How much bacteriostatic water to mix with 5 mg of semaglutide?

Most users add 2 mL for a clean 2.5 mg/mL concentration, which makes a 0.25 mg starting dose equal 10 units on a U-100 syringe. 1 mL gives 5 mg/mL and 2.5 mL gives 2 mg/mL; either works, the math just changes.

How much bacteriostatic water to mix with 10 mg of semaglutide?

2 mL gives 5 mg/mL (clean starting-dose math at low units), 4 mL gives 2.5 mg/mL (clean math at higher doses). Pick based on which doses you will spend most of your time at.

Do you shake a semaglutide vial?

No. Shaking creates mechanical stress and foaming that can denature the peptide. Swirl the vial gently in a circular motion or roll it between your palms until the solution is clear.

How to open a semaglutide bottle?

Pop the colored plastic flip-cap off the top with your thumbnail. That exposes the rubber stopper. Swab the stopper with alcohol and puncture it with your syringe needle. The aluminum crimp stays on.

How long does reconstituted semaglutide last?

28 days refrigerated at 36 to 46 degrees Fahrenheit is the conservative standard. Some compounding pharmacies extend to 56 days based on stability data. Always follow the beyond-use date your pharmacy printed on the label.

Can you reconstitute semaglutide with regular sterile water?

Only if you plan to use the entire vial in a single sitting, which is essentially never the case with weekly dosing. Sterile water for injection has no preservative; the vial becomes a bacterial risk after the first puncture. Use bacteriostatic water.

What does a properly reconstituted vial look like?

Clear or very faintly yellow, with no particles, no cloudiness, no floaters. If the solution is milky, brown, or particulate, do not inject it. Contact the pharmacy.

Can I cut semaglutide in half?

Brand semaglutide pens are sealed devices and cannot be split. With a compounded vial, you can draw half the prescribed dose with the syringe, which is just math, not physical splitting. Any dose change should be discussed with the prescriber first.

Is reconstituting semaglutide safe to do at home?

It is the intended use case for compounded semaglutide dispensed in patient-administered vials. Safety depends on aseptic technique, correct math, and following the pharmacy's beyond-use date. The FDA has flagged compounded semaglutide for dosing errors, so technique matters.

What happens if I add too much or too little water?

The vial still contains the same total amount of semaglutide, but the concentration is off. Adding 3 mL when you meant 2 mL to a 5 mg vial gives 1.67 mg/mL instead of 2.5 mg/mL. Recalculate your unit count using the actual concentration before drawing the first dose, or call the pharmacy.

How to Reconstitute Semaglutide

Summary: Compounded semaglutide ships as a lyophilized powder. You add bacteriostatic water, swirl gently, label the vial with concentration and date, and refrigerate. The math is the only step people get wrong.

This content is for informational purposes only and is not medical advice. Always consult a qualified healthcare provider before starting, changing, or stopping any medication.

The short answer: add bacteriostatic water to the lyophilized vial through the rubber stopper, let the stream run down the glass wall, swirl gently for a minute or two until the solution is clear, then label the vial with concentration and date and put it in the fridge. Most people use 2 mL of bacteriostatic water in a 5 mg vial for a clean 2.5 mg/mL concentration, or 2 mL in a 10 mg vial for 5 mg/mL. Brand semaglutide pens (Ozempic, Wegovy) come pre-mixed. You only reconstitute when you have a compounded powder.

Below is the full process, the math, the sterility rules from USP 797, and the specific mistakes that destroy potency.

When reconstitution applies (and when it does not)

Brand semaglutide is shipped ready to inject. Ozempic ships as a pre-filled multi-dose pen at 0.68 mg/mL, 1.36 mg/mL, or 2.27 mg/mL depending on the strength ^[3]. Wegovy ships as single-dose pens already mixed ^[4]. You never add water to either. Trying to reconstitute a brand pen will damage the device and ruin the dose.

Compounded semaglutide is different. A 503A compounding pharmacy or 503B outsourcing facility prepares the active ingredient as a lyophilized (freeze-dried) powder inside a sealed glass vial, because the peptide is far more stable dry than in solution. You receive the vial plus a separate vial of bacteriostatic water. You combine them yourself, decide on the concentration, and dose from the reconstituted solution for the next four weeks.

