Lonapegsomatropin (Skytrofa)_Dosage, benefits & legal status
Also known as Skytrofa, lonapegsomatropin-tcgd, TransCon hGH, ACP-011
Most of the injection is packaging designed to fall off.
Common vial size is what vendors typically sell, not a recommendation. Enter your own vial in the calculator.
What is Lonapegsomatropin (Skytrofa)?
Plain language first. The technical label stays, but it never stands alone.Overview
This is the cleverest of the three weekly growth hormones and the easiest to misunderstand. Most of what gets injected is not a drug at all: it is a polyethylene glycol carrier, about two thirds of the molecule's weight, attached to real growth hormone by a linker engineered to snap itself at a steady rate. While attached, the hormone does nothing. As the week goes on the linker cuts itself and releases ordinary growth hormone a bit at a time. This is the same mechanism the Yuviwel page on this site describes for a different hormone, from the same company. It is also the only one of the three that beat daily growth hormone in its trial rather than just matching it.
Lonapegsomatropin is a long-acting prodrug of somatropin. The label describes somatropin conjugated to a methoxypolyethylene glycol carrier, four arms of 10 kilodaltons each, joined through a proprietary TransCon linker, giving a 63 kilodalton molecule from which 22 kilodaltons of somatropin is released by autocleavage of the linker. While conjugated the hormone is inactive; the label states the product releases fully active somatropin. Dose strengths are expressed in somatropin equivalents, so the stated milligrams exclude the carrier. The prodrug half-life is 30.7 hours and the released somatropin about 25 hours. It is approved for children aged 1 year and older weighing at least 11.5 kg with growth hormone deficiency, and for adults with growth hormone deficiency.
What it's used for
Growth failure from inadequate growth hormone secretion in children aged 1 year and older who weigh at least 11.5 kg, and growth hormone replacement in adults with a deficiency.
How does Lonapegsomatropin (Skytrofa) work?
What it does in the body, and where.This site already explains this trick on the Yuviwel page, for a different hormone from the same company. Here it is applied to growth hormone itself.
- 01Two thirds packaging, one third drugThe injected molecule is 63 kilodaltons. Of that, four arms of methoxypolyethylene glycol at 10 kilodaltons each make up about 41 kilodaltons of inert carrier, and the somatropin it carries is 22 kilodaltons. While the hormone is attached to the carrier it cannot bind its receptor. The carrier is not a delivery aid in the usual sense; it is a chemical restraint.
- 02A linker that cuts itselfThe two halves are joined by what the manufacturer calls a TransCon linker, engineered to cleave itself at a predictable first-order rate without needing an enzyme. Over the week it steadily lets go, so the dose is released gradually rather than delivered at once. The label describes the result as releasing fully active somatropin by autocleavage of the linker.
- 03What is actually released, stated preciselyThe released molecule is somatropin, and this is the only one of the three weekly products that delivers growth hormone rather than a permanently altered version of it. Be careful with the wording though: the label says fully active somatropin and the European summary says it has the same mode of action and distribution as daily somatropin. Neither regulator uses the word unmodified, so that word should not be put in their mouths.
- 04Why the dose number is smaller than it looksBecause the strength counts somatropin equivalents, the 0.24 mg/kg on this label refers only to the hormone being delivered, not to the 63 kilodalton molecule containing it. Somapacitan's label also says 0.24 mg/kg for its short-stature indications, and that number counts a whole modified protein including its side chain. Two identical-looking numbers measuring different things is the most practical confusion in this group.
- 05The one that beat daily treatmentIn its pivotal pediatric trial against daily somatropin, this product did not merely show non-inferiority: the registry record shows the comparison went on to demonstrate superiority on annualized height velocity. Somapacitan and somatrogon both matched daily treatment without beating it. That makes this the strongest efficacy claim in the group, and a prodrug design is the plausible reason: the hormone released is the real thing.
A schematic of the compound's mechanism, not a diagnostic image.
What else is it used for?
Each group carries its own evidence level.Approved means regulators have cleared it for that purpose. Investigational means it is in trials. Early research means it is being studied and is not established.
The only prodrug, and the only one to beat daily treatment
FDA-approved- Regulatory63 kilodalton molecule, of which about 41 kilodaltons is inert methoxypolyethylene glycol carrier and 22 kilodaltons is the somatropin it releases.
- RegulatoryThe linker cleaves itself at a steady rate without an enzyme, releasing what the label calls fully active somatropin.
- Human trialIn its pivotal pediatric trial against daily somatropin the registry record shows the comparison went beyond non-inferiority to superiority on annualized height velocity. The other two weekly products matched daily treatment without beating it.
Half-life, and the dose-mass trap
FDA-approved- RegulatoryProdrug half-life 30.7 hours with a standard deviation of 12.7; released somatropin about 25 hours. Nothing close to a week.
