Reader’s guide · First edition · September 2026 · Revised September 15, 2026
Reconstitution, Injection, and Storage
The mechanics of a prescribed peptide, from powder to syringe to sharps bin
Approved peptide drugs mostly arrive in pens that hide the mechanics. Compounded peptides arrive as a vial of powder, a vial of water, and a bag of syringes, and the pharmacy's counseling is often a printed sheet. This guide covers what the sheet leaves out: which water, how much, how to draw a dose, where to inject, how long a mixed vial lasts, and what to do when something goes wrong.
Who this is for
Written for adults who have been prescribed a compounded injectable peptide and dispensed a vial rather than a pen. It describes standard subcutaneous technique as taught by pharmacists and diabetes educators. It is not medical advice, and your pharmacy's label and your prescriber's instructions override anything here.
- The vial
- Lyophilized (freeze-dried) powder or, from some pharmacies, already-mixed solution. The label states the drug, the total milligrams, the lot, and the beyond-use date.
- The diluent
- Bacteriostatic water (0.9% benzyl alcohol) for a multi-dose vial you will draw from for weeks. Sterile water without preservative is for single use only.
- Syringes
- U-100 insulin syringes, 0.3 mL, 0.5 mL, or 1 mL, with a fixed 29 to 31 gauge needle 5/16 inch (8 mm) long. Units on the barrel: 100 units = 1 mL.
- Alcohol swabs
- For the vial stoppers and the skin.
- Sharps container
- A puncture-proof container. A detergent bottle with a screw cap is the accepted household substitute.
- The label
- Concentration after mixing, your dose in milligrams or micrograms and in units, storage, and the pharmacist's phone number. If any of these is missing, call before you start.
Bacteriostatic, not sterile, for multi-dose
Sterile water contains no preservative. A vial reconstituted with it and punctured repeatedly over weeks is a culture medium. Bacteriostatic water's benzyl alcohol suppresses growth between uses. It is not for newborns and not for intravenous use, neither of which applies to a subcutaneous peptide.
Six steps, in order, that take about five minutes. Wash your hands first, and let the powder vial and the water reach room temperature: cold water foams more and draws less accurately.
The concentration you just made
Milligrams in the vial divided by milliliters of water added. A 5 mg vial with 2 mL of water is 2.5 mg/mL, which is 2,500 mcg/mL. A 10 mg vial with 2 mL is 5 mg/mL. Write it down; the calculator in the next section does the arithmetic from your label.
units = (dose ÷ concentration) × 100
Dose and concentration in the same unit. At 2,500 mcg/mL, a 250 mcg dose is 0.1 mL, which is 10 units on a U-100 syringe. At 10 mg/mL, a 2.5 mg dose is 0.25 mL, which is 25 units. A misplaced decimal is a tenfold or thousandfold error; the FDA has logged overdoses of exactly this kind from compounded vials.
Dose calculator
Type what is on your label. The result is the arithmetic, not a dose.
- Concentration
- 5 mg/mL
- 5,000 mcg/mL
- Draw
- 0.05 mL
- On a U-100 syringe
- 5 units
- 0.3 mL syringe
- Doses per vial
- 40
units = (dose ÷ concentration) × 100, with dose and concentration in the same unit. Check the result against the units printed on your pharmacy label; if they differ, call the pharmacist before injecting.
| Vial + water | Concentration | Dose | Draw |
|---|---|---|---|
| 5 mg + 2 mL | 2,500 mcg/mL | 250 mcg | 0.1 mL = 10 units |
| 5 mg + 2 mL | 2,500 mcg/mL | 500 mcg | 0.2 mL = 20 units |
| 10 mg + 1 mL | 10 mg/mL | 2.5 mg | 0.25 mL = 25 units |
| 10 mg + 1 mL | 10 mg/mL | 5 mg | 0.5 mL = 50 units |
| 30 mg + 1.5 mL | 20 mg/mL | 7.5 mg | 0.375 mL = 38 units |
- Swab the stopper. Pull the plunger to the number of units you will inject, drawing air into the syringe.
- Push the needle through the stopper and inject the air into the vial. This keeps pressure neutral and makes drawing easier.
- Invert the vial with the needle in it, keep the needle tip below the liquid, and pull the plunger past your dose.
- Tap the barrel so bubbles rise, then push the plunger to your exact unit mark, expelling the bubbles into the vial.
- Read the unit mark at eye level. If it is wrong, push it back and draw again. Never guess.
- Withdraw the needle. Do not recap by hand; use the one-handed scoop if you must.
| Site | Where exactly | Notes |
|---|---|---|
| Abdomen | A hand's width around the navel, staying two inches away from it | Most consistent absorption; easiest to see |
| Thigh | Front or outer thigh, midway between hip and knee | Good for self-injection while seated |
| Upper arm | Back of the arm, between shoulder and elbow | Usually needs someone else to inject |
Rotate within and between sites so no spot is used twice in a row. Avoid bruises, scars, moles, and skin that is red or hard.
- Swab the site and let it dry. Wet alcohol stings.
- Pinch a fold of skin between thumb and forefinger if you are lean; otherwise a pinch is optional with a short needle.
- Insert the needle at 90 degrees (45 degrees if the fold is thin) in one smooth motion.
- Press the plunger slowly to the end, count to five, and withdraw at the same angle.
- Press with a dry swab if it bleeds. Do not rub.
- Syringe goes into the sharps container, uncapped.
- Weekly drugs: same day each week; the day can move as long as at least three days separate two doses.
- Daily peptides: same time each day, most often bedtime for growth hormone releasers and morning for others, as the prescriber directs.