Supplies, in the order you will reach for them

Gather everything before you uncap the first alcohol swab. Working out of order is how contamination happens.

The compounded semaglutide vial (typically 2 mg, 3 mg, 5 mg, or 10 mg of lyophilized powder)
A vial of bacteriostatic water for injection, USP, containing 0.9% benzyl alcohol
A 3 mL or 5 mL luer-lock syringe with an 18 to 22 gauge needle for transferring the water
U-100 insulin syringes (29 to 31 gauge) for drawing your weekly dose
At least two individually wrapped 70% isopropyl alcohol swabs
A clean, flat surface and good lighting
A permanent marker or label for the vial
A sharps container

Do not substitute. Sterile water for injection lacks a preservative and is single-use; using it in a multi-dose vial turns the vial into a bacterial culture after the first puncture. Saline is the wrong solvent. Tap, distilled, or filtered water are not even in the conversation.

The concentration you choose decides everything else

A 5 mg vial holds 5 mg of semaglutide whether you dissolve it in 1 mL of water or 5 mL of water. The amount of drug is fixed. The concentration, and therefore the volume of every weekly dose, depends entirely on how much water you add.

Vial size	BAC water added	Final concentration	0.25 mg dose	0.5 mg dose	1.0 mg dose	2.4 mg dose
5 mg	1 mL	5 mg/mL	5 units	10 units	20 units	48 units
5 mg	2 mL	2.5 mg/mL	10 units	20 units	40 units	96 units
5 mg	2.5 mL	2 mg/mL	12 to 13 units	25 units	50 units	not feasible
10 mg	2 mL	5 mg/mL	5 units	10 units	20 units	48 units
10 mg	4 mL	2.5 mg/mL	10 units	20 units	40 units	96 units

Units in this table are insulin units on a U-100 syringe, where 100 units equals 1 mL. The formula behind every cell is the same.

concentration (mg/mL) = vial strength (mg) / water added (mL)
units to draw = (dose in mg / concentration) × 100

Worked example. You have a 5 mg vial and you add 2 mL of bacteriostatic water. The concentration is 5 / 2 = 2.5 mg/mL. For a 0.25 mg starting dose, you draw (0.25 / 2.5) × 100 = 10 units. Easy to read on the syringe, easy to repeat next week.

Why most people pick 2 mL into a 5 mg vial

Two reasons. First, 2.5 mg/mL makes every standard semaglutide titration dose land on a clean syringe mark: 10, 20, 40, 48 units. No fractional units to round. Second, the total liquid volume is small enough that the vial does not feel overfilled, but large enough that you are not trying to measure 2.5 units of a 5 mg/mL solution for the 0.25 mg starting dose. Measuring 2.5 units on a syringe whose smallest gradation is 1 unit is asking for a 40% dosing error.

Why some people pick 2 mL into a 10 mg vial

Double the peptide in the same water volume gets you 5 mg/mL, which is the brand pen ratio. Weekly doses fit in low unit counts (5 units for 0.25 mg), and a single vial covers more weeks at higher doses. The trade-off is that low doses become harder to measure precisely because you are drawing such tiny volumes.

Sterility, in the language USP 797 uses

USP General Chapter <797> governs the preparation of compounded sterile preparations and sets the rules pharmacies follow to keep injectable drugs free of microorganisms, endotoxins, and particulates ^[2]. You are not operating a clean room, but several USP 797 principles still apply at the kitchen counter.

Aseptic technique. Hands washed, surfaces clean, swab every stopper with 70% isopropyl alcohol and let it air-dry for at least 10 seconds before puncture. Do not blow on it. Do not wipe it off.
First-air principle. Once a stopper is swabbed, do not let anything pass between it and your needle. Do not touch it with your finger to "check" it.
Beyond-use dating. Once you puncture the bacteriostatic water vial or reconstitute the semaglutide, the clock starts. Most compounding pharmacies print a 28-day beyond-use date for refrigerated reconstituted semaglutide; some go to 56 days based on stability data, but 28 days is the conservative default. Follow the date your pharmacy printed on the label, not a number from a forum.
Single-puncture discipline. Use a fresh needle for every draw. Needles dull within one puncture and a dull needle coring the stopper introduces rubber particles into the solution.

