How to Reconstitute Semaglutide: Step-by-Step Guide + Calculator 2026

This content is for informational and educational purposes only. Peptides discussed on this page are research compounds not approved by the FDA for human use. Always consult a licensed medical professional before using any peptide or supplement.

If you have a vial of compounded semaglutide on your desk and aren't sure what to do next, you're in the right place. Reconstituting semaglutide is a straightforward process — but getting it wrong can degrade the peptide or lead to inaccurate dosing. This guide walks you through every step, explains the math behind concentrations, and highlights the mistakes that trip people up most.

Before you mix anything, bookmark the PeptideDeck Reconstitution Calculator — it eliminates the mental math and tells you exactly how many insulin units to draw for any dose.

Quick Answer: Add 2mL of bacteriostatic water to a 5mg semaglutide vial for a concentration of 2.5mg/mL. For a 0.25mg starting dose, draw 10 insulin units (IU) on a U-100 syringe. Inject the water slowly down the vial wall and swirl gently — never shake.

What Is Reconstitution and Why Does It Matter?

Reconstitution means dissolving a lyophilized (freeze-dried) peptide powder in a liquid solvent — in this case, bacteriostatic water (BAC water) — to create an injectable solution. Compounded semaglutide arrives as a dry powder or lyophilized cake because the peptide is far more stable in this form during shipping and storage.

Unlike pre-filled brand-name pens (Ozempic, Wegovy), compounded semaglutide gives you control over your concentration. That means you decide how many milligrams per milliliter end up in the vial, which then determines how many insulin units you draw per dose. Getting this right is non-negotiable — a 2× concentration error is a 2× dosing error.

The good news: the process takes about five minutes, requires no special skills, and the reconstitution calculator handles all the arithmetic for you.

What You'll Need: Complete Supplies List

Gather everything before you start. Working methodically with all supplies on the same clean surface prevents contamination and mid-step scrambling.

Required Supplies

• Semaglutide vial — your compounded peptide (typically 5mg or 10mg)
• Bacteriostatic water (BAC water) — 30mL multi-dose vial is ideal; do not use sterile water for injection (single-use only), saline, or tap water
• Insulin syringes (U-100) — 0.5mL or 1mL capacity; 29–31 gauge needle for injecting
• Drawing syringe — a 3mL or 5mL luer-lock syringe makes it easier to transfer the larger BAC water volume
• Alcohol swabs — at least two (one per vial stopper)
• Clean flat surface — a paper towel or prep pad works well
• Vial labels or permanent marker — to record the reconstitution date and concentration

Optional but Recommended

• Sharps container for safe needle disposal
• Good lighting (helps confirm the solution is clear after mixing)
• Refrigerator thermometer (confirms your fridge is between 36–46°F / 2–8°C)

⚠️ Do NOT use: Regular sterile water for injection (no preservative — single puncture only), bacteriostatic saline (wrong solvent), or any solution that appears cloudy or discolored before mixing.

Semaglutide Concentration Reference Table

The table below covers the two most common vial sizes with the most practical BAC water volumes. Use the PeptideDeck Reconstitution Calculator for vial sizes, doses, or water volumes not shown here.

Vial Size	BAC Water Added	Concentration	0.25mg Dose	0.5mg Dose	1mg Dose	2mg Dose
5mg	1mL	5mg/mL	5 IU	10 IU	20 IU	40 IU
5mg	2mL	2.5mg/mL	10 IU	20 IU	40 IU	80 IU
10mg	1mL	10mg/mL	2.5 IU	5 IU	10 IU	20 IU
10mg	2mL	5mg/mL	5 IU	10 IU	20 IU	40 IU

IU = insulin units on a U-100 syringe (100 IU = 1.0mL). Tip: 2mL into a 5mg vial is the most popular choice because small volumes like 5 IU or 10 IU are easy to measure accurately on a U-100 syringe.

Not seeing your exact setup? The Reconstitution Calculator accepts any vial size, any water volume, and any target dose — and outputs the exact IU to draw.

