Growth hormone treatment
Growth hormone treatment refers to the use of growth hormone (GH) as a prescription medication - it is one form of Hormone therapy. Growth hormone is a peptide hormone secreted by the pituitary gland that stimulates growth and cell reproduction. In the past, growth hormone was extracted from human pituitary glands. GH is now produced by recombinant DNA technology and is prescribed for a variety of reasons. GH therapy has been a focus of social and ethical controversies for 50 years.
This article describes the history of GH treatment, current uses and risks arising from GH use. Other articles describe GH physiology, diseases of GH excess (acromegaly and pituitary gigantism), deficiency, the recent phenomenon of HGH controversies, growth hormone in sports, and growth hormone for cows.
HGH deficiency in children
Growth hormone deficiency is treated by replacing GH. All GH prescribed in North America, Europe, and most of the rest of the world is a human GH, manufactured by recombinant DNA technology. As GH is a large peptide molecule, it must be injected into subcutaneous tissue or muscle to get it into the blood. Nearly painless insulin syringes make this less trying than is usually anticipated, but perceived discomfort is a subjective value.
When treated with GH, a deficient child will begin to grow faster within months. Other benefits may be noticed, such as increased strength, progress in motor development, and reduction of body fat. Side-effects of this type of physiologic replacement are quite rare. Known risks and unsettled issues are discussed below, but GH-deficient children receiving replacement doses are at the lowest risk for problems..
Still, costs of treatment in terms of money, effort, and perhaps quality of life are substantial. Treatment of children usually involves daily injections of growth hormone, usually for as long as the child is growing. Lifelong continuation may be recommended for those most severely deficient as adults. Most pediatric endocrinologists monitor growth and adjust dose every 3–4 months. Assessing the psychological value of treatment is difficult, but most children and families are enthusiastic once the physical benefits begin to be seen. Treatment costs vary by country and by size of child, but $US 10,000 to 30,000 a year is common.
Little except the cost of treating severely deficient children is controversial, and most children with severe growth hormone deficiency in the developed world are offered treatment. Most accept. The story is very different for adult deficiency.
HGH deficiency in adults
The Endocrine Society has recommended that adult patients diagnosed with grown hormone deficiency (GHd) be administered an individualized GH treatment regimen. With respect to diagnosis, their guidelines state that "adults patients with structural hypothalamic/pituitary disease, surgery or irradiation in these areas, head trauma, or evidence of other pituitary hormone deficiencies be considered for evaluation for acquired GHd" and that "idiopathic GHd in adults is very rare, and stringent criteria are necessary to make this diagnosis. Because in the absence of suggestive clinical circumstances there is a significant false-positive error rate in the response to a single GH stimulation test, we suggest the use of two tests before making this diagnosis."
GH replacement therapy can provide a number of measurable benefits to GH-deficient adults. These include improved bone density. increased Muscle mass, decrease of adipose tissue, faster hair and nail growth, strengthened immune system, increased circulatory system, and improved blood lipid levels, but long term mortality benefit has not yet been demonstrated.
A peer-review article published in 2010 indicates that "Growth hormone (GH) replacement unequivocally benefits growth, body composition, cardiovascular risk factors and quality of life. Less is known about the effects of GH on learning and memory."
As of 2004, GH has been approved by the U.S. Food and Drug Administration for treatment of other conditions:
- Turner syndrome epitomizes the response of non-deficient shortness. At doses 20% higher than those used in GH deficiency, growth accelerates. With several years of treatment the median gain in adult height is about 2–3 in (5.1–7.6 cm) on this dose. The gains appear to be dose-dependent. It has been used successfully in toddlers with Turner syndrome, as well as in older girls.
