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Hormones & metabolism

Cosyntropin

Also called tetracosactide

EvidenceFDA approved

ClassACTH(1-24) analog

Cosyntropin is a synthetic ACTH fragment used to test adrenal function. Learn how the cortisol response is read and what FDA-approved means here.

Reviewed by: William Maish, MD MBA MPH, Clinical Product Lead
Published: October 5, 2026
Last updated: October 5, 2026

Key takeaway

Cosyntropin (sold as Cortrosyn) is a synthetic fragment of adrenocorticotropic hormone used as a diagnostic agent to test whether the adrenal glands are working. A dose is given and the resulting rise in cortisol shows how well the adrenals respond. It has long been FDA-approved in the U.S. and is given as a single injection during the test.

At a glance

What it is	Synthetic ACTH 1-24, the active portion of adrenocorticotropic hormone
Approved for	The ACTH stimulation test for adrenal insufficiency
Key fact	The cortisol response after a dose distinguishes normal from inadequate adrenal function
Route	Intravenous or intramuscular injection
Evidence strength	FDA approved

What is cosyntropin?

Cosyntropin, sold under the brand Cortrosyn, is a synthetic peptide made of the first 24 amino acids of adrenocorticotropic hormone (ACTH). Those 24 amino acids carry the full hormone's ability to stimulate the adrenal glands, so cosyntropin acts like natural ACTH but is simpler to manufacture and standardize. It is used not as a treatment but as a diagnostic agent. It is also known by the generic name tetracosactide. It has been FDA-approved for many years.

How does cosyntropin work?

Cosyntropin binds the melanocortin-2 receptor on the adrenal cortex, the same receptor as natural ACTH, and stimulates the adrenal glands to release cortisol. In the diagnostic test, a baseline cortisol level is measured, a dose of cosyntropin is given, and cortisol is measured again after a set interval. A healthy adrenal gland responds with a clear rise in cortisol; a blunted or absent rise points to adrenal insufficiency.

Because the value of the test lies in the measured response, cosyntropin is given as a single dose under controlled conditions. Studies comparing test protocols have examined lower and standard doses; a meta-analysis found the low-dose test was better than the standard dose at detecting chronic adrenal insufficiency¹ caused by the pituitary or hypothalamus. The test helps distinguish primary adrenal failure from other causes of low cortisol.

Is it FDA-approved?

Yes. Cosyntropin (Cortrosyn) has long been FDA-approved² as a diagnostic agent for screening adrenocortical insufficiency. It is given as a single injection, with cortisol measured before and after.

What is cosyntropin prescribed for?

Cosyntropin is used for the ACTH stimulation test, to evaluate whether the adrenal glands can produce cortisol normally. It is a diagnostic tool used by clinicians, not an ongoing therapy.

What are the side effects?

According to the prescribing information, reported side effects include:

Slow or fast heart rate
High blood pressure
Swelling in the hands or feet
Rash

More serious considerations include:

Allergic reactions, including anaphylaxis

More for hormones & metabolism

Sources: FDA prescribing information for Cortrosyn; a meta-analysis of corticotropin testing (Kazlauskaite et al., The Journal of Clinical Endocrinology & Metabolism, 2008, DOI: 10.1210/jc.2008-0710¹), indexed on PubMed. This document is educational and does not constitute medical advice.