Deciding to start a weight-loss injection is a big step. Most people spend weeks reading reviews, comparing prices and wondering what the first few weeks will actually feel like.
This guide follows the first month from start to finish: what happens before your pen arrives, what you should expect to pay, how the 2.5mg dose tends to feel, and the myths about bargain jabs that are worth ignoring.
Before you order: the consultation
Mounjaro (tirzepatide) is a prescription-only medicine, so every legitimate purchase starts with a health assessment. With an online pharmacy, this is usually a short questionnaire that a UK prescriber reviews.
Expect to be asked about:
- Your height, weight and BMI
- Existing medical conditions and past illnesses
- Any medicines you currently take
- Previous weight-loss treatments
Some pharmacies also ask for photo ID or a full-length photo to confirm your weight. It can feel intrusive, but it’s a sign the pharmacy is doing its job properly. If a prescriber has doubts, they may ask follow-up questions or decline the order.
What the first month costs
Your first month uses a single 2.5mg KwikPen, which contains four weekly doses. Because it’s the lowest strength, it’s also the cheapest pen you’ll buy.
Across regulated UK pharmacies, prices for this pen vary. Those offering the Mounjaro 2.5mg currently charge around £125 to £145, often with a new-customer discount on the first order. When you compare quotes, check that the price includes the prescriber’s assessment and delivery, and ask what the 5mg pen will cost in month two.
Budget for the cost rising as your dose increases. Knowing the full price ladder upfront avoids an unwelcome surprise later.
Weeks 1 to 4: what to expect on 2.5mg
The 2.5mg dose isn’t designed to deliver dramatic results. Its job is to let your body get used to the medicine before the dose goes up.
Week 1. You inject once, on the same day each week, into your stomach, thigh or upper arm. The KwikPen is pre-set, so there’s no measuring. Many people notice they feel full sooner.
Weeks 2 and 3. Appetite changes often become more noticeable. Mild nausea, indigestion, constipation or diarrhoea are the most common side effects. Eating smaller meals, eating slowly and avoiding greasy food usually helps.
Week 4. Side effects tend to settle as your body adjusts. This is when your prescriber will check in and decide whether to move you up to 5mg.
If side effects are severe or don’t settle, or you have ongoing stomach pain, contact your pharmacy or GP promptly.
Myths about cheap Mounjaro
“It’s the same drug, so the cheapest seller is always best.” Only if it genuinely is the same drug. Unlicensed sellers on social media and marketplaces have been caught supplying fake or contaminated products. A licensed pen from a registered pharmacy is the only way to know what you’re injecting.
“Research peptides are a cheaper version of the same thing.” They aren’t licensed medicines, aren’t made to pharmaceutical standards and aren’t meant for human use. The MHRA has warned the public against them.
“Skipping the consultation saves time and money.” The consultation checks whether the medicine is safe for you. Any seller that skips it is breaking the law and taking a risk with your health.
“Buying several pens at once is cheaper.” Sometimes marginally, but your dose will almost certainly change after the first month, and pens need to be stored correctly. Buying month by month is usually the smarter choice.
To check a pharmacy is legitimate, search its registration number on the GPhC register.
The takeaway
Your first month on Mounjaro is about settling in, not rapid results. Choose a registered pharmacy with clear, all-inclusive pricing, go in knowing what later doses will cost, and give your body the four weeks it needs at 2.5mg.
A fair price and a genuine, properly prescribed pen go together. If a deal means giving up either one, it isn’t worth taking.
This article is for general information and isn’t medical advice. Mounjaro is a prescription-only medicine and is only suitable if a registered prescriber confirms it’s appropriate for you.
