What Does 20 Units of Semaglutide Actually Mean?

You've seen "20 units" mentioned online, here's what's actually going on

You're researching semaglutide and keep seeing references to units. Perhaps a forum post, a social media reel, or a seller's listing mentioned 20 units as a dose or a quantity. It's a reasonable thing to find confusing, because licensed semaglutide products in the UK don't use that language at all.

Wegovy (the licensed brand for semaglutide in weight management) is dispensed as a pre-filled pen. Each injection is described in milligrams: 0.25 mg, 0.5 mg, 1.0 mg, 1.7 mg, and up to 2.4 mg (or 7.2 mg with the newer single-dose pen approved by the MHRA in April 2026). The word "units" does not appear on any licensed Wegovy packaging, because it isn't relevant to how those products are formulated or measured. The NHS medicines page for semaglutide gives a clear overview of how the licensed products work, and milligrams are the dose unit throughout.

So where does "20 units" come from? It almost always refers to compounded semaglutide, drawn from a multi-use vial and administered with an insulin syringe. Insulin syringes are calibrated in units, which is why that language enters the picture. But the number of units that equals a particular milligram dose depends entirely on how concentrated the vial solution is, and that varies between preparations. Twenty units from a 1 mg/ml vial is a very different dose from 20 units drawn from a 5 mg/ml vial.

That variability is not a minor technical footnote. It is the reason dosing errors with compounded preparations can be serious.

Why compounded semaglutide sits outside the licensed supply chain

A question our prescribers hear most weeks is some version of: "Is the vial version basically the same thing?" The honest answer is no, not in any sense that matters for safety.

Wegovy pens are manufactured to MHRA-approved specifications, with fixed pre-set doses, stability testing, sterility assurance, and labelling that tells you exactly what you are injecting. Compounded semaglutide vials are not covered by any MHRA marketing authorisation for weight management. They are not assessed for quality, potency or sterility by the UK regulator before reaching the patient. The MHRA has warned publicly about unsafe products sold online, including preparations that arrived in patients' hands with no clinical oversight at all, you can report suspected counterfeit or unsafe medicines through the MHRA's Yellow Card scheme.

The risks are not abstract. Incorrect reconstitution, inaccurate measurement and unverified concentration have all been reported in clinical literature as routes to overdose or underdose. For a medicine that works on appetite signalling and gastric emptying, getting the dose wrong in either direction has real consequences.

If you're trying to understand what a legitimate semaglutide treatment looks like, our semaglutide overview covers the licensed products in full, and our Wegovy guide sets out the approved dosing pathway in plain terms. For a grounding in how concentration affects what "units" actually means in practice, the semaglutide ml to units conversion page works through the maths.

What the licensed semaglutide schedule actually looks like

Because this question often comes from people who are trying to work out whether a dose they've seen online corresponds to a stage of legitimate treatment, it's worth being direct about what the real schedule looks like.

Wegovy treatment begins at a low starting dose to let the body adjust, the first four weeks use the lowest available pen. From there, the prescriber moves the dose upward in four-weekly steps, based on how well the treatment is tolerated, until the maintenance level is reached. The maximum approved dose is now 7.2 mg weekly, following the April 2026 MHRA approval of the dedicated single-dose pen for adults with a BMI of 30 or above. That approval is covered in the MHRA's official announcement on GOV.UK.

None of those steps involve drawing up a syringe, converting units, or calculating concentration. The pen handles measurement. That is largely the point.

If you're looking at a number like 20 units and trying to map it onto one of these steps, it can't be done without knowing the preparation's exact concentration, which a licensed product doesn't require you to know. For a practical illustration of how lower doses compare, our page on what 10 units of semaglutide represents walks through the same conversion logic with a different starting figure, and if you want to see how the same logic applies at a nearby reference point, our guide to 12 units of semaglutide covers what that draw actually means depending on vial concentration. The 50 units page covers the higher end of the range people commonly ask about.

Wegovy is a Prescription-Only Medicine. Whether semaglutide is appropriate, which dose to start at, and when to adjust it are decisions that belong to a prescriber who knows your medical history. If you'd like to explore whether Wegovy could be right for you through a proper clinical assessment, you're welcome to speak to our prescribers, the consultation is free, and a named clinician reviews every application the same day.