The FDA reinforces this. Compounded drugs do not undergo FDA premarket review for safety, efficacy, or quality, and the agency has flagged that compounded semaglutide has been associated with dosing errors and adverse events partly because of inconsistent reconstitution practices in patient hands ^[1]^[5].

The reconstitution procedure, step by step

Wash your hands with soap for at least 20 seconds and dry on a clean towel.
Set up your workspace. Clean, flat surface. Paper towel down. All supplies within reach.
Bring vials to room temperature if either was cold. Ten to fifteen minutes is enough. Cold solvents dissolve peptide more slowly and create more bubbles.
Swab both rubber stoppers (semaglutide vial and bacteriostatic water vial) with separate alcohol pads. Let them air-dry for 10 to 15 seconds.
Draw the bacteriostatic water. Pull air equal to your target volume into the transfer syringe. Insert into the BAC water vial, inject the air to create positive pressure, invert the vial, draw the exact target volume. Tap out air bubbles and re-draw to the line.
Insert the needle into the semaglutide vial through the swabbed stopper. Tilt the vial so the needle tip touches the inside glass wall above the powder, not pointing down at the cake.
Inject the water slowly down the wall. Take 15 to 20 seconds for 2 mL. Let the water run down the glass and pool around the powder. A high-pressure stream hitting the cake directly can shear the peptide molecule and reduce potency.
Withdraw the syringe and dispose of it in the sharps container.
Swirl gently. Roll the vial between your palms or tilt it slowly in a circle. Continue for one to three minutes until the powder is fully dissolved and the solution is clear. Most vials clear within 90 seconds.
Inspect the solution under a bright light. It should be colorless or very faintly yellow, and free of particles or floaters. Anything cloudy, milky, brown, or particulate is a discard. Call the pharmacy.
Label the vial immediately. Write the reconstitution date, the concentration in mg/mL, and the beyond-use date (28 days from today, unless your pharmacy specified otherwise). Use a permanent marker directly on the vial or on a label that will not peel in the fridge.
Refrigerate at 36 to 46 degrees Fahrenheit (2 to 8 degrees Celsius). Store toward the back of the fridge, away from the door, ideally in the original box to protect from light.

What NOT to do

Most reconstitution failures fall into a short list.

Do not shake the vial. Semaglutide is a 31-amino-acid peptide with a fatty acid side chain. Vigorous shaking creates mechanical stress that can denature the peptide, generate foam that traps active compound, and aggregate the molecule. Swirl, do not shake.
Do not spray the water directly at the powder. Aim for the glass wall. Always.
Do not use sterile water for injection in a multi-dose vial. It has no preservative. Bacterial growth becomes a real risk within hours of the first puncture.
Do not freeze a reconstituted vial. Freeze-thaw cycles damage the peptide. Unreconstituted lyophilized powder can be frozen for long-term storage; reconstituted solution cannot.
Do not skip the label. "I will remember the concentration" is how people inject the wrong dose three weeks later. Label every vial.
Do not reuse needles. A needle is dull after a single puncture and risks contamination.
Do not mix semaglutide with other peptides in the same vial. Different molecules have different pH and stability requirements. Co-mixing degrades both.
Do not cut a compounded semaglutide tablet or vial "in half." There is no such thing as cutting a vial of solution. The phrase usually means "draw half the dose," which is fine if your math is right, but the vial itself is not divisible. Brand pens are not splittable either; they are sealed devices.
Do not exceed the beyond-use date. Past 28 days (or whatever your pharmacy specified), discard the remaining solution even if the vial is half full. Potency and sterility are no longer guaranteed.

How to open a fresh semaglutide vial

The factory cap is a small disk of colored plastic over the aluminum crimp. Pop it off with your thumbnail, which exposes the rubber stopper underneath. You do not remove the aluminum crimp; the stopper is designed to be punctured through. Swab the now-exposed rubber surface with alcohol before any needle goes through it.

If the vial came with no flip-cap and you are looking at bare metal, that is unusual for a compounded product and you should call your pharmacy before puncturing.

Storage in detail

Reconstituted semaglutide lives in the fridge. The temperature window is 36 to 46 degrees Fahrenheit, which is the standard household refrigerator range. Two specific rules.

Stay away from the door shelf. Every time someone opens the fridge, the door zone swings several degrees warmer. The back middle shelf is the most temperature-stable spot in most home fridges.