- Chronic renal failure results in many problems, including growth failure. GH treatment for several years both before and after transplantation may prevent further deceleration of growth and may narrow the height deficit, though even with treatment net adult height loss may be about 4 in (10 cm)
- Prader-Willi syndrome, a generally non-hereditary genetic condition, is a case where GH is prescribed for benefits in addition to height. GH is one of the treatment options an experienced endocrinologist may use when treating a child with PWS. GH can help children with PWS in height, weight, body mass, strength, and agility.. Reports have indicated increase of growth rate (especially in the first year of treatment) and a variety of other positive effects, including improved body composition (higher muscle mass, lower fat mass); improved weight management; increased energy and physical activity; improved strength, agility, and endurance; and improved respiratory function. The Prader-Willi Syndrome Association (USA) recommends that a sleep study be conducted before initiating GH treatment in a child with PWS. At this time there is no direct evidence of a causative link between growth hormone and the respiratory problems seen in PWS (among both those receiving and those not receiving GH treatment), including sudden death. A follow-up sleep study after one year of GH treatment may also be indicated. GH (specifically Pfizer's version, Genotropin) is the only treatment that has received an FDA indication for children with PWS. The FDA indication only applies to children.
- Children short because of intrauterine growth retardation are small for gestational age at birth for a variety of reasons. If early catch-up growth does not occur and their heights remain below the third percentile by 2 or 3 years of age, adult height is likely to be similarly low. High-dose GH treatment has been shown to accelerate growth, but data on long term benefits and risks are limited.
- Idiopathic short stature (ISS) is one of the most controversial indications for GH as pediatric endocrinologists do not agree on its definition, diagnostic criteria, or limits. The term has been applied to children with severe unexplained shortness that will result in an adult height below the 3rd percentile. In the late 1990s, the pharmaceutical manufacturer Eli Lilly and Company sponsored trials of Humatrope (their brand of rHGH) in children with extreme ISS, those at least 2.25 standard deviations below mean (in the lowest 1.2 percent of the population). These boys and girls appeared to be headed toward heights of less than 63" (160 cm) and 59" (150 cm) respectively. They were treated for about 4 years and gained 1.5–3 in (3.8–7.6 cm) in adult height. Controversy has arisen as to whether all of these children were truly "short normal" children, since the average IGF1 was low. It was not surprising that approval for this extreme degree of shortness led to an increase in the number of parents seeking treatment to make otherwise healthy children a little taller.
The New England Journal of Medicine published two editorials in 2003 expressing concern about off-label uses of HGH and the proliferation of advertisements for "HGH-Releasing" dietary supplements, and emphasized that there is no evidence that use of HGH in healthy adults or in geriatric patients is safe and effective - and especially emphasized that risks of long-term HGH treatment are unknown. One editorial was by Jeffrey M. Drazen, M.D., the editor-in-chief of the journal; the other one was by Dr. Mary Lee Vance, who provided the NEJM's editorial original, cautious comment on a much cited 1990 study on the use of HGH in geriatric patients with low growth hormone levels.
A small but controlled study of GH given to severely ill adults in an intensive care unit setting for the purpose of increasing strength and reducing the muscle wasting of critical illness showed a higher mortality rate for the patients having received GH. The reason is unknown, but GH is now rarely used in ICU patients unless they have severe growth hormone deficiency.
In past it was believed that GH treatment could increase the cancer risk; a large study recently concluded that "With relatively short follow-up, the overall primary cancer risk in 6840 patients receiving GH as adults was not increased. Elevated SIRs (which is risk of getting cancer) were found for subgroups in the USA cohort defined by age <35 years or childhood onset GH deficiency."
The FDA issued a Safety Alert in August 2011, communicating the fact that a French study found that persons with certain kinds of short stature (idiopathic growth hormone deficiency and idiopathic or gestational short stature) treated with recombinant human growth hormone during childhood and who were followed over a long period of time, were at a small increased risk of death when compared to individuals in the general population of France.
