Semaglutide 5mg reconstitution: why no calculator can replace a licensed pen

What the trial data says about semaglutide doses, and why "5mg" doesn't appear

The STEP 1 trial, published in the New England Journal of Medicine, tested once-weekly subcutaneous semaglutide at a 2.4mg maintenance dose in adults with obesity over 68 weeks. Participants who reached and held that dose lost an average of around 15% of body weight. That 2.4mg figure (not 5mg, not any higher unlicensed amount) is the dose the MHRA approved, the dose the trial measured, and the dose Novo Nordisk's engineers calibrated Wegovy pens to deliver.

More recently, on 14 April 2026, the MHRA approved a dedicated single-dose 7.2mg Wegovy pen as the new maximum for eligible adults with a BMI of 30 or above. The titration path leading to it still starts at 0.25mg and steps up approximately every four weeks under prescriber oversight. At no point does the schedule pass through anything close to 5mg. If you've read about a "5mg semaglutide" product online, it refers to a compounded powder preparation sold in some markets without UK regulatory authorisation.

The distinction isn't pedantic. Semaglutide is a large peptide molecule that degrades quickly once it's in solution. The pre-filled Wegovy pen protects the formulation, controls the dose precisely, and has been tested as a complete system, needle, plunger, reservoir and all. Reconstituting a powder introduces variables in bacteriostatic water volume, storage temperature, injection timing and concentration that the licensed product eliminates by design, and if you are curious about what that process actually involves, our detailed walkthrough of reconstituting semaglutide 5mg explains the steps and why they carry meaningful risk. There is no verified calculator that can safely replicate what the pen does, because the pen was built so that no calculation is needed.

Why calculators for reconstituted semaglutide circulate, and what they get wrong

Compounded semaglutide powders have been widely sold, particularly in the United States, where compounding pharmacies filled supply gaps during shortages. That market generated a whole ecosystem of dosing calculators, often expressed in milligrams per millilitre, that look authoritative at a glance. Some of those tools have migrated online and now surface on UK search results, where they have no regulatory standing whatsoever.

The MHRA has seized large quantities of unlicensed weight-loss injections from UK sellers, including counterfeit pens found to contain the wrong substances entirely. A calculator built around an unlicensed powder can't tell you whether the powder in front of you is what it claims to be, whether the concentration is correct, whether sterility has been maintained, or what the actual active semaglutide content is after storage, and our guide to 5mg semaglutide reconstitution sets out exactly why these uncertainties cannot be resolved by dosing tools alone. Those are not gaps a spreadsheet can close.

If you want to understand the licensed dose journey, our guide to Wegovy's dose schedule walks through each step and what to expect at each stage. For questions about how the Wegovy pen works before you reach that schedule, the Wegovy overview page covers the full picture. And if cost is part of what's driving the search (compounded versions can look cheaper) it's worth reading the honest breakdown on the cost of Wegovy in the UK before drawing conclusions.

What legitimate access to semaglutide looks like in the UK

Wegovy is a prescription-only medicine. A prescriber who has reviewed your health history, weight, and any relevant conditions decides whether it's appropriate and at what starting point, and if you have come across references to higher compounded quantities while researching your options, our page on 10mg semaglutide reconstitution explains what that process involves and why it falls outside the licensed framework in the UK. That clinical step isn't a formality, it's the mechanism that keeps dosing safe and catches contraindications before they become problems.

A simple check anyone can do in under a minute: before ordering from any online pharmacy, look up the pharmacy's registration number on the GPhC pharmacy register. If it isn't there, walk away. A registered pharmacy will have a GPhC number displayed on its website; at nume ours is 9012878.

At our pharmacy, a GPhC-registered Independent Prescriber reads every consultation, a real clinician, not automated software. Medicines move through the licensed UK supply chain from Novo Nordisk's authorised distributors. Once approved, treatment is dispatched the same day if you order before noon on a working day, and arrives via tracked DPD delivery the next working day in plain packaging. The pen that arrives is calibrated, sealed, and ready to use, no mixing required, and no room for the errors that reconstitution introduces.

If you'd like to understand whether semaglutide treatment might be appropriate for your situation, the right first step is a clinical conversation rather than a calculator. You can explore your options and check your eligibility with our prescribers at no cost to start.