Stay away from the freezer side. Freezing damages the peptide. Some upper-rear corners of fridges run cold enough to flash-freeze items pushed against the back wall. Leave a couple inches of clearance.

Lyophilized (unreconstituted) powder is more forgiving. It is stable refrigerated for the manufacturer's labeled shelf life, and can be frozen at minus 4 degrees Fahrenheit for 12 to 24 months without degradation. Once you add water, none of that applies anymore.

How long a vial lasts

A 5 mg vial reconstituted at 2.5 mg/mL contains 2 mL of solution. Your weekly dose draws a small fraction of that. The vial life depends entirely on the dose.

Weekly dose	Volume per dose at 2.5 mg/mL	Doses per 5 mg vial	Approximate weeks
0.25 mg	0.10 mL	20	20
0.5 mg	0.20 mL	10	10
1.0 mg	0.40 mL	5	5
2.4 mg	0.96 mL	2	2

The 28-day beyond-use date is the limiting factor at the lower doses. A 5 mg vial at 0.25 mg weekly could theoretically last 20 weeks based on volume, but you must discard the remainder at 28 days regardless. This is why many compounding pharmacies size the vial to roughly match four weeks at the prescribed dose; ask your pharmacist about a smaller vial if you are losing significant peptide to beyond-use dating.

Common questions

How much bacteriostatic water to mix with 5 mg of semaglutide?: Most users add 2 mL for a clean 2.5 mg/mL concentration, which makes a 0.25 mg starting dose equal 10 units on a U-100 syringe. 1 mL gives 5 mg/mL and 2.5 mL gives 2 mg/mL; either works, the math just changes.
How much bacteriostatic water to mix with 10 mg of semaglutide?: 2 mL gives 5 mg/mL (clean starting-dose math at low units), 4 mL gives 2.5 mg/mL (clean math at higher doses). Pick based on which doses you will spend most of your time at.
Do you shake a semaglutide vial?: No. Shaking creates mechanical stress and foaming that can denature the peptide. Swirl the vial gently in a circular motion or roll it between your palms until the solution is clear.
How to open a semaglutide bottle?: Pop the colored plastic flip-cap off the top with your thumbnail. That exposes the rubber stopper. Swab the stopper with alcohol and puncture it with your syringe needle. The aluminum crimp stays on.
How long does reconstituted semaglutide last?: 28 days refrigerated at 36 to 46 degrees Fahrenheit is the conservative standard. Some compounding pharmacies extend to 56 days based on stability data. Always follow the beyond-use date your pharmacy printed on the label.
Can you reconstitute semaglutide with regular sterile water?: Only if you plan to use the entire vial in a single sitting, which is essentially never the case with weekly dosing. Sterile water for injection has no preservative; the vial becomes a bacterial risk after the first puncture. Use bacteriostatic water.
What does a properly reconstituted vial look like?: Clear or very faintly yellow, with no particles, no cloudiness, no floaters. If the solution is milky, brown, or particulate, do not inject it. Contact the pharmacy.
Can I cut semaglutide in half?: Brand semaglutide pens are sealed devices and cannot be split. With a compounded vial, you can draw half the prescribed dose with the syringe, which is just math, not physical splitting. Any dose change should be discussed with the prescriber first.
Is reconstituting semaglutide safe to do at home?: It is the intended use case for compounded semaglutide dispensed in patient-administered vials. Safety depends on aseptic technique, correct math, and following the pharmacy's beyond-use date. The FDA has flagged compounded semaglutide for dosing errors, so technique matters.
What happens if I add too much or too little water?: The vial still contains the same total amount of semaglutide, but the concentration is off. Adding 3 mL when you meant 2 mL to a 5 mg vial gives 1.67 mg/mL instead of 2.5 mg/mL. Recalculate your unit count using the actual concentration before drawing the first dose, or call the pharmacy.

What this page does not cover

This is the reconstitution procedure and the sterility logic behind it. Adjacent topics, like the full semaglutide titration schedule, the specific differences between Ozempic and Wegovy pen mechanics, how to switch between vial strengths mid-protocol, and side effect management during dose escalation, have their own pages on this site. The reconstitution math here applies to every compounded semaglutide vial regardless of dose; only the concentration and unit count change.