GLP-1 First Month Weight Loss: What to Expect (October 2026)

01 · The honest answer

How much weight will you lose in the first month?

Expect a small change, not a dramatic one. The first weeks on 2.5mg are an adjustment phase and losses are usually modest; most measurable progress builds from 5mg onward, month by month.¹

Everyone starts Mounjaro on 2.5mg once a week. This starting dose is about letting your body adjust, not about weight loss itself.¹ For a closer look, see our guide to the first month on Mounjaro and the average weight loss in the first month.

02 · Cost

How much does a GLP-1 cost per month?

A month of treatment means one pen. The Mounjaro pen costs £169.99 per month at the starting dose, and a new customer's first order is £40 less with code FIRST40. Every later order is £25 off the standard price. A Wegovy first pen starts at £99.99 as a first-order price.

Across the UK pharmacies we track, Mounjaro pens range from £143.96 to £339.00 per month depending on dose and provider (checked 10 October 2026). For the full picture, see cost of GLP-1 per month and how much Mounjaro is per month.

03 · What is normal early on

What is normal in the first weeks

Experiences differ widely: some people notice appetite change and early loss in week one, others feel little until a higher dose — both are normal. Early loss includes water weight, so the trend over weeks matters more than any single weigh-in. Mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects and usually settle.¹ Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.

If you lose nothing at first, that does not mean the medicine is failing. Your prescriber reviews your response over time rather than after a few weigh-ins.

04 · How many injections

How many injections per month?

Mounjaro is injected under the skin once a week, on the same day each week. Each KwikPen contains four weekly doses.¹ That means a pen is your supply for a month, and the dose steps up only after at least 4 weeks on each dose, depending on how you respond.

05 · Why results build later

Why results build in later months

In the SURMOUNT-1 trial of 2,539 adults, people taking tirzepatide alongside diet and exercise lost on average 15% of their body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, compared with 3.1% with lifestyle changes alone.² These are trial averages and individual results vary. That was measured over 72 weeks, so think in months, not days.¹

See how much weight loss per month on Mounjaro for what later months can look like.

06 · Avoiding fakes and shortcuts

Beware fakes and dramatic claims

Be wary of anyone promising dramatic weight-loss claims in a month. The MHRA has seized thousands of fake weight-loss pens in the UK, and fake pens have caused hospitalisations — some contained insulin rather than tirzepatide.⁷ Only buy from a pharmacy you can verify on the GPhC register; ours is GPhC 9012878. Genuine treatment always involves a prescription and a clinical consultation.⁷

Our free consultation is reviewed by a GPhC-registered prescriber, and delivery is free next-day tracked.