# What is the half-life of growth hormone? Minutes in a vein, hours under the skin Updated 2026-10-16. Somatropin, or growth hormone, has a half-life of 0.4 hours when given into a vein, in normal adults, on the Genotropin label. Given under the skin, the Genotropin label gives 3.0 hours in adults lacking growth hormone, and the Humatrope label gives 3.8 hours in healthy people. Both labels say the longer figure comes from slow absorption under the skin. | | | | --- | --- | | Intravenous half-life, Genotropin | 0.4 hours, mean terminal, normal adults ([Genotropin, BLA 020280](https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=020280)) | | Subcutaneous half-life, Genotropin | 3.0 hours, adults with growth hormone deficiency | | Subcutaneous half-life, Humatrope | 3.8 hours (SD 1.4), healthy subjects ([Humatrope, BLA 019640](https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=019640)) | | Reason for the longer figure | Slow absorption from the site under the skin (both labels) | | Half-life of GHRP-6 (immunoreactive peptide) | 20 minutes after oral and intravenous use in normal men (Bowers et al., 1992) | | Records checked | 16 October 2026 | Ask how long growth hormone lasts and you can get two answers that sound wildly different: less than half an hour, or three to four hours. It is easy to think two different hormones are being described. They are not. It is one molecule, measured after it entered the body by two different routes. A half-life is how long the body takes to remove half of a substance from the blood. After one half-life, half is left. After two, a quarter is left. This page belongs to [the growth hormone peptides hub](/learn/growth-hormone-peptides). It reads the numbers straight off two FDA labels for the hormone described on [the somatropin page](/learn/growth-hormone-peptides/what-is-somatropin). It explains why the numbers differ. It also says which half-lives the hub does not give, because no source we opened reports them. ## What half-life do the FDA labels give for somatropin? The Genotropin label gives a half-life of 0.4 hours when somatropin goes straight into a vein (intravenous use). That was measured in normal adults. The same label gives 3.0 hours when somatropin goes under the skin (subcutaneous use), measured in adults whose bodies make too little growth hormone. The Humatrope label gives 3.8 hours for use under the skin in healthy people. Its standard deviation is 1.4 hours, which shows how much people varied. The 0.4-hour figure is a "terminal" half-life. That means it was taken from the last, slow phase as the blood level falls. Two products and two groups of people were measured. So the figures should not be blended into one number. The two under-the-skin values differ by 0.8 hours. The groups differ too. One label measured adults lacking growth hormone. The other measured healthy people. The table below sets the three figures side by side. ## Why is the intravenous half-life so much shorter than the subcutaneous one? Both labels give the same reason: slow absorption. The Genotropin label says the difference comes from slow absorption from the spot under the skin. The Humatrope label says the same about its longer figure. When somatropin goes into a vein, all of it is in the blood at once. So the measurement shows only how fast the body clears it. When somatropin goes under the skin, it seeps into the blood over several hours. So the measurement also captures that slow entry. The hormone itself has not changed. Only the way it reaches the blood is different. Picture a bath with the plug pulled out. Water draining away is clearance. A slow tap still running into the bath is absorption. If you watch both at once, the bath seems to empty slowly, even though the drain never changed. The 3.0 and 3.8 hour figures describe the tap as much as the drain. The Humatrope label adds two more numbers from healthy people after a single use under the skin. The blood level peaked after a median of 4.0 hours, with a range of 3 to 8 hours. The absolute bioavailability was 75%. Bioavailability is the share of the hormone that reaches the blood. The Genotropin label also says where the hormone goes. The liver and kidneys break it down the usual way the body breaks down proteins. ![Two bathtubs with drains the same