Perhaps the most famous person who exemplified the appearance of untreated congenital growth hormone deficiency was Charles Sherwood Stratton (1838–1883), who was exhibited by P.T. Barnum as General Tom Thumb, and married Lavinia Warren. Pictures of the couple show the typical adult features of untreated severe growth hormone deficiency. Despite the severe shortness, limbs and trunks are proportional.
Like many other nineteenth-century medical terms that lost precise meaning as they gained wider currency, “midget,” as a term for someone with extreme proportional shortness, acquired pejorative connotations and is no longer used in medical contexts.
By the middle of the twentieth century, endocrinologists understood the clinical features of growth hormone deficiency. GH is a protein hormone, like insulin, which had been purified from pig and cow pancreases for treatment of type 1 diabetes since the 1920s. However, pig and cow GH did not work at all in humans, due to greater species-to-species variation of molecular structure (i.e., insulin is considered more "evolutionarily conserved" than GH).
Extraction for treatment
Extracted growth hormone was used since late 1950s until late 1980s when its use was replaced by recombinant GH.
In the late 1950s, Maurice Raben purified enough GH from human pituitary glands to successfully treat a GH-deficient boy. A few endocrinologists began to help parents of severely GH-deficient children to make arrangements with local pathologists to collect human pituitary glands after removal at autopsy. Parents would then contract with a biochemist to purify enough growth hormone to treat their child. Few families could manage such a complicated undertaking.
In 1960, the National Pituitary Agency was formed as a branch of the U.S. National Institutes of Health. The purpose of this agency was to supervise the collection of human pituitary glands when autopsies were performed, arrange for large-scale extraction and purification of GH, and distribute it to a limited number of pediatric endocrinologists for treating GH-deficient children under research protocols. Canada, UK, Australia, New Zealand, France, Israel, and other countries establish similar government-sponsored agencies to collect pituitaries, purify GH, and distribute it for treatment of severely GH-deficient children.
Supplies of this “cadaver growth hormone” were limited, and only the most severely deficient children were treated. From 1963 to 1985 about 7700 children in the U.S. and 27,000 children worldwide were given GH extracted from human pituitary glands to treat severe GH deficiency. Physicians trained in the relatively new specialty of pediatric endocrinology provided most of this care, but in the late 1960s there were only a hundred of these physicians in a few dozen of the largest university medical centers around the world.
In 1976, physicians became aware that Creutzfeldt-Jacob disease could be transmitted by neurosurgical procedures and cornea transplantation. CJD is a rapidly fatal dementing disease of the brain also known as spongiform encephalopathy, related to “mad cow disease”.
In 1977, the NPA GH extraction and purification procedure was refined and improved.
A shortage of available cadaver GH worsened in the late 1970s as the autopsy rate in the U.S. declined, while the number of pediatric endocrinologists able to diagnose and treat GH deficiency increased. GH was "rationed." Often, treatment would be stopped when a child reached an arbitrary minimal height, such as 5 ft 0 in (1.52 m). Children who were short for reasons other than severe GH deficiency were lied to and told that they would not benefit from treatment. Only those pediatric endocrinologists that remained at university medical centers with departments able to support a research program had access to NPA growth hormone.
In the late 1970s, a Swedish pharmaceutical company, Kabi, contracted with a number of hospitals in Europe to buy pituitary glands for the first commercial GH product, Crescormon. Although an additional source of GH was welcomed, Crescormon was greeted with ambivalence by pediatric endocrinologists in the United States. The first concern was that Kabi would begin to purchase pituitaries in the U.S., which would quickly undermine the NPA, which relied on a donation system like blood transfusion. As the number of autopsies continued to shrink, would pathologists sell pituitaries to a higher bidder? The second offense was Kabi-Pharmacia’s marketing campaign, which was directed at primary care physicians under the slogan, “Now, you determine the need,” implying that the services of a specialist were not needed for growth hormone treatment anymore and that any short child might be a candidate for treatment. Although the Crescormon controversy in the U.S. is long forgotten, Kabi’s pituitary purchase program continued to generate scandal in Europe as recently as 2000.
