ACTH: The Adrenal Cortisol Peptide

Pituitary Peptide Hormones

39 amino acids

ACTH is cleaved from the 241-amino-acid precursor POMC and drives cortisol synthesis from the adrenal cortex. Its fragments have spawned drugs for cognition, sexual function, and skin pigmentation.

Behan et al., Molecular Psychiatry, 1996

Behan et al., Molecular Psychiatry, 1996

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Every morning, before you wake, your pituitary gland releases a surge of adrenocorticotropic hormone (ACTH) into the bloodstream. This 39-amino-acid peptide travels to the adrenal cortex and triggers cortisol synthesis, preparing your body for the metabolic demands of the day. By evening, ACTH levels fall to their nadir, completing a circadian cycle that repeats with remarkable precision. Antonijevic et al. (2000) demonstrated that this rhythm interacts with other peptide systems, showing that neuropeptide Y administration to healthy young men promoted sleep while simultaneously inhibiting ACTH and cortisol release, revealing the interconnection between sleep-wake peptide circuits and the stress axis.^[1]

ACTH occupies a central position in peptide biology for two reasons. First, it is the primary driver of the hypothalamic-pituitary-adrenal (HPA) axis, the neuroendocrine system that mediates the body's response to physical and psychological stress. Second, it is derived from proopiomelanocortin (POMC), one of the most remarkable precursor proteins in biology: a single polypeptide that generates ACTH, alpha-melanocyte-stimulating hormone (alpha-MSH), beta-endorphin, and several other bioactive peptides depending on which enzymes process it in which tissues. For the broader overview of pituitary peptide hormone biology, see prolactin: the milk-producing peptide hormone.

From One Precursor, Many Peptides

ACTH is not synthesized directly. It is cleaved from proopiomelanocortin (POMC), a 241-amino-acid precursor protein encoded by a single gene on chromosome 2. POMC is expressed primarily in corticotroph cells of the anterior pituitary, in neurons of the arcuate nucleus of the hypothalamus, and in cells of the skin, immune system, and gut.

The peptides generated from POMC depend on which prohormone convertase enzymes are present in a given tissue. In anterior pituitary corticotrophs, prohormone convertase 1 (PC1) cleaves POMC to produce ACTH (amino acids 1-39) and beta-lipotropin (beta-LPH). In the hypothalamus and intermediate lobe (in species that retain one), prohormone convertase 2 (PC2) further processes ACTH into alpha-MSH (ACTH 1-13) and CLIP (corticotropin-like intermediate lobe peptide, ACTH 18-39), and cleaves beta-LPH into beta-endorphin. L'Hereault et al. (1991) studied the regulation of POMC mRNA in primary pituitary cell cultures, demonstrating that opioid peptides themselves feed back to regulate POMC transcription, creating a self-modulating loop between POMC-derived products.^[2]

Low et al. (2003) examined the state-dependent modulation of feeding behavior by POMC-derived beta-endorphin, showing that the same precursor protein produces peptides with opposite metabolic effects: alpha-MSH suppresses appetite (through melanocortin-4 receptors) while beta-endorphin stimulates reward-driven eating (through mu-opioid receptors).^[3] This means POMC is not simply a hormone factory; it is a metabolic switch whose output depends on tissue-specific processing. Genetic mutations that disrupt POMC processing cause severe early-onset obesity, adrenal insufficiency, and red hair pigmentation, because alpha-MSH, ACTH, and beta-endorphin are all lost simultaneously.

Elliott et al. (2004) extended this further by demonstrating that alpha-MSH, the KPV tripeptide fragment (MSH 11-13), and ACTH itself all signal through melanocortin receptors in human keratinocytes, with implications for skin pigmentation, inflammation, and wound healing.^[4] The POMC system thus connects the stress response (ACTH/cortisol), pain modulation (beta-endorphin), appetite regulation (alpha-MSH), and skin biology through a single precursor.

