Research HGH: IU vs mg, Vial Sizes & Reconstitution Math

Human growth hormone (HGH), or somatropin, is a 191-amino acid single-chain polypeptide identical in sequence to the growth hormone secreted by the anterior pituitary. In a research context it is supplied as a lyophilised (freeze-dried) powder that must be reconstituted before use. The single fact that trips up most reconstitution and handling work is that somatropin is quantified in International Units (IU), a measure of biological activity, rather than in milligrams of mass. The rest of this guide is about working with that IU measurement: converting it to mass, reading vial labels, and calculating reconstitution volumes. For the underlying GH/IGF-1 biology and the GH axis, and for compounds that stimulate the body's own GH release, see the dedicated guide below.

For research use only. Not for human or animal consumption. HGH (somatropin) is a Schedule 4 prescription-only medicine in Australia for therapeutic use; OzPeps supplies it strictly for in-vitro laboratory and scientific research.

Studying GH secretagogues (GHRH analogues and ghrelin-receptor agonists) instead of exogenous HGH? That is a separate topic covered in full by the CJC-1295 & Ipamorelin research guide →.

Most research peptides are labelled by mass (for example, a 10mg vial of a GHRH analogue). HGH is different: it is labelled by International Units (IU), a standardised measure of biological potency rather than weight. This convention exists because growth hormone preparations are calibrated against an international activity standard, so an "IU" describes how much GH activity is present, not how many milligrams of protein.

For modern recombinant somatropin the widely used approximate conversion is:

• 1 mg ≈ 3 IU (equivalently, 1 IU ≈ 0.33 mg)

This 1:3 ratio is an approximation tied to the recombinant somatropin activity standard and can vary slightly by formulation, so always treat a vial's stated IU value as the source of truth rather than back-calculating mass. Applying the approximation to the OzPeps vial presentations gives:

The practical takeaway: when a protocol or calculator asks for "mg" but your vial is labelled in IU, convert with the 1mg ≈ 3IU ratio, and when planning reconstitution work directly in IU wherever possible to avoid compounding rounding error.

OzPeps stocks HGH in several IU presentations. The label has two numbers: the IU per vial and the number of vials, which multiply to the kit total. Choosing a presentation is about matching per-vial IU and total IU to a protocol's concentration and duration requirements, not about potency differences between products. For short pilot work, a single 40IU vial covers protocol testing without committing to a full 10-vial kit.

A higher per-vial IU (40IU vs 10IU) means more activity is concentrated in one vial, so a fixed water volume yields a higher IU-per-mL concentration. That is the key variable the reconstitution math below turns into a number. All OzPeps HGH is supplied as lyophilised powder with a verified supplier Certificate of Analysis (COA).

Reconstitution converts a dry vial of known IU into a liquid of known concentration. The only inputs are the vial's IU and the volume of bacteriostatic water added; the relationship is linear:

Core formula
Concentration (IU per mL) = Vial IU ÷ Water added (mL)
Volume to draw (mL) = Target IU ÷ Concentration (IU per mL)

Worked examples using the OzPeps presentations and the same fixed 1 mL of bacteriostatic water, so the only thing changing is the vial's IU:

Two things follow directly from the formula. First, adding more water lowers the concentration proportionally: putting 2 mL into a 40IU vial gives 20 IU/mL instead of 40 IU/mL, doubling the volume you draw for the same target and making small measurements easier. Second, higher-IU vials need more water to reach a workably measurable concentration, because at a fixed water volume each measured fraction represents more IU. Choose the water volume so that your target IU corresponds to a volume your measuring equipment can read accurately.

To skip the arithmetic, the OzPeps reconstitution calculator takes vial IU, water volume and target dose and returns the volume to draw.

HGH reconstitution follows the same general procedure as other lyophilised peptides, covered step by step in the peptide reconstitution & storage guide. Two points are specific to somatropin:

• Use bacteriostatic water (0.9% benzyl alcohol) rather than plain sterile water. The preservative extends post-reconstitution stability for multi-draw research use.
• Dry vials tolerate room temperature. Unlike many peptides that need refrigeration even when lyophilised, dry somatropin powder is comparatively stable at room temperature before reconstitution; refrigerate after reconstitution and protect from light.

Direct the bacteriostatic water gently down the vial wall rather than onto the powder cake, and let the vial stand to dissolve rather than shaking, to avoid mechanically stressing the protein.

This guide is deliberately scoped to measurement, vial selection and reconstitution — the practical specs of working with research HGH. For the biology of the GH/IGF-1 axis, somatopause, and the broader research applications of growth hormone signalling, and for compounds that stimulate endogenous GH release rather than supplying it directly, see:

• CJC-1295 & Ipamorelin research guide — GH secretagogues (GHRH analogues + ghrelin-receptor agonists), mechanism and comparison data
• Peptide reconstitution & storage guide — general reconstitution procedure
• Australian research peptide legality guide — TGA scheduling and "research use only"