Recombinant human growth hormone (rHGH)
In 1981, the new American corporation Genentech, after collaboration with Kabi, developed and started trials of recombinant human growth hormone (rHGH) made by a new technology (recombinant DNA) in which human genes were inserted into bacteria so that they could produce unlimited amounts of the protein. Because this was new technology, approval was deferred as lengthy safety trials continued over the next four years.
In 1985, four young adults in the U.S. having received NPA growth hormone in the 1960s developed CJD (Creutzfeldt-Jacob disease). The connection was recognized within a few months, and use of human pituitary GH rapidly ceased. Between 1985 and 2003, a total of 26 cases of CJD occurred in adults having received NPA GH before 1977 (out of 7700), comparable numbers of cases occurred around the world. By 2003 there had been no cases in people who received only GH purified by the improved 1977 methods.
Discontinuation of human cadaver growth hormone led to rapid Food and Drug Administration approval of Genentech’s recombinant human growth hormone, which was introduced in 1985 as Protropin in the United States. Although this previously scarce commodity was suddenly available in “bucketfuls,” the price of treatment (US$10,000–30,000 per year) was the highest at the time. Genentech justified it by the prolonged research and development investment, orphan drug status, and a pioneering post-marketing surveillance registry for tracking safety and effectiveness (National Cooperative Growth Study).
Within a few years, GH treatment had become “big business” in more than one sense. Eli Lilly launched a competing natural sequence growth hormone (Humatrope). Pharmacia (formerly Kabi, now Pfizer) introduced Genotropin. Novo Nordisk introduced Norditropin. Serono (now EMD Serono) introduced Saizen and Serostim and Serostim. Ferring has introduced Zomacton. Genentech eventually introduced another HGH product, Nutropin, and stopped making Protropin in 2004. Price competition has begun. Teva, which is primarily a generics company, has introduced Tev-tropin. Chinese companies have entered the market as well and have introduced more pricing competition: NeoGenica BioScience Ltd. introduced Hypertropin/; GeneScience Pharmaceutical Co., Ltd. has introduced Jintropin; Anhui Anke Biotechnology has introduced Ansomone. (There are reports of a product called Fintropin sold by the Chinese biotech firm, Kexing, but as of December 2011, their website does not report that they produce rHGH.) These are all recombinant human growth hormone products and they have competed with various marketing strategies. Most children with severe deficiency in the developed world are now likely to have access to a pediatric endocrinologist and be diagnosed and offered treatment.
Pediatric endocrinology became a recognizable specialty in the 1950s, but did not reach board status in the U.S. until the late 1970s. Even 10 years later, as a cognitive, procedureless specialty dealing with mostly rare diseases, it was one of the smallest, lowest-paid, and more obscure of the medical specialities. Pediatric endocrinologists were the only physicians interested in the arcana of GH metabolism and children’s growth, but their previously academic arguments took on new practical significance with major financial implications.
The major scientific arguments dated back to the days of GH scarcity:
- Everyone agrees on the nature and diagnosis of severe GH deficiency, but what are the edges and variations?
- How should marked constitutional delay be distinguished from partial GH deficiency?
- To what extent is “normal shortness” a matter of short children naturally making less growth hormone?
- Can a child make GH in response to a stimulation test but fail to make enough in “daily life” to grow normally?
- If a stimulation test is used to define deficiency, what GH cutoff should be used to define normal?
It was the ethical questions that were new. Is GH not a wise use of finite healthcare resources, or is the physician’s primary responsibility to the patient? If GH is given to most extremely short children to make them taller, will the definition of “extremely short” simply rise, negating the expected social benefit? If GH is given to short children whose parents can afford it, will shortness become a permanent mark of lower social origins? More of these issues are outlined in the ethics section. Whole meetings were devoted to these questions; pediatric endocrinology had become a specialty with its own bioethics issues.
