Bacteriostatic Water for HCG: What the Novarel and Pregnyl Labels Say

1. The Short Answer

FDA-approved HCG (human chorionic gonadotropin) powders come packaged with their own benzyl alcohol-preserved diluent, so the question of which bacteriostatic water for HCG is answered inside the box. Novarel ships with Bacteriostatic Water for Injection, USP, and its label allows 30 days refrigerated after mixing.¹ Pregnyl ships with a benzyl alcohol-preserved saline solvent and allows 60 days.²

HCG is a prescription drug. This page reports what the FDA labels say about diluents and storage. It does not cover dosing, and it is not a substitute for the label or the prescriber.

2. Bacteriostatic Water for HCG: What Four FDA Labels Specify

The pages that rank for this search are mostly mixing charts built around a generic “add bac water” step. None of the ones we checked in September 2026 compared the approved products' own labels, so this section does. We read the FDA prescribing information for three urinary-derived HCG products and one recombinant product and recorded, for each, the supplied diluent, the storage before mixing and the in-use period after mixing. The differences are small on paper and matter in practice.

Novarel and Pregnyl are labeled for intramuscular use; Ovidrel is labeled for subcutaneous use. Check the current label for your product; labels are revised.

3. Three Details the Mixing Charts Get Wrong

Pregnyl's solvent is preserved saline, not plain bacteriostatic water

Most guides say HCG is “mixed with bac water.” For Pregnyl that is not quite true. Its 10 mL solvent vial contains Water for Injection with 0.56% sodium chloride and 0.9% benzyl alcohol, and it carries its own “not for use in newborns” warning.² The preservative is the same as standard Bacteriostatic Water for Injection (0.9% benzyl alcohol),⁵ but the solvent also contains salt. The label does not describe the two as interchangeable.

The in-use period is 30 or 60 days, not 28

The familiar 28-day rule is the default for a punctured multiple-dose vial when the manufacturer gives no other date.⁶ HCG labels give their own date. Novarel says to refrigerate the reconstituted product and use it within 30 days.¹ Pregnyl and the generic Chorionic Gonadotropin for Injection, USP allow 60 days refrigerated.²³ The manufacturer's number takes precedence over the general rule; more on how the two interact in our 28-day puncture rule guide.

The volume is set by the label

The generic Chorionic Gonadotropin for Injection, USP label describes transferring 10 mL of diluent into the 10,000-unit vial and agitating gently until the powder dissolves.³ That gives a concentration of 1,000 USP units per mL. Pregnyl's kit pairs its 10,000-unit vial with a 10 mL solvent vial.² Novarel's label is the one that lists two volumes: 1 mL when the whole vial is given at once, or 10 mL for multiple-dose use with the vial refrigerated between doses.¹ Charts that suggest some other volume change the concentration the label and the prescription are written around. How much of that solution any person uses is a prescribing decision, not something a chart can supply.

4. HCG and Sterile Water

“HCG sterile water” is a common search, usually from people whose kit is missing its diluent or who have heard sterile water is “purer.” Both are reasonable questions, and the labels answer them:

• None of the three urinary HCG labels above supply sterile water. Each supplies a benzyl alcohol-preserved diluent.¹²³
• Sterile Water for Injection has no preservative. It is intended for single use. Pregnyl and the generic product are sold as multiple-dose vials, and a multiple-dose vial is drawn from repeatedly over weeks. Without a preservative, nothing limits growth of bacteria carried in on each needle entry.
• The newborn warning is not relevant to most HCG patients, but it is the reason preservative-free diluents exist. Benzyl alcohol in flush solutions and diluents was linked to neonatal deaths reported in 1982.⁷

If a diluent vial is lost or broken, the pharmacy that dispensed the HCG can replace it or advise on an equivalent. That is a better answer than improvising. For a fuller comparison of the two waters, see bacteriostatic water vs sterile water.

5. Mixing HCG and Bacteriostatic Water: What the Label Covers

The generic label's instructions are short: withdraw air from the powder vial and inject it into the diluent vial, withdraw 10 mL of diluent, add it to the powder vial, and agitate gently until the solution is complete.³ Beyond that, standard aseptic handling applies: a new sterile needle and syringe for every entry, and wiping the stopper with alcohol before each puncture. Our reconstitution technique guide covers the general method; for a dispensed product, the instructions in the carton come first.