The HPA Axis: How ACTH Release Is Controlled

ACTH secretion is driven primarily by corticotropin-releasing hormone (CRH), a 41-amino-acid peptide produced by parvocellular neurons in the paraventricular nucleus of the hypothalamus. CRH travels through the hypophyseal portal system to the anterior pituitary, where it binds CRH receptor type 1 (CRH-R1) on corticotroph cells. Behan et al. (1996) reviewed the neurobiology of CRH receptors and CRH-binding protein, establishing that two CRH receptor subtypes (CRH-R1 and CRH-R2) mediate different aspects of the stress response: CRH-R1 primarily drives anxiety-like behaviors and ACTH secretion, while CRH-R2 is involved in appetite regulation, cardiovascular responses, and stress recovery.^[5]

Arginine vasopressin (AVP) acts as a co-secretagogue, amplifying the ACTH-releasing effect of CRH when both peptides are released simultaneously. During chronic stress, the ratio of CRH to AVP shifts: CRH levels may decrease (due to receptor downregulation) while AVP levels increase, maintaining ACTH drive through a different receptor pathway. This AVP-mediated shift is one reason chronic stress produces sustained cortisol elevation even when the initial CRH surge has attenuated. For more on vasopressin's broader roles, see vasopressin (ADH): the water-conserving peptide hormone.

Reul and Holsboer (2002) reviewed the role of CRH-R1 and CRH-R2 in anxiety and depression, noting that chronically elevated CRH and ACTH are found in a significant proportion of patients with major depression, and that CRH-R1 antagonists represent a potential therapeutic target for stress-related psychiatric disorders.^[6] The HPA axis dysregulation in depression is not simply "high cortisol"; it involves altered CRH receptor sensitivity, impaired negative feedback at glucocorticoid receptors, and changes in ACTH pulsatility.

Negative feedback completes the circuit. Cortisol binds two types of receptors with different affinities: mineralocorticoid receptors (MR), which have high affinity and are occupied at basal cortisol levels, and glucocorticoid receptors (GR), which have lower affinity and are occupied only during stress-induced cortisol peaks. This two-receptor system creates a threshold effect: basal cortisol maintains tonic HPA axis suppression through MR, while stress-level cortisol activates GR to terminate the acute stress response. GR activation in the hypothalamus and pituitary suppresses CRH and ACTH transcription. This is the basis of the dexamethasone suppression test: exogenous glucocorticoids should suppress ACTH and cortisol through GR activation. Failure to suppress indicates autonomous ACTH production (Cushing's disease), ectopic ACTH secretion by a tumor, or disrupted feedback (as seen in approximately 50% of patients with melancholic depression).

Arvat et al. (1997) demonstrated that growth hormone-releasing peptides (GHRP-2 and hexarelin) stimulate not only GH but also ACTH and cortisol release in a dose-dependent manner, providing evidence that the GH and HPA axes share regulatory peptide inputs.^[7] This cross-talk means that peptide therapies targeting the GH axis can have unintended effects on cortisol regulation, and vice versa.

When ACTH Goes Wrong: Cushing's Disease and Adrenal Insufficiency

Cushing's disease results from a pituitary corticotroph adenoma that secretes excess ACTH autonomously, driving chronic hypercortisolism. Symptoms include central obesity, moon face, striae, hypertension, diabetes, osteoporosis, depression, and immunosuppression. The condition affects approximately 10-15 per million people. First-line treatment is transsphenoidal surgical resection of the adenoma, but recurrence rates range from 15-66% depending on follow-up duration.

Ceccato et al. (2015) reviewed the clinical use of pasireotide (a multi-receptor somatostatin analog) for Cushing's disease, reporting that pasireotide normalized urinary free cortisol in up to 28% of patients, with a mean cortisol reduction of approximately 50% at the 600-900 microgram twice-daily dose.^[8] Pasireotide works because corticotroph adenomas express somatostatin receptor 5 (SSTR5), and pasireotide's high SSTR5 affinity allows it to suppress ACTH secretion from the tumor. Hyperglycemia occurred in 73% of patients, driven by SSTR5-mediated insulin suppression (a challenge also discussed in the context of somatostatin biology).

