How to read your prescription
What the abbreviations mean, and the mg-versus-mL distinction that is the one genuine hazard in this category.
Updated 2026-09-18
Before your first injection, spend two minutes on the label. It is the difference between drawing the right amount and guessing.
That part is the difference between your dose in milligrams and the volume you draw in millilitres. They are not the same number, the relationship between them depends on the concentration of your particular vial, and compounded preparations vary in concentration between pharmacies and sometimes between refills. Getting this wrong is the one way to seriously harm yourself with a correctly-dispensed medication.
From milligrams to the mark on the syringe
Your dose is written in milligrams. Your syringe is marked in millilitres or units. The concentration on the vial is the only thing that connects them, and compounded concentrations differ between pharmacies and sometimes between refills. This is the single calculation worth confirming with the pharmacy rather than working out alone — they will do it with you on the phone, free.
Abbreviations you will actually meet
| Abbreviation | Meaning |
|---|---|
| SC, SQ, subcut | Subcutaneous — into the fat under the skin, which is where these injections go |
| IM | Intramuscular — GLP-1s are not given this way |
| q, q week, qwk | Every — "q week" means once weekly |
| mL | Millilitre — a volume, what you draw |
| mg | Milligram — a dose, what you are actually taking |
| mg/mL | The concentration: how many milligrams in each millilitre |
| PRN | As needed — you should not see this on a weekly GLP-1 |
| BUD | Beyond-use date — the compounded equivalent of an expiry date, usually much shorter |
The mg-versus-mL problem, worked through
Your dose is prescribed in milligrams. Your syringe measures millilitres, or units. Converting between them requires the concentration printed on the vial.
An illustration, not your instructions. If a vial reads 10 mg/mL, then 1 mL contains 10 mg. A 5 mg dose would be 0.5 mL. If the pharmacy sends a refill at 20 mg/mL instead, that same 0.5 mL now contains 10 mg — double the dose — even though nothing about your prescription changed.
Worth knowing. Check the concentration on every refill. Compare the mg/mL on a new vial against your last one before you draw anything. If it has changed and nobody told you, stop and contact the provider. Never work out your own volume from a previous vial — confirm it against the concentration in front of you, and ask the pharmacy if there is any doubt at all.
Four checks when the box arrives
- Concentration — the mg/mL, checked against your last vial.
- Beyond-use date — is it long enough to cover this supply?
- Storage — most need refrigeration at roughly 36-46°F (2-8°C). Do not freeze.
- The solution itself — it should be clear and free of visible particles. Cloudy or discoloured means do not use it.
Red flags on a prescription
- No concentration stated anywhere. You cannot dose safely without it.
- No prescriber name, or no way to contact them.
- No pharmacy identified on a compounded preparation.
- Directions in "units" with no explanation of what a unit means on your syringe.
- A quantity that does not match the days supply.
- Anything sold to you without a prescription at all — see how to spot a bad seller.
Read next
- Titration, properly explained
When to step up, when to hold, when to go back down, and why restarting after a gap is the one genuinely dangerous mistake.
- How to spot a bad seller
The FDA sent more than 55 warning letters to online GLP-1 sellers in one day. Here is how to tell a licensed programme from the rest.
- GLP-1s after 50
These drugs work at any age. The risks are not identical at every age, and the muscle and bone question deserves more attention than it usually gets.
- The dose ladder
Why you start low, how fast you climb, and why the price of each rung matters more than people expect.
- Is compounded medication still legal?
Yes, but much more narrowly than in 2024. What changed, and the five questions to ask before you start.
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