After mixing:

• Refrigerate at 2 to 8°C (36 to 46°F).
• Write the mixing date on the vial and count forward 30 or 60 days, depending on the product.
• Do not freeze. Pregnyl's label says so explicitly.²
• Discard at the label's limit even if solution remains.

6. Ovidrel: The Product With Nothing to Mix

Ovidrel is choriogonadotropin alfa, a recombinant HCG. It is supplied as a sterile liquid in a prefilled syringe that delivers 250 mcg in 0.5 mL for subcutaneous injection.⁴ There is no diluent to choose. Recombinant and urinary HCG are dosed on different scales (micrograms versus USP units), so one is not a direct swap for the other without a prescriber's decision.

7. Compounded HCG After March 2020

HCG was historically approved as a drug under the Federal Food, Drug, and Cosmetic Act. Under the Biologics Price Competition and Innovation Act, approved applications for certain biological products were deemed biologics licenses on March 23, 2020. FDA's notice to compounders explains that products that made this transition are no longer eligible for the compounding exemptions in sections 503A and 503B.⁸ FDA correspondence for Pregnyl confirms that its application was converted to a biologics license on that date.⁹

The practical effect is that the compounding exemptions no longer cover HCG, which makes the FDA-licensed products in the table above, each with its own supplied diluent, the reference point for how HCG is mixed and stored.

FDA on HCG sold for weight loss

FDA is also clear about one use: there are no FDA-approved HCG products for weight loss, and HCG products sold over the counter as “homeopathic” are illegally marketed.¹⁰ The agency's consumer update goes further: HCG “is not approved for use without a prescription for any purpose,” and the weight-loss products it warns about are sold as drops, pellets and sprays online, at weight loss clinics and in some retail stores.¹¹ The FDA official quoted in that update put the evidence this way:

FDA also reports receiving serious adverse event reports tied to HCG injections used for weight loss, including pulmonary embolism, cardiac arrest and death.¹⁰ For a diluent guide, the practical point is simple: the labels in section 2 describe a prescription product mixed and stored under a prescriber's direction, and nothing else.

8. Before You Mix: What to Check on the Carton

HCG kits are simple, but a few details are worth confirming before the first puncture, because they decide the storage clock that follows:

• Both vials are present and match. The powder vial and the diluent vial come as a pair. The diluent in a Pregnyl kit is not the same liquid as the diluent in a Novarel kit.
• The powder was stored as labeled. Room temperature before mixing for the three urinary products above, within the ranges in the table.
• The expiration dates are in range. Check both vials. The mixed product's 30 or 60 days does not extend past the date printed on the kit.
• The flip caps are intact. A missing cap on a new vial is a reason to return it, not to mix it.
• You know which in-use period applies. Write the mixing date and the discard date on the vial label as soon as it is mixed.

Storage rules for the diluent itself, before and after it is opened, are covered in our bacteriostatic water storage guide.

9. Where Generic Bacteriostatic Water Fits

Standard Bacteriostatic Water for Injection, USP matches the diluent described on the Novarel label: sterile water with 0.9% benzyl alcohol. It is itself an Rx-only product, approved only to dilute drugs according to the drug manufacturer's instructions.⁵ For a prescribed HCG product, those instructions point to the diluent in the kit. What the full name on a vial certifies is explained in our USP label guide.

10. Summary

• HCG is prescription-only; the product label and prescriber govern the diluent and use.
• Novarel: Bacteriostatic Water for Injection, 0.9% benzyl alcohol; 30 days refrigerated after mixing.
• Pregnyl: Water for Injection with 0.56% sodium chloride and 0.9% benzyl alcohol; 60 days refrigerated; do not freeze.
• Generic Chorionic Gonadotropin for Injection, USP: bacteriostatic water, 10 mL; 60 days refrigerated.
• Ovidrel is a ready-to-use recombinant syringe.
• Sterile water removes the preservative the labels' storage periods depend on.
• FDA: HCG is not approved without a prescription for any purpose, and no HCG product is approved for weight loss.