Semaglutide Dosing in Units: What the Numbers Mean for UK Patients

Step 1: Understand what "units" actually refers to here

Most people asking about semaglutide dosing in units have encountered either a social-media post, an unlicensed compound pharmacy listing, or a forum thread where doses are given as "10 units", "20 units" and so on. That language comes from insulin syringes, which are calibrated on a U-100 scale, 100 units per millilitre. Insulin is measured this way because its concentration is standardised. Semaglutide is not.

Licensed Wegovy pens deliver a fixed milligram dose per injection: the pen handles the measurement for you. There is no syringe to load, no unit scale to read. The prescriber sets the dose in milligrams; the pen delivers it. That is the entire interaction the patient needs to have with the dose.

Compounded semaglutide preparations, by contrast, come as a vial of solution at a stated concentration (for example 2 mg/mL or 5 mg/mL) which the patient or carer draws into a syringe. Because syringes read in units or millilitres, people translate the milligram target into those markings. The problem is that the translation changes completely depending on concentration. Our guide to converting semaglutide from mL to units walks through why the same unit reading means a very different milligram dose across different vials.

This is not a maths problem with a neat universal answer. It is a clinical safety issue, and the calculation must be verified by the prescriber or pharmacist supplying the specific product.

Step 2: Trace the licensed milligram schedule and what it represents

For Wegovy (the licensed injectable semaglutide for weight management in the UK), the dose ladder runs 0.25 mg weekly for the first four weeks, then 0.5 mg, then 1.0 mg, then 1.7 mg, and finally 2.4 mg as the standard maintenance dose. In January 2026 the MHRA approved an additional 7.2 mg maintenance option, with a dedicated single-dose pen approved in April 2026. Every step up is made by the prescriber based on tolerability and response, not by the patient independently deciding to increase.

One misconception worth clearing up gently: some people assume the starting dose of 0.25 mg is just a weaker therapeutic dose that they should push through quickly. It isn't. The 0.25 mg step exists because nausea and other gastrointestinal effects are more manageable when the body adjusts gradually, the schedule is designed around side-effect reduction as much as efficacy. Rushing it doesn't improve results; it tends to worsen tolerability.

The full semaglutide dosing guide on our site covers each stage of the schedule in plain terms. The NICE appraisal of semaglutide for weight management, TA875, gives the clinical context behind how these thresholds were assessed.

Step 3: Know the specific risks when doses are expressed in units

The practical risk is straightforward. If a patient is told to draw "10 units" of semaglutide from a vial, and the vial's concentration is 2 mg/mL, they would be drawing 0.1 mL, which at that concentration delivers 0.2 mg. Swap that vial for one at 5 mg/mL, keep the same instruction, and the same 0.1 mL now delivers 0.5 mg, two and a half times the intended dose. Both are still labelled "10 units" on an insulin syringe. That gap is large enough to cause genuine harm. If you are trying to understand what 100 units of semaglutide actually equates to in milligrams, the answer depends entirely on the concentration of the vial you are drawing from.

The MHRA has documented serious adverse events (including hospitalisations) linked to unlicensed semaglutide products. Counterfeit and unregulated preparations have also entered the UK market; the agency's ongoing enforcement has resulted in significant seizures of fake weight-loss pens. A broader overview of semaglutide in the UK covers the supply-chain safety points in more depth.

If you are currently using a preparation described in units and you are not certain of its concentration, do not try to calculate the dose yourself. Contact the prescriber or pharmacist who supplied it. If you cannot reach them, or if the product arrived without proper prescriber oversight, report it via the MHRA Yellow Card scheme.

Step 4: What to do if you want licensed semaglutide treatment

The licensed route in the UK is through a prescriber who assesses your suitability and, if appropriate, issues a prescription for Wegovy at the correct starting dose. The pen does the measurement; you never handle a syringe or convert units. A dosing chart that maps the unit-to-mg question more precisely is available if you need to understand how the figures relate, but for anyone starting treatment from scratch, the milligram schedule on a licensed pen is the right frame of reference.

Our Wegovy treatment page explains the full eligibility picture: adults with a BMI of 30 or above, or 27 and above with a relevant weight-related condition, may be suitable, subject to a clinical assessment. Semaglutide is a prescription-only medicine, and a prescriber makes that determination, not a checklist. For anyone considering treatment, the sensible first step is a consultation with a qualified clinician rather than sourcing a product and working out the dosing independently.

If you'd like to explore whether Wegovy is appropriate for you, you can start a free consultation with our prescribers, a real clinician reviews your details the same day.