- No dataStrengths are stated in somatropin equivalents, so 0.24 mg/kg excludes the carrier. Somapacitan's 0.24 mg/kg counts a whole modified protein. The numbers look identical and measure different things.
- No dataThe label is internally inconsistent on this: three sections say somatropin equivalents while section 11 lists cartridge content as the conjugate.
Same carrier technology as a compound already on this site
FDA-approved- ReviewThe TransCon carrier and self-cleaving linker are the same platform this site already describes on the navepegritide page, applied there to natriuretic peptide and here to growth hormone.
- human-earlyThe two have been given together in the COACH trial in achondroplasia, as the navepegritide page already reports. That combination is not approved.
The most common claim about this product, including in otherwise careful writing, is that it releases unmodified or identical growth hormone. The substance of that is right, and the wording is not something a regulator said: the FDA label says fully active somatropin and the European summary says the same mode of action and distribution as daily somatropin. Use their words. Second, the 0.24 mg/kg dose is not comparable to somapacitan's 0.24 mg/kg, because this one counts only the hormone and excludes a carrier that is most of the molecule's mass. Third, a weekly injection does not mean a week-long drug: 30.7 hours for the prodrug and about 25 hours for the hormone it releases. Fourth, this is the only one of the three with a superiority result against daily growth hormone, so a general statement that long-acting growth hormones merely match daily treatment is wrong for this one and right for the other two.
The published record
Papers and trials about Lonapegsomatropin (Skytrofa)
Searched: lonapegsomatropin, Skytrofa, TransCon hGH, heiGHt.
Left out: growth hormone (tens of thousands of unrelated records); somatropin (the unmodified hormone released by this prodrug, and it has its own slug as HGH; including it would make this row unreadable); TransCon (the carrier platform, shared with navepegritide, which has its own slug and its own page explaining the same technology); navepegritide (has its own slug; the two were combined in the COACH trial and that result already sits on that page); PEG (a polymer used in hundreds of unrelated products).
227 papers tagged human · 197 not reviews or lab · 20 clinical trial publications
8 registered trials · 2 with posted results
Furthest stage reached: Approved in the US
Counted from Europe PMC indexing, not read by a person; a human tag can land on reviews, commentary or lab papers; clinical trial publications is the narrower count. 500 papers and 8 trials indexed in detail.
At a glance
Four things to know about Lonapegsomatropin (Skytrofa)
Evidence
FDA-approved
Category
Growth hormone
Common vial
Varies
Half-life
About 31 hours for the prodrug, 25 hours for the hormone it releases
How much, and do you cycle it?
The range, and whether you take breaks.0.24 mg/kg weekly, once weekly. Continuous weekly dosing while growth plates are open, or indefinitely in adults FDA label
Growth hormone replacement is continuous treatment, with at least 5 days between doses per the label. No cycling scheme applies.
How long does it stay in the body?
The half-life, and where the figure comes from.About 31 hours for the prodrug, 25 hours for the hormone it releasesFDA label
Prodrug 30.7 hours with a standard deviation of 12.7; released somatropin approximately 25 hours. Weekly dosing works because the carrier releases the hormone gradually across the week, not because any component lasts seven days.
Source: Skytrofa prescribing information, section 12.3
You can compare this against the whole library to see where it sits.
How is it given?
Dosing context and source notes.Supplied as a kit with its own diluent, and the label sets the volume, so there is nothing to work out here.
Label dose: 0.24 mg/kg per week.
0.24 mg/kg once weekly in children. The number counts somatropin equivalents, meaning only the hormone portion, and excludes the methoxypolyethylene glycol carrier that makes up most of the molecule's mass. A missed dose may be given within 2 days, and the label states at least 5 days should elapse between doses. Recorded as a prescribing fact, not as guidance.
How do you store it?
Before mixing, and after.Follow the storage on the product label.
Lonapegsomatropin (Skytrofa) is supplied as a finished product, so its label sets the storage. Pens, prefilled syringes, implants, tablets and ready-made solutions are used as supplied. Kits that include a powder are mixed just before the dose and usually used straight away, not kept for weeks. Many injectable products go in the fridge and must not be frozen, while others are kept at room temperature, so check the pack or ask the pharmacist.
What are the side effects and cautions?
Known cautions and warnings for this compound.Who should avoid it
- Any use outside a prescription: it needs a proprietary auto-injector and we found no vendor offering it
- Comparing its 0.24 mg/kg against somapacitan's 0.24 mg/kg as though they measured the same thing, because they do not
Stop and get help
- Signs of raised pressure inside the skull, such as persistent headache with vision changes or vomiting
- Signs of an allergic reaction to the injection
Common effects
- Injection-site reactions, headache and joint pain, as with growth hormone treatment generally
Where this page says nothing is established, that means nobody has studied it, not that a compound is safe.