Despite the price, the 1990s became an era of experimentation to see what else growth hormone could help. The medical literature of the decade contains hundreds of reports of small trials of GH use in nearly every type of growth failure and shortness imaginable. In most cases, the growth responses were modest. For conditions with a large enough potential market, more rigorous trials were sponsored by pharmaceutical companies that were making growth hormone to achieve approval to market for those specific indications. Turner syndrome and chronic renal failure were the first of these “nonGH-deficient causes of shortness” to receive FDA approval for GH treatment, and Prader-Willi syndrome and intrauterine growth retardation followed. Similar expansion of use occurred in Europe.
One obvious potential market was adult GH deficiency. By the mid-1990s, several GH companies had sponsored or publicized research into the quality of life of adults with severe GH deficiency. Most were people having been treated with GH in childhood for severe deficiency. Although the injections are painless, many of them had been happy to leave injections behind as they reached final heights in the low-normal range. However, as adults in their 30s and 40s, these people, who had been children with growth hormone deficiency, were now adults with growth hormone deficiency and had more than their share of common adult problems: reduced physical, mental, and social energy, excess adipose and diminished muscle, diminished libido, poor bone density, higher cholesterol levels, and higher rates of cardiovascular disease. Research trials soon confirmed that a few months of GH could improve nearly all of these parameters. However, despite marketing efforts, most GH-deficient adults remain untreated.
Though GH use was slow to be accepted among adults with GH deficiency, similar research to see if GH treatment could slow or reverse some of the similar effects of aging attracted much public interest. The most publicized trial was reported by Daniel Rudman in 1990. As with other types of hormone supplementation for aging (testosterone, estrogen, DHEA), confirmation of benefit and accurate understanding of risks has been only slowly evolving.
There are always entrepreneurs who do not need much evidence to see a business opportunity. In 1997, Ronald Klatz of the American Academy of Anti-Aging Medicine published Grow Young With HGH: The Amazing Medically Proven Plan To Reverse the Effects Of Aging, an uncritical touting of GH as the answer to aging.: This time, the internet amplified the proposition and spawned a hundred frauds and scams. However, their adoption of the "HGH" term has provided an easy way to distinguish the hype from the evidence. In 2003, growth hormone hit the news again, when the US FDA granted Eli Lilly approval to market Humatrope for the treatment of idiopathic short stature. The indication was controversial for several reasons, the primary one being the difficulty in defining extreme shortness with normal test results as a disease rather than the extreme end of the normal height range
Recombinant growth hormone available in the U.S. (and their manufacturers) included Nutropin (Genentech), Humatrope (Eli Lilly and Company), Genotropin (Pfizer), Norditropin (Novo Nordisk), Tev-Tropin (Teva) and Saizen (Merck Serono). The products are nearly identical in composition, efficacy, and cost, varying primarily in the formulations and delivery devices.
Growth hormone (GH l) is also called somatotropin (British: somatotrophin). The human form of growth hormone is known as human growth hormone, or hGH (ovine growth hormone, or sheep growth hormone, is abbreviated oGH). GH can refer either to the natural hormone produced by the pituitary (somatotropin), or biosynthetic GH for therapy.
Cadaver growth hormone is the term for GH extracted from human pituitary glands between 1960 and 1985 for therapy of deficient children. In the U.S., cadaver GH, also referred to as NPA growth hormone, was provided by the National Pituitary Agency, and by other national programs and commercial firms as well. In 1985 it was associated with the development of Creutzfeldt-Jakob Disease, and was withdrawn from use.
rHGH refers to recombinant human growth hormone (somatropin). Its amino acid sequence is identical with that of endogenous human GH.
