Corticotropin (ACTH 1-39)
ACTH, adrenocorticotropic hormone, adrenocorticotrophin, corticotrophin, ACTH(1-39), repository corticotropin injection (porcine)
ACTH 1-39 is the full-length pituitary hormone that drives the adrenal gland to make cortisol. Its first thirteen residues correspond to alpha-MSH, so it also engages melanocortin receptors on immune cells and melanocytes. Marketed as repository corticotropin injection, it has real randomised evidence in infantile spasms and comparatively thin evidence for its many other approved indications - a mismatch that has made it one of the most scrutinised drug-pricing controversies in the United States.
Mechanism
ACTH is a 39-amino-acid peptide cleaved from proopiomelanocortin (POMC) in corticotroph cells of the anterior pituitary, corresponding to residues 138-176 of the human POMC precursor. Its release is driven by hypothalamic CRH and arginine vasopressin and restrained by cortisol negative feedback. Its canonical target is MC2R on the adrenal zona fasciculata, a Gs-coupled receptor that uniquely requires the accessory protein MRAP for surface expression and function. MC2R activation raises cAMP, activates protein kinase A, and drives StAR-mediated cholesterol transport into mitochondria - the rate-limiting step in steroidogenesis - increasing cortisol output within minutes and, with chronic stimulation, causing adrenocortical hypertrophy.
What makes ACTH 1-39 more than a cortisol-releasing hormone is its N-terminal thirteen residues, which are the same sequence as alpha-MSH (alpha-MSH is that fragment with an acetylated N-terminus and an amidated C-terminus). ACTH is therefore also an agonist at MC1R, MC3R and MC5R, receptors expressed on melanocytes, macrophages, monocytes, lymphocytes, adipocytes, renal podocytes and microglia. This is the basis of the claim, made for repository corticotropin products, that ACTH has steroid-independent anti-inflammatory and immunomodulatory activity: melanocortin signalling on immune cells suppresses NF-kappaB and shifts macrophages towards a resolving phenotype. It is a biologically plausible claim, supported by cell and animal work. It has also never been cleanly separated in humans from the far simpler explanation that ACTH works because it makes cortisol - and a great deal of commercial value has rested on that unresolved distinction. The MC1R activity separately explains the hyperpigmentation characteristic of Addison's disease and Nelson's syndrome, where circulating ACTH is chronically very high.
What the research shows
The strongest human evidence for full-length ACTH is in infantile spasms (West syndrome). A prospective randomised single-blind trial found high-dose repository corticotropin markedly superior to prednisone: complete cessation of spasms with resolution of hypsarrhythmia occurred in 13 of 15 infants (86.6%) on corticotropin 150 U/m2/day versus 4 of 14 (28.6%) on prednisone 2 mg/kg/day over two weeks. The trial enrolled 29 infants in total, was single-blind, and the prednisone comparator dose has since been argued to have been sub-therapeutic - but hormonal therapy for infantile spasms is now firmly established. An important qualification: the larger UK Infantile Spasms Study, which randomised 107 infants and found spasm cessation at 14 days in 40 of 55 (73%) on hormonal treatment versus 28 of 52 (54%) on vigabatrin, used a hormonal arm consisting of prednisolone (n=30) or tetracosactide, synthetic ACTH 1-24 (n=25) - not full-length ACTH 1-39. It is supporting context for hormonal therapy in general, not for this molecule specifically.
Outside infantile spasms the evidence for repository corticotropin is thin relative to how widely and how expensively it is used, and two of the modern trials were outright negative. A randomised controlled withdrawal trial in refractory rheumatoid arthritis enrolled 259 patients and randomised 154 responders; 61% on continued treatment versus 42.1% on placebo maintained low disease activity (p=0.019) - a positive result, but a withdrawal design that never tested the drug against a conventional corticosteroid. A phase 4 placebo-controlled trial in persistently active systemic lupus erythematosus did not meet its primary endpoint: SRI-4 response at week 16 was 47.6% versus 43.5% on placebo (p=0.5762). A randomised comparison against intravenous methylprednisolone in 37 patients with acute optic neuritis found no neuroprotective advantage (retinal nerve fibre layer loss -13.1 vs -11.7 micrometres, p=0.88). None of these establishes superiority over conventional corticosteroids for the conditions in which the product is most heavily prescribed, and several were manufacturer-sponsored. Health-economics researchers and a 2020 US congressional investigation both concluded that a substantial proportion of the approved indications rest on evidence that would not support approval today.