Is Lonapegsomatropin (Skytrofa) approved?
And where the numbers on this page come from.Yes. Lonapegsomatropin (Skytrofa) is FDA approved and available on prescription in the United States. It is also approved in the European Union.
- Approval statusFDA-approved
- RouteUnder the skin (weekly injection)
- Checked30 October 2026
- Approved outside the USEuropean Union.This does not change the United States position above.
- DoseFrom the drug label. The manufacturer tested this range and a regulator reviewed it.
- Vial sizeFrom what vendors typically list; not a recommendation.
- Sources
What has happened recently
FDA-approved under BLA 761177 in August 2021 for pediatric growth hormone deficiency, with an adult indication added in July 2025. The current label covers children aged 1 year and older weighing at least 11.5 kg, and adults. One internal inconsistency in the label is worth flagging rather than resolving: sections 2.5, 2.6 and 16 state that strengths are expressed in somatropin equivalents, while section 11 lists cartridge contents as lonapegsomatropin itself. The 2026 WADA Prohibited List names lonapegsomatropin in section S2.2.3 as a growth hormone analog. The United Kingdom's Advisory Council on the Misuse of Drugs assessed it in 2025 and the medicines regulator reported no post-marketing misuse reports for it.
Banned in drug-tested sport. Most research peptides are prohibited under WADA's S0 category, which covers any substance with no approval from any regulatory authority for human use. That means a compound can be banned without ever being named on the prohibited list. Check with your own anti-doping authority rather than assuming absence from the list means permitted.
You can compare this against the whole library, or read how to check a seller.
What else is like Lonapegsomatropin (Skytrofa)?
Others in Growth hormone peptides, side by side.If you're weighing Lonapegsomatropin (Skytrofa), it's worth reading Macimorelin (Macrilen), Relamorelin, and Somapacitan (Sogroya) in the same class.
Most of the injection is packaging designed to fall off.
- Dose
- 0.24 mg/kg weekly
- How often
- Once weekly
An FDA-approved ghrelin agonist, and it is a diagnostic test rather than a treatment.
- Dose
- 0.5 mg per kg, once
- How often
- Single dose for the test
A ghrelin mimic tested in 1,564 people with diabetic gastroparesis, then stopped before any filing.
- Dose
- 10 mcg twice daily (phase 3); 10 to 100 mcg in earlier trials
- How often
- Twice daily (gastroparesis trials)
Weekly because albumin holds onto it, not because it lasts a week.
- Dose
- 0.16 to 0.24 mg/kg weekly
- How often
- Once weekly
Guides for this compound
- How to Reconstitute a Peptide
Mix peptide powder with bacteriostatic water, step by step.
- How to Read an Insulin Syringe
Read the units, convert to millilitres, and draw the exact dose.
- mcg vs mg: The Peptide Dosing Mistake to Avoid
Your vial says mg and your protocol says mcg. Here is the conversion and how to check it.
Sources
- Skytrofa (lonapegsomatropin-tcgd) prescribing information(2026)The label, read through the FDA's own label API. Describes a long-acting prodrug of a human growth hormone conjugated to a methoxypolyethylene glycol carrier, four arms of 10 kilodaltons, via a proprietary TransCon Linker, with a molecular weight of 63 kDa and released somatropin of 22 kDa. Section 12.3 states it releases fully active somatropin via autocleavage of the TransCon linker; the label does not use the words unmodified or identical. Section 11 gives a minimum potency of released somatropin of not less than 2.5 IU/mg. Sections 2.5, 2.6 and 16 state strengths in somatropin equivalents while section 11 lists cartridge content as lonapegsomatropin-tcgd, an internal inconsistency. Dose 0.24 mg/kg once weekly. Half-life of the prodrug 30.7 hours with a standard deviation of 12.7, and of released somatropin approximately 25 hours. A missed dose may be given not more than 2 days after. Indications: pediatric patients 1 year and older weighing at least 11.5 kg, and adults with growth hormone deficiency.
- WADA 2026 Prohibited List, section S2.2.3(2026)Section S2.2.3 names lonapegsomatropin, somapacitan and somatrogon among the growth hormone analogs. Section S2.2.4 names tesamorelin, sermorelin, CJC-1295, ipamorelin and ibutamoren, also called MK-677, all of which already have pages here.
- McDonnell and colleagues, European Journal of Endocrinology, the COACH trial(2026)Cited here because this site's navepegritide page already reports it from the other side. 21 children received navepegritide plus lonapegsomatropin; the 12 treatment-naive children grew 8.69 cm a year at week 52 against 5.95 cm a year in matched children on navepegritide alone. The combination is not approved. This page is consistent with that existing page by design.
Beyond these, 508 records are indexed. Browse the records