How much bacteriostatic water do I add to a 5000 IU HCG vial?

There is no single required amount. A common choice is 2 ml of bacteriostatic water, which makes a 5000 IU vial into 2500 IU per ml. That concentration gives round, easy-to-draw syringe numbers: 250 IU is 10 units, 500 IU is 20 units. You can use 1 ml, 3 ml, or 5 ml instead. More water dilutes the same total 5000 IU across a larger volume, so each dose is more units on the syringe but the same amount of hormone. The vial always contains 5000 IU regardless of how much water you add.

How many units on an insulin syringe is 250 IU or 500 IU of HCG?

It depends entirely on your concentration, which depends on how much water you added. At the common 2500 IU/ml (5000 IU vial plus 2 ml water), 250 IU is 10 units and 500 IU is 20 units on a U-100 insulin syringe. On a U-100 syringe, 1 unit equals 0.01 ml. If you reconstitute with a different water volume, recompute using the mixing chart below or the calculator, because the unit numbers change.

Should I use bacteriostatic water or the diluent supplied with the vial?

Pharmaceutical HCG usually ships with a sterile diluent that is intended for single use with no preservative. Bacteriostatic water contains 0.9% benzyl alcohol, a preservative that inhibits bacterial growth and is generally chosen when a reconstituted vial will be entered multiple times over days or weeks. Many people reconstituting a multi-dose vial prefer bacteriostatic water for that reason. See our guide on bacteriostatic versus sterile water for the trade-offs.

How long does reconstituted HCG last in the fridge?

Once mixed, HCG should be stored at 2 to 8 degrees Celsius (refrigerated), not frozen. Manufacturer labels commonly state reconstituted solution is used within about 30 days, and some allow up to 60 days; check the specific product's instructions. The dry, unreconstituted powder is far more stable. Discard sooner if the solution looks cloudy, discolored, or has particles.

Is HCG dosing for TRT different from fertility dosing?

Yes, and both are prescriber-directed. In a testosterone-replacement context HCG is used off-label at relatively low doses to help preserve testicular function and intratesticular testosterone. Fertility and hypogonadotropic hypogonadism protocols, sometimes combined with other gonadotropins, typically use different and often higher doses. The right dose and schedule is a clinical decision, not something to copy from a chart.

Why is HCG measured in international units instead of milligrams?

HCG is a large glycoprotein hormone standardized by its biological activity rather than its mass, so it is expressed in international units (IU). That is why vials read 5000 IU rather than a milligram figure, and why every reconstitution and dosing calculation for HCG works in IU. Do not try to convert HCG to mg or mcg the way you would a small peptide.

HCG Reconstitution Guide: Mixing 5000 IU and Dosing

What HCG Is and Why It Is Dosed in International Units

Human chorionic gonadotropin (HCG) is a glycoprotein hormone that closely mimics luteinizing hormone (LH). In men it binds the same receptors on testicular Leydig cells that LH would, prompting them to produce testosterone. That single mechanism explains its two main research and clinical uses: preserving testicular function and intratesticular testosterone during testosterone therapy, and restoring sperm production in men with hypogonadotropic hypogonadism.

The first thing to understand before mixing anything is that HCG is measured in international units (IU), not milligrams or micrograms. Small peptides like BPC-157 or the GLP-1 drugs are dosed by mass, so their calculators work in mg and mcg. HCG is a large, complex hormone standardized by biological activity, so a vial reads "5000 IU" rather than a weight. Every calculation on this page stays in IU. Trying to convert HCG into mg is a category error that leads to dosing mistakes, so do not do it.

Note on regulatory status. HCG is a prescription medication. It is FDA-approved for specific indications, and its use to support testosterone therapy is off-label, meaning a licensed prescriber directs it outside the original label. Research-grade material sold "not for human use" is not held to pharmaceutical standards. The figures below are educational and describe how the arithmetic works, not a recommendation to self-treat.

How HCG Works: What the Research Shows

The clearest data point on low-dose HCG comes from a controlled study in healthy men whose natural gonadotropins were suppressed by exogenous testosterone. Adding low-dose HCG every other day maintained intratesticular testosterone within or near the normal range. The 250 IU every-other-day arm kept intratesticular testosterone only about 7% below baseline, and higher doses raised it further (Coviello 2005, J Clin Endocrinol Metab, PMID 15713727). This is the study most often cited for why small HCG doses can preserve testicular activity when LH signaling has been switched off, and it used doses of 125, 250, and 500 IU.

That is the mechanism people are trying to reproduce when HCG is added alongside testosterone: keep the Leydig cells working so the testes do not fully shut down. Whether that is appropriate for any given person, and at what dose, is a clinical question for a prescriber.

HCG Half-Life

HCG clears slowly compared with the short-acting peptides. Its elimination is biphasic, with an initial half-life on the order of 6 to 11 hours and a terminal half-life around 23 to 37 hours, often summarized as roughly 33 hours. That relatively long terminal half-life is why community and research protocols usually dose it a few times a week or every other day rather than daily. The long tail also means levels accumulate somewhat with frequent dosing.