- Never share a syringe, a needle, or a multi-dose vial with another person.
- Unmixed powder
- As labeled. Most lyophilized peptides keep refrigerated (36 to 46 °F, 2 to 8 °C) for months and frozen for longer; some tolerate room temperature briefly for shipping.
- Mixed vial
- Refrigerated, upright, protected from light. The beyond-use date is set by the pharmacy under USP <797>; 28 days after first puncture is the common default for a preserved multi-dose vial.
- Approved pens
- Refrigerated until first use; then the label allows a period at room temperature (for example 21 days for Zepbound pens, 28 days for Wegovy, 56 days for Ozempic).
- Travel
- An insulated pouch with a cold pack, not touching the vial. Never in checked luggage; never left in a car.
- Discard
- On the beyond-use date, if it is cloudy or discolored, if it froze after mixing, or if it was left warm for longer than the label allows.
Research-chemical vials have no beyond-use date
A pharmacy assigns a beyond-use date from tested stability and its own process controls. A chemical supplier assigns nothing. If you were not dispensed the vial by a pharmacy, no one has any idea how long it stays potent or sterile after mixing, and the 28-day convention is borrowed, not earned.
| Problem | What to do |
|---|---|
| Drew too much before injecting | Push it back into the vial and re-draw. Never inject and "make it up next time." |
| Injected too much | Call the pharmacy or prescriber now, not tomorrow; for a GLP-1 overdose expect prolonged nausea and vomiting, and seek care if you cannot keep fluids down. Poison Control (1-800-222-1222) is available at any hour. |
| Not sure whether you injected | Do not double up. Wait until the next scheduled dose and tell your prescriber. |
| Bubble in the syringe | Small air bubbles under the skin are harmless; the concern is only that the bubble displaced part of the dose. |
| Bleeding or bruising at the site | Normal in small amounts. Rotate away from it. Persistent bruising at every site: mention it. |
| Red, hot, swollen, or painful site after a day | Possible infection. Contact your prescriber the same day. |
| Hives, wheezing, swelling of lips or throat | Emergency. Call 911. |
| Vial dropped, cracked, or left warm | Discard. Call the pharmacy for a replacement rather than risking it. |
The pharmacist's number is on the label
Counseling on how to draw and inject is part of what a licensed pharmacy provides, and the call is free. If the label has no pharmacy, you were not dispensed a medicine, and this guide's advice about who to call has no one to point to.
- How much water per mg?
- There is no fixed ratio. The water volume is chosen so that your dose lands between about 10 and 50 units on the syringe, where it can be read accurately. The pharmacy label states the volume; the printed guides in this catalog each assume one standard volume per vial size. Change the water and you change every unit figure.
- Sterile water instead of bacteriostatic?
- Only for a vial you will empty in one draw. Sterile water has no preservative, and a vial punctured repeatedly over weeks grows bacteria. Bacteriostatic water's 0.9% benzyl alcohol prevents that. It is not for infants and not for intravenous use, neither of which applies here.
- Why not shake?
- Peptides are fragile chains that unfold and clump when agitated, and shaking whips air into the solution. Foam is the visible sign. Swirling or rolling dissolves the powder without either.
- How long does it last after mixing?
- As long as the pharmacy's beyond-use date says, which is set from tested stability under USP <797>; 28 days after first puncture is the common default for a preserved multi-dose vial. Some peptides are shorter: the original tesamorelin kit was mixed daily. A research-chemical vial has no beyond-use date because no one tested it.
- Does it need the refrigerator?
- Yes, once mixed: 36 to 46 °F (2 to 8 °C), upright, in the dark. Take it out to draw a dose and put it back. Do not freeze a mixed vial. Unmixed powder keeps as the label says, usually refrigerated for months.
- What if I added too much or too little water?
- The concentration changed, so the units per dose changed with it. Recalculate from the volume you actually added, write the new concentration on the label, and check it against the pharmacy's figure before the next dose. Too little water makes small doses too small to measure; too much may not fit the vial. If you are unsure what went in, call the pharmacist.
- Room temperature or cold?
- Let both vials warm to room temperature before mixing, which takes about fifteen minutes out of the refrigerator. Cold water foams more and cold liquid draws less accurately. Once mixed, the vial goes back in the cold.
None of this is a reason to obtain a vial
Everything on this page assumes a prescription and a pharmacy label. The technique is the same for a research-chemical vial, and so is the arithmetic, but the label, the beyond-use date, and the pharmacist's phone number are missing, and those are the parts that keep people safe.
References
- 1.American Diabetes Association. Insulin administration: technique and site selection. Diabetes Care, Standards of Care in Diabetes, current edition; and Frid AH, et al. New insulin delivery recommendations (FITTER). Mayo Clin Proc. 2016;91(9):1231-1255.
- 2.Bacteriostatic water for injection, USP. Prescribing information (benzyl alcohol 0.9%; not for use in neonates). Hospira/Pfizer.
- 3.United States Pharmacopeia. General Chapter <797> Pharmaceutical Compounding — Sterile Preparations (beyond-use dating of multiple-dose containers). 2023 revision.
- 4.U.S. Food and Drug Administration. FDA's concerns with unapproved GLP-1 drugs used for weight loss (dosing errors with compounded vials). Updated 2025. https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss
- 5.Centers for Disease Control and Prevention. Safe injection practices; and Safe needle disposal for people who self-inject at home. https://www.cdc.gov/injection-safety/
- 6.Zepbound, Wegovy, and Ozempic prescribing information: storage and in-use periods at room temperature. Eli Lilly and Company; Novo Nordisk. Current revisions.