size, labelled Same drain. The left tub, labelled Into a vein, has no tap and is nearly empty. The right tub, labelled Under the skin, has a Slow tap still running and holds more water.](/assets/content/edu-bath-tap-and-drain.png) Somatropin into a vein has a half-life of 0.4 hours; under the skin it is 3.0 to 3.8 hours, because it seeps in slowly while the body clears it at the same rate. Sources: Genotropin and Humatrope prescribing information (FDA). ## How do these figures compare with growth hormone-releasing peptides? These figures cannot be compared directly with the releasing peptides. Those are different molecules, measured in different studies. A 1992 study of GHRP-6 found that the peptide stayed in the blood with a half-life of 20 minutes in normal men. That was measured after both swallowed and intravenous use, by tracking the peptide with antibodies (immunoreactive GHRP-6). But a peptide's half-life only tells you how long that peptide stays in the blood. It does not tell you how long growth hormone stays raised afterwards. How long a peptide lasts and how the hormone responds are two separate measurements. A 2006 study of CJC-1295 with DAC in healthy adults estimated its half-life at 5.8 to 8.1 days. DAC is a chemical hook that makes the peptide stick to albumin, a common blood protein. [The CJC-1295 hub](/learn/cjc-1295) puts that figure in context. [The HGH versus releasing peptides page](/learn/growth-hormone-peptides/hgh-vs-growth-hormone-releasing-peptides) compares the other families, and [the GHRP-2 and GHRP-6 hub](/learn/ghrp-2-and-ghrp-6) covers GHRP-6 in more depth. These somatropin, GHRP-6 and CJC-1295 records do not give half-lives for AOD-9604 or IGF-1 LR3. ## Comparison The half-life of somatropin as printed on two FDA labels, by route and by the group of people measured. The last column gives the reason each label states. This is a record of measurements, not a ranking. | Label and route | People measured | Half-life | What the number mostly reflects | | --- | --- | --- | --- | | Genotropin, into a vein (intravenous) | Normal adults | 0.4 hours (mean terminal) | Clearance only, because there is no slow absorption step | | Genotropin, under the skin (subcutaneous) | Adults with growth hormone deficiency | 3.0 hours | Slow absorption from under the skin, plus clearance | | Humatrope, under the skin (subcutaneous) | Healthy subjects | 3.8 hours (SD 1.4) | Slow absorption from under the skin, plus clearance | ## Frequently asked questions ### Is the 3 to 4 hour figure how long growth hormone works? No. The figure is the measured half-life of somatropin in the blood after use under the skin. Both labels say its length comes from slow absorption. A half-life describes how much of the molecule is in the blood. It does not describe how long its effects last. ### Why is the intravenous half-life only 0.4 hours? The Genotropin label gives 0.4 hours as the mean terminal half-life when somatropin goes into a vein in normal adults. There is no slow absorption step, so the number shows clearance alone. The label says the liver and kidneys break the hormone down the usual way the body breaks down proteins. ### Has the half-life of every growth hormone-releasing peptide been measured? The sources cited here give half-lives for somatropin, GHRP-6 and CJC-1295. They do not show whether every other releasing peptide has been measured. This page does not claim that such measurements are missing. ## Citations - Bowers CY, Alster DK, Frentz JM.. Journal of Clinical Endocrinology and Metabolism. 1992;74(2):292-298. DOI: 10.1210/jcem.74.2.1730807 - Teichman SL, Neale A, Lawrence B, Gagnon C, Castaigne JP, Frohman LA.. Journal of Clinical Endocrinology & Metabolism. 2006;91(3):799-805. DOI: 10.1210/jc.2005-1536 --- Canonical page: https://www.formlaboratories.com/learn/growth-hormone-peptides/somatropin-half-life Form Laboratories - Perth-based research-use-only peptide supplier, shipping Australia-wide. - Site guide for agents: https://www.formlaboratories.com/llms.txt - Sitemap: https://www.formlaboratories.com/sitemap.xml - Full catalogue: https://www.formlaboratories.com/shop - Contact: hello@formlaboratories.com All materials are supplied for laboratory research use only - not for human or veterinary use, and nothing on this site is medical advice.