The Reconstitution Math

HCG ships as a freeze-dried (lyophilized) powder that has to be mixed with liquid before it can be drawn into a syringe. The powder holds a fixed total activity, for example 5000 IU. Adding water does not change that total. It only spreads those 5000 IU across whatever volume of water you add, which sets the concentration.

The core relationships are simple:

Concentration (IU per ml) = total IU in the vial ÷ ml of water added.
On a U-100 insulin syringe, 1 unit = 0.01 ml.
Units to draw = desired dose in IU ÷ concentration (IU/ml) × 100.

Take the standard example. A 5000 IU vial plus 2 ml of bacteriostatic water gives 5000 ÷ 2 = 2500 IU/ml. To draw 250 IU: 250 ÷ 2500 × 100 = 10 units. For 500 IU that is 20 units, and for 1000 IU it is 40 units. People like 2 ml precisely because it produces these round numbers.

The amount of water is a choice, not a rule. Using more water makes each dose more units on the syringe (easier to measure accurately for small doses) but a larger injection volume. Using less water concentrates the dose into fewer units. The total hormone per dose is identical either way. Let the HCG reconstitution calculator do the arithmetic for your exact vial size and water volume, and it will return the units to draw directly.

HCG Mixing Chart (5000 IU Vial)

The table shows units to draw on a U-100 insulin syringe for common doses across four water volumes, all from a single 5000 IU vial.

Water added	Concentration	250 IU	500 IU	1000 IU
1 ml	5000 IU/ml	5 units	10 units	20 units
2 ml	2500 IU/ml	10 units	20 units	40 units
3 ml	~1667 IU/ml	15 units	30 units	60 units
5 ml	1000 IU/ml	25 units	50 units	100 units

Reading the chart: pick your water volume down the left, then read across to the dose you want. Note how 250 IU is 5 units at 1 ml but 25 units at 5 ml. Same hormone, different number on the syringe, because the concentration changed. If your vial is a different strength, the calculator will scale all of this for you. For the mechanics of reading a U-100 syringe and choosing a barrel size, see the insulin syringe guide.

How to Reconstitute HCG, Step by Step

The general process mirrors any lyophilized product. This is a description of the standard technique, not medical instruction.

Let the vial and the water reach room temperature and wipe both rubber stoppers with an alcohol swab.
Draw your chosen volume of water into a syringe, commonly 2 ml for a 5000 IU vial.
Inject the water slowly down the inside wall of the vial rather than blasting it directly onto the powder. HCG is delicate, so avoid a hard stream.
Swirl gently, or roll the vial between your palms, until the powder dissolves. Do not shake it. The solution should end up clear.
Label the vial with the concentration and the date you mixed it so you are not guessing later.

Bacteriostatic Water vs the Supplied Diluent

Pharmaceutical HCG often comes packaged with its own sterile diluent, which is preservative-free and intended for a single use. Bacteriostatic water is different: it contains 0.9% benzyl alcohol, a preservative that suppresses bacterial growth and makes a vial more suitable for repeated entry over days or weeks. Because a reconstituted HCG vial is usually a multi-dose vial that you draw from many times, bacteriostatic water is the common choice for that scenario. The full comparison, including when each is appropriate, is in our bacteriostatic vs sterile water guide.

Storage and Shelf Life

The dry powder is stable and is the form manufacturers ship. Once reconstituted, HCG should be kept refrigerated at 2 to 8 degrees Celsius and not frozen, since freezing can damage the glycoprotein. Reconstituted solution is commonly used within about 30 days, and some product labels allow up to 60 days; follow the specific instructions for the product in front of you. Discard any solution that turns cloudy, changes color, or shows particles, and keep it away from light and heat between doses.

Dosing Context: TRT vs Fertility

Two broad use patterns show up in the literature and in clinical practice, and both are prescriber-directed.

In a testosterone-therapy context, HCG is used off-label to help maintain testicular function and intratesticular testosterone while exogenous testosterone suppresses the body's own LH. Doses referenced in research and community protocols are relatively low, often in the range of 250 to 500 IU two to three times weekly or every other day, echoing the doses studied by Coviello 2005. Treat that only as context for the arithmetic, not as a target for yourself.

Fertility and hypogonadotropic hypogonadism protocols aim to actually drive sperm production, sometimes alongside other gonadotropins such as FSH-containing preparations, and can involve different and often higher doses over longer courses. The appropriate regimen depends on the individual, their labs, and their goals, which is exactly why it belongs with a clinician.

Bottom Line

HCG is an LH-analog hormone dosed in international units, so keep every calculation in IU. A 5000 IU vial plus 2 ml of bacteriostatic water is a clean, popular starting point that turns 250 IU into 10 units and 500 IU into 20 units on a U-100 syringe, but any water volume works as long as you recompute the units. Store the reconstituted vial cold, label it, and let the HCG reconstitution calculator handle the math.

This page is educational and is not medical advice. HCG is a prescription drug, and both the decision to use it and the dose belong to a licensed prescriber who knows your situation.

References

Coviello AD, et al. Low-dose human chorionic gonadotropin maintains intratesticular testosterone in normal men with testosterone-induced gonadotropin suppression. J Clin Endocrinol Metab. 2005;90(5):2595-602. PMID 15713727. https://pubmed.ncbi.nlm.nih.gov/15713727/