Step-by-Step: How to Reconstitute Semaglutide

1. Prepare your workspace
   Wash your hands thoroughly with soap for at least 20 seconds. Lay a clean paper towel on a flat surface. Set out all supplies. If your semaglutide vial or BAC water was refrigerated, allow both to reach room temperature for 10–15 minutes — cold solvents mix less readily.
2. Swab both vial stoppers
   Use a fresh alcohol swab on the rubber stopper of the semaglutide vial and a separate swab on the BAC water vial. Allow both to air-dry for 10–15 seconds before touching them with a needle. Skipping this step is one of the fastest ways to introduce contamination.
3. Draw the correct volume of BAC water
   Using your drawing syringe, pull back the plunger to load air equal to the amount of BAC water you need (e.g., pull to the 2mL mark). Insert the needle into the BAC water vial and push the air in — this creates positive pressure that makes drawing easier. Then invert the vial and draw your target volume of BAC water (e.g., 2mL for a 5mg vial at 2.5mg/mL concentration).
4. Inject the BAC water slowly down the vial wall — this is the critical step
   Insert the needle into the semaglutide vial. Tilt the vial at an angle so the needle tip points toward the glass wall rather than directly at the peptide powder. Depress the plunger very slowly — over 20–30 seconds — letting the liquid run down the inner wall and pool at the bottom. Direct high-pressure jets at the powder can shear the peptide and reduce potency. Slow and steady is the rule here.
5. Gently swirl to dissolve — do not shake
   Once all the BAC water is in the vial, remove the syringe and slowly roll the vial between your palms in a circular motion. Semaglutide dissolves readily; most vials are fully clear within 1–3 minutes. If the solution is still cloudy after 10 minutes of gentle swirling, stop — contact your supplier. A properly reconstituted semaglutide solution is clear and colorless (or very faintly yellow), not white or milky.
6. Inspect the solution
   Hold the vial up to a light source and examine it. You're looking for a clear, particle-free solution. Visible floaters, a milky appearance, or unusual color are all red flags. Do not use a solution that doesn't look right.
7. Label the vial immediately
   Write the following on a label or directly on the vial with a marker: reconstitution date, concentration (e.g., "2.5mg/mL"), and expiration date (28 days from today if refrigerated). This takes 30 seconds and prevents potentially dangerous mix-ups later.
8. Store in the refrigerator right away
   Cap the vial and place it in the refrigerator at 36–46°F (2–8°C). Do not leave it at room temperature. See the storage section below for full guidance.

Storage Guide: Keeping Your Reconstituted Semaglutide Potent

Peptide stability after reconstitution depends heavily on temperature, light exposure, and how often the vial is handled. Follow these guidelines to preserve potency through the last dose.

Refrigerated (recommended)

• Temperature: 36–46°F (2–8°C) — standard refrigerator setting
• Shelf life: Up to 28 days after reconstitution
• Storage tip: Keep toward the back of the fridge, away from the door (temperature fluctuates most near the door)
• Light: Store in the dark — the original vial box or an opaque case works well

Frozen (lyophilized powder only)

• Unreconstituted powder can be frozen at -4°F (-20°C) for up to 12–24 months
• Do not freeze reconstituted semaglutide — freeze-thaw cycles damage the peptide structure

Room temperature

• Acceptable for brief transport (<24 hours) but not for ongoing storage
• If your vial has been above 77°F (25°C) for more than a day, discard it

28-day rule: Once reconstituted with BAC water, use within 28 days. Write the expiration date on the label the moment you mix it — no exceptions.

Common Mistakes to Avoid

These are the errors that come up repeatedly, and most of them are easy to prevent once you know to watch for them.