It is coincidental that rHGH also refers to rhesus monkey GH, using the accepted naming convention. Rhesus growth hormone was never used by physicians to treat human patients, but rhesus GH was part of the lore of the underground anabolic steroid community in those years, and fraudulent versions may have been bought and sold in gyms.
met-GH refers to methionyl-growth hormone. This was the first recombinant GH product marketed (Protropin by Genentech). It had the same amino acid sequence as human GH with an extra methionine at the end of the chain to facilitate the manufacturing process. It was discontinued in 2004.
rBST refers to recombinant bovine somatropin (cow growth hormone), or recombinant bovine GH (rbGH).
- Molitch ME et al. (2011) Evaluation and Treatment of Adult Growth Hormone Deficiency:An Endocrine Society Clinical Practice Guideline The Endocrine Society, 2011. First published in Journal of Clinical Endocrinology & Metabolism, 96(6):1587–1609.
- Götherström G, Bengtsson BA, Bosaeus I, Johannsson G, Svensson J (January 2007). "Ten-year GH replacement increases bone mineral density in hypopituitary patients with adult onset GH deficiency". Eur. J. Endocrinol. 156 (1): 55–64. doi:10.1530/eje.1.02317. PMID 17218726.
- Alexopoulou O, Abs R, Maiter D (2010). "Treatment of adult growth hormone deficiency: who, why and how? A review". Acta Clin Belg 65 (1): 13–22. PMID 20373593.
- Ahmad AM, Hopkins MT, Thomas J, Ibrahim H, Fraser WD, Vora JP (June 2001). "Body composition and quality of life in adults with growth hormone deficiency; effects of low-dose growth hormone replacement". Clin. Endocrinol. (Oxf) 54 (6): 709–17. doi:10.1046/j.1365-2265.2001.01275.x. PMID 11422104.
- Savine R, Sönksen P (2000). "Growth hormone - hormone replacement for the somatopause?". Horm. Res. 53 Suppl 3: 37–41. doi:10.1159/000023531. PMID 10971102.
- Götherström G, Bengtsson BA, Bosaeus I, Johannsson G, Svensson J (April 2007). "A 10-year, prospective study of the metabolic effects of growth hormone replacement in adults". J. Clin. Endocrinol. Metab. 92 (4): 1442–5. doi:10.1210/jc.2006-1487. PMID 17284638.
- Wass JA, Reddy R (November 2010). "Growth hormone and memory". J. Endocrinol. 207 (2): 125–6. doi:10.1677/JOE-10-0126. PMID 20696696.
- Bolar K, Hoffman AR, Maneatis T, Lippe B (February 2008). "Long-term safety of recombinant human growth hormone in turner syndrome". J. Clin. Endocrinol. Metab. 93 (2): 344–51. doi:10.1210/jc.2007-1723. PMID 18000090.
- Davenport ML, Crowe BJ, Travers SH, Rubin K, Ross JL, Fechner PY, Gunther DF, Liu C, Geffner ME, Thrailkill K, Huseman C, Zagar AJ, Quigley CA (September 2007). "Growth hormone treatment of early growth failure in toddlers with Turner syndrome: a randomized, controlled, multicenter trial". J. Clin. Endocrinol. Metab. 92 (9): 3406–16. doi:10.1210/jc.2006-2874. PMID 17595258.
- Backeljauw P (February 2008). "Does growth hormone therapy before 4 years of age enhance the linear growth of girls with Turner's syndrome?". Nat Clin Pract Endocrinol Metab 4 (2): 78–9. doi:10.1038/ncpendmet0678. PMID 17971794.
- Chatelain P, Carrascosa A, Bona G, Ferrandez-Longas A, Sippell W (2007). "Growth hormone therapy for short children born small for gestational age". Horm. Res. 68 (6): 300–9. doi:10.1159/000107935. PMID 17823537.
- Czernichow P (March 2008). "Which children with idiopathic short stature should receive growth hormone therapy?". Nat Clin Pract Endocrinol Metab 4 (3): 118–9. doi:10.1038/ncpendmet0700. PMID 18040291.
