How to read a medication label
A medication or peptide label is a dense little document. This page explains what its fields and numbers represent, so that what you record later reflects what is actually printed in front of you.
Start with the product name
The name is the anchor for everything else on the label, and it usually appears in more than one form: a brand name, and the name of the active ingredient. The same active ingredient can be sold under several brand names, and can appear in products that are otherwise quite different from one another.
Read the ingredient name rather than relying on the brand alone. It is the part that stays constant, and it is the part that official product information is written about.
Strength and concentration are not the same thing
These two words get used loosely in conversation, but on a label they answer different questions.
Strength describes how much active ingredient a product contains. Concentration describes how much active ingredient is present in a given amount of liquid. A tablet has a strength. A liquid in a vial has both a total amount and a concentration, and a label may print either, or both, or express one in terms of the other.
Most confusion when reading a label comes from reading one of these as though it were the other.
What mg and mcg mean
Both are units of mass — they describe an amount of substance, not an amount of liquid.
A milligram (mg) is one thousandth of a gram. A microgram (mcg, sometimes written µg) is one thousandth of a milligram, so 1 mg is the same amount as 1000 mcg.
The two abbreviations look similar in small print and on a curved vial. If a label is hard to read, it is worth being certain which of the two is printed, because they differ by a factor of a thousand.
What mL means
A millilitre (mL) is a unit of volume — an amount of liquid, with no statement about what is dissolved in it.
This is why a volume on its own never tells you how much active ingredient is present. A 2 mL vial describes the size of what is in the container, not its contents.
Total amount and amount per millilitre
A liquid label generally expresses the active ingredient in one of two ways, and the difference matters.
Some labels state an amount per millilitre — a quantity of active ingredient in every millilitre of liquid. Others state a total amount together with a total volume — how much active ingredient is in the container altogether, and how much liquid it is dissolved in.
These are two notations for the same underlying fact, and a label using one is not making a different claim from a label using the other. A label reading “10 mg / 2 mL” and a label reading “5 mg/mL” describe the same amount of active ingredient per millilitre of liquid, written two ways.
Why two similar-looking labels are not interchangeable
Because those two notations exist side by side, labels that lead with the same number can describe different things.
“10 mg/mL” and “10 mg / 2 mL” both begin with 10 mg. They do not describe the same amount of active ingredient per millilitre: the first states an amount in every millilitre, the second states an amount spread across two millilitres.
This is the single most useful habit when reading a liquid medication label: check whether the number you are looking at is per millilitre or in total, before treating it as familiar. Two products from the same category, and even two containers of the same product, can differ here.
Vials and prefilled pens
A vial is a sealed container of liquid that is drawn out separately. A prefilled pen is a device that holds the liquid and delivers it through its own mechanism.
They tend to be labelled differently. A pen's label often speaks in terms of what the device delivers, while a vial's label describes what the container holds. That difference in framing is worth noticing, because it changes what the printed number is counting.
Who made it, and who dispensed it
Labels commonly carry two separate origins: the manufacturer of the product, and the pharmacy or supplier that dispensed it to you. Often a dispensing label is applied over or beside the manufacturer's own.
Where a product has been prepared or repackaged rather than supplied in a manufacturer's finished packaging, the label may be the only record of who prepared it and what they say is in it. If a label carries no identifiable source at all, that absence is itself worth noting — and worth asking your pharmacist or prescriber about.
Lot number and expiry
A lot (or batch) number identifies the production run a container came from. It is the reference used if a manufacturer or regulator issues a notice about a particular batch.
An expiry date is the date up to which the manufacturer supports the product as described on the label. Some labels also carry separate handling information — storage conditions, or how long a product is supported after first use — which is not the same field as the printed expiry date.
What may simply be missing
Not every label carries every field. A dispensing label may omit the manufacturer. A repackaged product may carry no lot number. A concentration may be printed in a notation you have not seen before, or partly obscured by a second label placed over the first.
A missing field is not a value of zero and not a detail to fill in from memory or from a previous container. It is a gap, and the right response to a gap is to ask the pharmacy or prescriber who supplied it.
What pepcil looks for when you scan
pepcil reads the label with your camera and shows you, field by field, what it recognised — the product name, strength, concentration and expiry among them — together with how confident it is in each one. On the default build this runs on-device.
Recognition is a reading, not a verdict. Fields pepcil is unsure about are flagged rather than guessed at, and everything it shows you is presented for you to check against the label in your hand.
When something is missing or unclear
Nothing from a scan is saved on its own. You confirm each field before it becomes part of your record, and if something looks wrong you correct it or leave it blank. A field left blank stays blank — pepcil does not complete it from a previous scan or from a general expectation of what such a label usually says.
Reading and logging are kept separate by design. Information you read in pepcil never transfers a number into your record; what gets logged is only what you entered and confirmed.
What pepcil does not determine
pepcil does not tell you what your dose should be, work out how much to prepare or inject, decide whether a dose is appropriate for you, or judge whether a product is authentic, safe or correctly supplied. It does not diagnose, prescribe, or replace advice from a pharmacist or prescriber.
What it does is help you see what is printed on the label clearly, and keep an accurate record of what you confirmed.