Boehm et al. (2024) described peptide receptor radionuclide therapy (PRRT) for ectopic Cushing's syndrome caused by metastatic neuroendocrine neoplasms that secrete ACTH, demonstrating that targeting somatostatin receptors on the ACTH-producing tumor cells with radiolabeled peptides can reduce both tumor burden and cortisol levels in treatment-refractory cases.^[9]

Adrenal insufficiency (Addison's disease in its primary form) is the opposite: insufficient cortisol production leads to compensatory ACTH elevation. The elevated ACTH acts on melanocortin-1 receptors in the skin, causing hyperpigmentation, particularly in sun-exposed areas, skin creases, and mucous membranes. This pigmentation is a direct consequence of ACTH's structural relationship to alpha-MSH: the first 13 amino acids of ACTH are identical to alpha-MSH, giving ACTH melanotropic activity at high circulating concentrations. The pigmentation pattern often provides the first clinical clue to diagnosis, appearing months before other symptoms of adrenal insufficiency become apparent.

The diagnostic peptide cosyntropin (Cortrosyn, Synacthen) is synthetic ACTH(1-24), the first 24 amino acids of natural ACTH. It retains full adrenal-stimulating activity and is used in the ACTH stimulation test to evaluate adrenal reserve. A normal cortisol response to cosyntropin injection rules out primary adrenal insufficiency.

ACTH Fragments as Drugs: Semax and Beyond

One of the most distinctive features of ACTH is that different fragments of the molecule have different biological activities. The N-terminal region (amino acids 1-24) drives adrenal cortisol production. But the central fragment ACTH(4-10) has no adrenal activity whatsoever; instead, it has cognitive-enhancing (nootropic) and neuroprotective properties.

Eremin et al. (2005) demonstrated that Semax, a synthetic analog of ACTH(4-10) with a Pro-Gly-Pro tripeptide extension for metabolic stability, activates dopaminergic and serotonergic brain systems in rats without any effect on cortisol or adrenal function.^[10] This dissociation between adrenal and neurological effects demonstrates that ACTH is not one hormone; it is a collection of overlapping functional domains within a single peptide chain.

Glazova et al. (2021) showed that Semax attenuated behavioral and neurochemical alterations following early-life immune challenges in rats, suggesting neuroprotective effects that extend to developmental neurobiology.^[11] Inozemtseva et al. (2024) demonstrated antidepressant-like and antistress effects of Semax and Melanotan II (another POMC-derived analog) in male rats, with Semax reversing stress-induced behavioral despair through mechanisms involving BDNF upregulation in the hippocampus.^[12]

Liu et al. (2025) revealed a novel mechanism for Semax's neuroprotective effects: targeting the mu-opioid receptor gene Oprm1 to promote deubiquitination and functional recovery after spinal cord injury.^[13] This connects the ACTH fragment back to the opioid system through POMC biology: ACTH and beta-endorphin share a precursor, and fragments of each can modulate opioid signaling.

Semax is approved in Russia for stroke, cognitive disorders, and optic nerve atrophy, but has not been evaluated in Western regulatory clinical trials. It is administered as a nasal spray (0.1% solution), with intranasal delivery bypassing first-pass hepatic metabolism and providing relatively rapid CNS access. The Pro-Gly-Pro C-terminal extension increases Semax's half-life from seconds (for native ACTH 4-10) to several minutes, sufficient for therapeutic effects. The Gravanis et al. (2005) review of CRF family neuropeptides in inflammation further documented that ACTH fragments and related melanocortin peptides have anti-inflammatory properties independent of cortisol, mediated through melanocortin receptors on immune cells.^[14]

What ACTH Research Has Not Resolved

The pulsatile nature of ACTH secretion is well documented but poorly understood mechanistically. ACTH is released in approximately 15-18 secretory bursts per day, and the amplitude of these bursts varies with circadian time, stress, and metabolic state. Whether pulsatility itself carries information that tonic ACTH cannot (similar to the pulsatile GH secretion question) remains unresolved.

The role of ACTH in non-adrenal tissues is another open area. POMC is expressed in immune cells, and ACTH can bind melanocortin receptors on macrophages and lymphocytes. Whether locally produced ACTH in immune tissues has physiological relevance, or is simply an evolutionary vestige, is debated.

The clinical development of CRH receptor antagonists for depression and anxiety has been disappointing despite strong preclinical rationale. Multiple CRH-R1 antagonists have failed in phase II/III clinical trials, suggesting that the HPA axis dysfunction in depression may be a consequence rather than a cause, or that CRH-R1 antagonism alone is insufficient to normalize the multiple pathways involved. An alternative interpretation is that the CRH system has too much redundancy (AVP co-secretion, CRH-R2 compensation, cortisol-independent CRH effects on behavior) for single-receptor blockade to produce measurable clinical improvement.