• Shaking the vial. The number one mistake. Vigorous shaking creates bubbles and mechanical stress that can denature the peptide. Always swirl gently.
• Injecting BAC water directly at the powder. Aiming the stream at the powder rather than the glass wall degrades potency. Tilt the vial and let water run down the side.
• Using the wrong solvent. Regular sterile water for injection has no preservative and becomes a bacterial risk after the first puncture. Only use bacteriostatic water with benzyl alcohol for multi-dose vials.
• Skipping the label. "I'll remember" is how people inject twice the dose a week later. Label every vial with concentration and expiration date before it goes in the fridge.
• Miscalculating the dose volume. A 5mg/mL concentration requires 5× less volume than a 1mg/mL concentration for the same dose. Always double-check with the reconstitution calculator before drawing.
• Storing near the fridge door. The door zone sees the most temperature variation every time the fridge opens. Peptides prefer stable, cold conditions — store toward the back.
• Reconstituting too far in advance. Only mix what you'll use within 28 days. Keep unused lyophilized powder frozen until you need it.
• Reusing needles. Needles dull rapidly and become a contamination risk. Use a fresh needle for every draw.

Dosing After Reconstitution

Once your vial is reconstituted and labeled, you're ready to dose. The volume you draw depends entirely on your concentration and target dose. This is where many people second-guess themselves — the Reconstitution Calculator removes all uncertainty.

For a deeper look at starting doses, escalation schedules, and clinical context, see the Semaglutide Dosing Guide. The standard approach starts at 0.25mg weekly for 4 weeks before stepping up — giving your body time to adapt and minimizing GI side effects.

Semaglutide is typically injected subcutaneously (just under the skin) in the abdomen, thigh, or upper arm. Rotate injection sites weekly to avoid lipohypertrophy.

Frequently Asked Questions

How much BAC water should I add to a 5mg semaglutide vial?

2mL is the most common choice, giving a clean 2.5mg/mL concentration. This makes dose math straightforward — a 0.25mg dose is 10 IU, 0.5mg is 20 IU, 1mg is 40 IU. Some people prefer 1mL (5mg/mL) for higher-dose protocols since smaller volumes are easier to inject. Use the reconstitution calculator to verify your specific numbers.

Can I use sterile water instead of bacteriostatic water?

Only if you plan to use the entire vial in a single dose immediately after mixing, which is almost never the case with semaglutide. Bacteriostatic water contains 0.9% benzyl alcohol as a preservative, making it safe for multi-dose vials over 28 days. Sterile water for injection has no preservative and becomes a bacterial contamination risk after the first puncture. Always use BAC water for compounded semaglutide.

My solution looks slightly yellow — is that okay?

A faint, pale yellow tint is normal and acceptable for semaglutide solutions. What you don't want to see: bright yellow, orange, brown, or any cloudy/milky appearance. Visible particulates are also a discard sign. When in doubt, contact your supplier.

How long does reconstituted semaglutide last?

28 days when stored at 36–46°F (2–8°C) in the refrigerator. After that point, discard the remaining solution even if there appears to be peptide left — potency and sterility cannot be guaranteed beyond 28 days. Unreconstituted lyophilized powder can be frozen for much longer (12–24 months at -20°C).

What if the powder doesn't dissolve completely?

Continue gently swirling for up to 10 minutes. Ensure the BAC water was at room temperature before mixing. If the solution remains cloudy or particulate after 10 minutes, do not use it — contact your supplier, as this may indicate a quality issue with the batch.

Can I mix semaglutide with another peptide in the same vial?

This is generally not recommended without explicit guidance from a medical professional. Different peptides have different pH and stability requirements. Mixing compounds increases the risk of degradation, precipitation, and inaccurate dosing.

Do I need to remove air bubbles from the syringe?

Small air bubbles in a subcutaneous syringe are not dangerous (unlike IV injections), but they do displace volume and affect dose accuracy. Tap the syringe and gently depress the plunger to expel visible bubbles before injecting.

Where can I learn about semaglutide dosing protocols?

The Semaglutide Dosing Guide covers starting doses, escalation schedules, maintenance dosing, and what to do if you miss a dose. For compound-specific information including mechanism, half-life, and comparisons to branded GLP-1 medications, see the full semaglutide compound page.