Two further points of confusion are worth clearing up. The standard clinical ACTH stimulation test does not use ACTH 1-39 - it uses cosyntropin or tetracosactide, the synthetic 1-24 fragment, which retains full MC2R activity with lower immunogenicity. And the marketed repository products are not purified ACTH 1-39 either: they are porcine pituitary extracts in gelatin whose major component is N25-deamidated porcine ACTH 1-39 alongside other pituitary peptides. Anything sold online as 'ACTH 1-39' is a synthetic peptide with no clinical characterisation whatsoever.
Evidence assessment
Mixed evidence
There is genuine randomised evidence in infantile spasms, but that trial enrolled 29 infants and was single-blind, and for most other labelled indications the controlled data are sparse, decades old, grandfathered from a 1952 approval, or manufacturer-sponsored - with the lupus and optic neuritis trials failing to show benefit over placebo or over conventional corticosteroid.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
High-dose corticotropin (ACTH) versus prednisone for infantile spasms: a prospective, randomized, blinded study Mixed evidence
Complete cessation of spasms with resolution of hypsarrhythmia occurred in 13 of 15 infants (86.6%) on corticotropin versus 4 of 14 (28.6%) on prednisone.
The United Kingdom Infantile Spasms Study comparing vigabatrin with prednisolone or tetracosactide at 14 days: a multicentre, randomised controlled trial High-quality evidence
Cessation of spasms at 14 days occurred in 40 of 55 (73%) on hormonal treatment versus 28 of 52 (54%) on vigabatrin (difference 19%, p=0.043), with similar adverse event rates (55% vs 54%) and no deaths.
Repository Corticotropin Injection for Active Rheumatoid Arthritis Despite Aggressive Treatment: A Randomized Controlled Withdrawal Trial Mixed evidence
Among open-label responders, 61% on continued repository corticotropin versus 42.1% on placebo maintained low disease activity (p=0.019). The withdrawal design does not test the drug against conventional corticosteroids.
Repository Corticotropin Injection for Persistently Active Systemic Lupus Erythematosus: Results from a Phase 4, Multicenter, Randomized, Double-Blind, Placebo-Controlled Trial Mixed evidence
The trial did not meet its primary endpoint: SRI-4 response at week 16 was 47.6% with repository corticotropin versus 43.5% with placebo (p=0.5762). Some secondary joint and skin measures improved, and post hoc subgroup analyses favoured the active arm.
A Randomized Prospective Trial Comparing Repository Corticotropin Injection and Intravenous Methylprednisolone for Neuroprotection in Acute Optic Neuritis Mixed evidence
No clinically meaningful difference between treatments: peripapillary retinal nerve fibre layer loss was -13.1 micrometres versus -11.7 micrometres (p=0.88), with both arms improving on visual function and patient-reported outcomes.
Safety
ACTH carries the full adverse-effect burden of high-dose glucocorticoids, because generating them is how it works: hypertension, fluid retention, hypokalaemia, hyperglycaemia and new-onset diabetes, immunosuppression with increased infection risk including reactivation of latent infection, osteoporosis, myopathy, cataract and glaucoma, mood disturbance and frank psychosis, growth suppression in children, and adrenal suppression on withdrawal requiring a taper. In infants treated for spasms, irritability, hypertension, infection and reversible cerebral atrophy on imaging are recognised. Because repository products are animal-derived, hypersensitivity reactions and neutralising antibodies are additional concerns, and live vaccines are contraindicated during treatment. It is contraindicated in scleroderma, osteoporosis, systemic fungal infection, ocular herpes simplex, recent surgery, peptic ulcer, congestive heart failure, uncontrolled hypertension, adrenocortical hyperfunction, and primary adrenocortical insufficiency - where it cannot work, since the adrenal cortex is the target.