The therapeutic potential of ACTH fragment peptides beyond Semax also remains underexplored in Western medicine. ACTH(1-17), known as alpha-MSH's extended precursor, has anti-inflammatory properties mediated through melanocortin-3 and melanocortin-4 receptors. Whether synthetic ACTH fragments could be developed as anti-inflammatory peptide drugs, distinct from the full-length hormone's cortisol-stimulating properties, is a question that connects ACTH biology to the broader melanocortin pharmacology pipeline.

For context on how ACTH fits into the broader pituitary peptide landscape, see the pituitary gland: the peptide hormone headquarters and FSH and LH: the gonadotropin peptides that drive reproduction. For the related topic of opioid peptides derived from the same POMC precursor, see beta-endorphin: the runner's high peptide.

The Bottom Line

ACTH is a 39-amino-acid peptide derived from the POMC precursor that drives cortisol production through the HPA axis. Its biology extends beyond the adrenal gland: POMC processing generates alpha-MSH, beta-endorphin, and other bioactive peptides, while ACTH fragments like Semax demonstrate nootropic and neuroprotective properties independent of cortisol. Clinical applications span Cushing's disease treatment (pasireotide, PRRT), adrenal insufficiency diagnosis (cosyntropin), and cognitive enhancement (Semax).

Frequently Asked Questions

What does ACTH do in the body?

ACTH (adrenocorticotropic hormone) is a 39-amino-acid peptide released by the anterior pituitary that stimulates the adrenal cortex to produce cortisol. It follows a circadian rhythm, peaking at 6-8 AM and reaching its lowest point around midnight. Antonijevic et al. (2000) showed that ACTH release is integrated with sleep-wake cycles, with neuropeptide Y promoting sleep while simultaneously suppressing ACTH and cortisol.

What is POMC and how does it relate to ACTH?

POMC (proopiomelanocortin) is a 241-amino-acid precursor protein from which ACTH is cleaved. Different enzymes in different tissues cut POMC into different peptides: the anterior pituitary produces ACTH and beta-lipotropin, while the hypothalamus produces alpha-MSH and beta-endorphin. Low et al. (2003) demonstrated that POMC-derived peptides have opposing metabolic effects, with alpha-MSH suppressing appetite and beta-endorphin stimulating reward eating.

What is Cushing's disease?

Cushing's disease is caused by a pituitary adenoma that secretes excess ACTH, leading to chronic hypercortisolism. Symptoms include central obesity, hypertension, diabetes, osteoporosis, and depression. It affects approximately 10-15 per million people. Ceccato et al. (2015) reported that pasireotide (a somatostatin analog) normalized cortisol in up to 28% of patients, though hyperglycemia occurred in 73% due to insulin suppression.

What is Semax peptide?

Semax is a synthetic analog of ACTH(4-10), the central fragment of ACTH that has no cortisol-stimulating activity but demonstrates cognitive-enhancing and neuroprotective properties. Eremin et al. (2005) showed it activates dopaminergic and serotonergic brain systems. It is approved in Russia for stroke and cognitive disorders. Liu et al. (2025) revealed it promotes functional recovery after spinal cord injury through opioid receptor modulation.

What is the ACTH stimulation test?

The ACTH stimulation test uses cosyntropin (synthetic ACTH 1-24) to evaluate adrenal gland function. A dose of 250 micrograms is injected intravenously or intramuscularly, and cortisol is measured at 30 and 60 minutes. A cortisol rise to above 18-20 micrograms/dL is considered normal. Failure to respond suggests primary adrenal insufficiency (Addison's disease), where the adrenal glands cannot produce cortisol despite ACTH stimulation.

Why does high ACTH cause skin darkening?

ACTH shares its first 13 amino acids with alpha-MSH (alpha-melanocyte-stimulating hormone), giving it melanotropic activity. In conditions with chronically elevated ACTH, such as Addison's disease, the excess ACTH activates melanocortin-1 receptors on skin melanocytes. Elliott et al. (2004) confirmed that both alpha-MSH and ACTH signal through melanocortin receptors in human keratinocytes, explaining the hyperpigmentation seen in skin creases, scars, and sun-exposed areas.