better placed to judge that than any general dosage guide. You can read more about the range of licensed weight loss options if you want to understand how Mounjaro and Wegovy sit alongside other approaches before starting a consultation.

Injections that don't treat weight, and why they sometimes cause confusion

A few injectable products circulate online under the broad label of weight loss injections but are not licensed for that purpose in the UK. Vitamin B12 injections, for example, are sometimes promoted in weight-management contexts, the evidence around B12 injection dosage for weight loss is far thinner than for GLP-1 medicines. Similarly, L-carnitine injections have a following in certain fitness communities, but the licensed evidence for L-carnitine as a weight loss injection does not match what exists for tirzepatide or semaglutide. NICE's appraisal of tirzepatide (TA1026) recommends it for adults with a BMI of 35 or above and at least one weight-related condition on NHS pathways, with lower BMI thresholds applying for some ethnic backgrounds under UK guidance. Private routes, like a consultation through a regulated online pharmacy, have different starting criteria per the licensed SmPC, a BMI of 30 or above, or 27 or above with a qualifying condition, and if you want to explore those options you can buy weight loss injections through a regulated online pharmacy after completing a prescriber consultation.

If you're ready to understand which dosage schedule might suit your situation, our prescribers can walk through the options with you. Start your free consultation at our treatment page.