How to Read a Peptide Vial Label

By Tessaro Pty Ltd, the maker of Pepti · Reviewed October 2026

This page goes through a vial label field by field and says what each one is for in a tracking record. It does not help you choose a product or judge a supplier, and a label cannot tell you what is actually in a vial. It is written by the maker of Pepti, so read the Pepti-specific parts as a description of our own app.

The two numbers people mix up: total amount and strength

Most arithmetic mistakes with vials start with one unasked question: is the number on the label the total amount in the vial, or the amount in each millilitre? They are different kinds of fact.

A vial of freeze-dried powder states a total amount. The US label for tesamorelin for injection, for example, describes a “lyophilized powder in a single-dose vial” and supplies Sterile Water for Injection to mix it with (FDA label, DailyMed). A powder has no concentration until liquid is added. The concentration is created at the moment you mix, and it equals the amount in the vial divided by the volume of liquid you put in.

A vial or pen of solution is already liquid, so its label states a strength per millilitre, usually alongside the volume in the container. The US label for tirzepatide injection, for instance, describes a solution supplied in pens and in “single-dose vials, multi-dose vials” (FDA label, DailyMed). Here the label states the concentration for you.

Put a total amount into a field that expects a strength per millilitre, or the other way round, and every draw volume worked out afterwards is wrong. When you copy the number, copy what kind of number it is.

Units: write them exactly as printed

Labels state amounts in milligrams or in micrograms, and a milligram is one thousand micrograms, so a slip between the two is a thousandfold error. Copy the unit along with the number every time.

The word ‘units’ deserves particular care, because it is used for two unrelated things. On a U-100 syringe, units are marks of volume: one hundred of them to the millilitre. On some labels, international units, written IU, describe the product itself. A unit mark on a syringe and an IU on a label are not the same thing, and this page gives no conversion between them. The free reconstitution calculator on this site turns a volume into syringe units; it does not convert IU.

Lot or batch number

The lot number exists for traceability. FDA inspection guidance requires a finished product to be identified with “a lot, or control number that permits determination of the complete history of the manufacture and control of the batch” (FDA inspection guide).

In your own log the lot number does a smaller version of the same job. It ties every injection you record to one specific vial from one specific batch. If a question is ever raised about a batch, or one vial behaves differently from the last, the lot number is how you find exactly which entries it touched.

Expiry date and storage statement

These two belong together. The FDA describes an expiration date as reflecting “the time period during which the product is known to remain stable, which means it retains its strength, quality, and purity when it is stored according to its labeled storage conditions” (FDA, Expiration Dates: Questions and Answers). The date holds only if the storage statement was followed, so copy both, and copy the storage statement word for word. Our guide to peptide storage and expiry covers how the clock changes once a vial is opened or mixed.

Single-dose or multiple-dose

Labels also say how a container is meant to be used, and the wording differs between products. Sterile Water for Injection is “supplied only in single-dose containers” (product label). Bacteriostatic Water for Injection is “supplied in a multiple-dose container from which repeated withdrawals may be made” (product label). The tesamorelin vial itself is labelled “Single-Dose Vial - Discard Unused Portion”.

Whatever the wording on your own vial is, copy it instead of assuming.

Compounded vials: read the pharmacy’s label

A compounded vial is not an approved product and does not carry an approved product label. The FDA puts it plainly: “a compounded drug is not approved by FDA” (FDA, Compounding and the FDA). Its label comes from the pharmacy that prepared it, and its strength is whatever that pharmacy made it to.

For the record, that has one practical consequence: read the strength from the vial in front of you every time, and never carry a figure over from the previous vial, even from the same pharmacy.

When a label is sparse

Some vials, particularly those sold for research, carry very little: a name, an amount, and not much else. Record what is there, and record what is missing as missing. A note that no lot number or expiry date was printed tells you later that the gap was on the vial, not in your note-taking.

Whether to use a vial with an incomplete label is a question for the source of the material or for whoever directs your care.

What to copy into your log

A photograph of the label, taken before the first use, is a sensible backup.

How Pepti uses what is on the label

When you add a vial in Pepti you enter what the label says. For a powder you enter the amount in the vial and, when you mix it, the volume of water you added, and the date you mixed it; the app does not calculate the concentration, the volume to draw or syringe units. For a solution that arrives ready to use, you enter the strength printed on the label, and there is no mixing step.

Each vial also holds the vendor, the lot or batch number, the expiry date, where it is stored and what it cost. From there Pepti links each injection to the vial and alerts you when its expiry or use-by date is approaching. The free walk-through of what to draw on this site (not part of the app) sets out the arithmetic step by step, and the reconstitution log guide covers what to record at the moment you mix.

The compound reference index lists each compound we cover with its sources, and the glossary defines the terms used here.

Sources (7)

1. US Food and Drug Administration — Inspection guide: Dosage Form Drug Manufacturers cGMPs. fda.gov
2. US Food and Drug Administration — Expiration Dates: Questions and Answers. fda.gov
3. US Food and Drug Administration — Compounding and the FDA: Questions and Answers. fda.gov
4. Tesamorelin for injection — US FDA label, dosage forms, storage and handling. FDA label (DailyMed)
5. Tirzepatide injection — US FDA label, storage and handling. FDA label (DailyMed)
6. Bacteriostatic Water for Injection, USP — US product label. FDA label (DailyMed)
7. Sterile Water for Injection, USP — US product label. FDA label (DailyMed)

Common questions

What is the difference between total amount and strength on a vial?

Total amount is how much of the compound is in the whole vial. Strength is how much is in each millilitre. A vial of powder states a total amount and has no strength until you add liquid; the strength then equals the amount divided by the volume added. A vial or pen of solution states its strength on the label. Log which kind of number you copied, because the arithmetic differs.

Why should I log the lot number?

The lot number ties each injection in your log to one specific vial from one specific batch. FDA inspection guidance requires a finished product to carry a lot or control number that allows the history of the batch to be determined. In your own record it means that if a question comes up about a batch, you can see exactly which entries it touched.

Are the units on a syringe the same as IU on a label?

No. On a U-100 syringe, units are marks of volume, one hundred to the millilitre. IU on a label describes the product itself. They are different things, and Pepti does not convert between them or calculate syringe units at all; it records the figures you enter.

What if my vial has no expiry date or lot number?

Record that none was printed, along with the supplier and the date you received the vial. Do not borrow a date from a different product. Whether to use the vial is a question for the source of the material or for whoever directs your care, not for a tracker.

Does Pepti tell me what dose to take?

No, nowhere, by design. You enter a figure you already have and Pepti records it with the date, time, injection site and vial. It never suggests, recommends, or calculates what that figure should be. That is a decision for you and whoever directs your care, and Pepti stays on the record-keeping side of that line.

Is my data private?

Pepti has no account and no sign-up, and your protocol and health data stay on the device. There is no cloud sync. That data leaves your phone only if you turn on the AI coach or lab-report import, both behind one consent switch, and then only your coach messages with the app context they need, or the report you import, are sent to Pepti's server and processed by Anthropic. With both off, none of it is held on a server for anyone to lose, sell, or hand over.

If you draw from vials and want each one's label details, lot number and dates in one private record on your iPhone, Pepti is built for that. If you keep a paper log or a spreadsheet instead, the fields above are the ones worth copying.

This page describes how to read and record a label. It does not recommend any compound, product or supplier, and it provides no dose figure and no schedule.

Not medical advice. Pepti is a record-keeping tool, not a medical device.

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