- Hannon TS, Danadian K, Suprasongsin C, Arslanian SA (August 2007). "Growth hormone treatment in adolescent males with idiopathic short stature: changes in body composition, protein, fat, and glucose metabolism". J. Clin. Endocrinol. Metab. 92 (8): 3033–9. doi:10.1210/jc.2007-0308. PMID 17519313.
- Drazen JM (February 2003). "Inappropriate advertising of dietary supplements". N. Engl. J. Med. 348 (9): 777–8. doi:10.1056/NEJMp030021. PMID 12606730.
- Vance ML (February 2003). "Can growth hormone prevent aging?". N. Engl. J. Med. 348 (9): 779–80. doi:10.1056/NEJMp020186. PMID 12606731.
- Takala J, Ruokonen E, Webster NR, Nielsen MS, Zandstra DF, Vundelinckx G, Hinds CJ (September 1999). "Increased mortality associated with growth hormone treatment in critically ill adults". N. Engl. J. Med. 341 (11): 785–92. doi:10.1056/NEJM199909093411102. PMID 10477776.
- Bramnert M, Segerlantz M, Laurila E, Daugaard JR, Manhem P, Groop L (April 2003). "Growth hormone replacement therapy induces insulin resistance by activating the glucose-fatty acid cycle". J. Clin. Endocrinol. Metab. 88 (4): 1455–63. doi:10.1210/jc.2002-020542. PMID 12679422.
- Attanasio AF, Jung H, Mo D, Chanson P, Bouillon R, Ho KK, Lamberts SW, Clemmons DR (July 2011). "Prevalence and incidence of diabetes mellitus in adult patients on growth hormone replacement for growth hormone deficiency: a surveillance database analysis". J. Clin. Endocrinol. Metab. 96 (7): 2255–61. doi:10.1210/jc.2011-0448. PMID 21543424.
- Child CJ, Zimmermann AG, Woodmansee WW, Green DM, Li JJ, Jung H, Erfurth EM, Robison LL (August 2011). "Assessment of primary cancers in GH-treated adult hypopituitary patients: an analysis from the Hypopituitary Control and Complications Study". Eur. J. Endocrinol. 165 (2): 217–23. doi:10.1530/EJE-11-0286. PMC 3132593. PMID 21646285.
- "Recombinant Human Growth Hormone (somatropin): Ongoing Safety Review - Possible Increased Risk of Death". Safety Information. U.S. Food and Drug Administration. 2011-04-08.
- Rudman D, Feller AG, Nagraj HS, Gergans GA, Lalitha PY, Goldberg AF, Schlenker RA, Cohn L, Rudman IW, Mattson DE (July 1990). "Effects of human growth hormone in men over 60 years old". N. Engl. J. Med. 323 (1): 1–6. doi:10.1056/NEJM199007053230101. PMID 2355952.
- Ronald Klatz and Carol Kahn. Grow Young With Hgh: The Amazing Medically Proven Plan to : Lose Fat, Build Muscle, Reverse the Effects of Aging, Strengthen the Immune System, Improve Sexual Performance. Harpercollins; 1st edition (April 1997) ISBN: 0060186828
- Blackman MR, et al (2002) Growth hormone and sex steroid administration in healthy aged women and men: a randomized controlled trial. JAMA 288(18):2282-92.
- Olshansky SJ et al (2002) Position Statement on Human Aging Journal of Gerontology 57A(8):B292–B297
- Leona Cuttler (2005) Editorial: Safety and Efficacy of Growth Hormone Treatment for Idiopathic Short Stature. The Journal of Clinical Endocrinology & Metabolism 90(9):5502-5504
- Weiss JO, Hall JG (September 1991). "Support Groups for Individuals with Growth Problems and their Families" (PDF). Growth Genet Horm 7 (3).
- "Considerations Related to the Use of Recombinant Human Growth Hormone in Children" (PDF). Growth Genet Horm 14 (1). April 1998.
-  Prader-Willi Syndrome Association (USA)