There is no safety information at all for synthetic ACTH 1-39 self-administered outside clinical care. A compound whose defining action is to drive endogenous cortisol production, with the capacity to suppress the hypothalamic-pituitary-adrenal axis on withdrawal, is particularly hazardous to take without monitoring.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | No repository corticotropin product is licensed in the UK. The MHRA-licensed corticotrophic agent is tetracosactide (synthetic ACTH 1-24), used principally for the short Synacthen adrenal stimulation test and, in depot form, occasionally therapeutically. Full-length ACTH 1-39 has no UK marketing authorisation, and any synthetic ACTH 1-39 sold as a research peptide is unlicensed and unlawful to supply for human use. |
| United States | Repository corticotropin injection (a porcine pituitary extract in gelatin) is FDA-approved for infantile spasms in infants and children under 2, for acute exacerbations of multiple sclerosis, and for a long list of rheumatic, collagen, dermatological, allergic, ophthalmic, respiratory and oedematous conditions largely grandfathered from a 1952 approval. Prescription-only and specialty-distributed. It has been the subject of sustained pricing controversy - the price per vial rose from roughly $40 around 2000 to tens of thousands of dollars - together with a US congressional investigation and whistleblower litigation over marketing practices. Synthetic human ACTH 1-39 as such is not an approved product; the approved adrenal diagnostic agent is cosyntropin, the 1-24 fragment. |
| WADA (sport) | Prohibited at all times. WADA's Prohibited List section S2.2 prohibits corticotrophins and their releasing factors (corticorelin is a named example), and ACTH 1-39 falls squarely within that class. Glucocorticoids themselves are separately prohibited in competition under section S9. BioRx was unable to re-verify the full current list text, so athletes should consult the current annual Prohibited List directly. |
Questions
No, and this is a common confusion. The standard short Synacthen or cosyntropin test uses tetracosactide, the synthetic ACTH 1-24 fragment. It retains full activity at the adrenal MC2 receptor because the first 24 residues contain everything needed for adrenal stimulation, but it is less immunogenic than the full-length peptide. Full ACTH 1-39 is not used diagnostically.
Largely because no competitor can duplicate it. It is not purified ACTH 1-39 but a porcine pituitary extract in gelatin, a complex mixture that cannot be shown bioequivalent by the usual generic route. That barrier, combined with an approval dating to 1952 that grandfathered in a long list of indications never tested by modern standards, allowed the price to rise from roughly $40 a vial around 2000 to tens of thousands. It has since attracted a congressional investigation and whistleblower litigation.
It plausibly does. ACTH's first thirteen residues are the alpha-MSH sequence, so it activates MC1R, MC3R and MC5R on macrophages, lymphocytes, podocytes and microglia, where melanocortin signalling suppresses NF-kappaB and shifts immune cells towards resolution. That mechanism is real in cell and animal work. What has never been demonstrated in humans is that this steroid-independent effect produces clinical benefit beyond what the cortisol alone would deliver - and a great deal of commercial argument has depended on that unresolved question. The one head-to-head trial against intravenous methylprednisolone, in acute optic neuritis, found no advantage.
They are the risks of high-dose corticosteroid therapy, because that is what ACTH produces: hypertension, hyperglycaemia and new-onset diabetes, hypokalaemia, immunosuppression and serious infection, bone loss, cataract, glaucoma, psychiatric disturbance, and adrenal suppression that can cause a crisis on abrupt withdrawal. Unlike a steroid tablet, the effect is mediated by the adrenal gland itself, so it cannot simply be stopped and reversed. Nothing about the safety of self-administered synthetic ACTH 1-39 has ever been studied.