Somatropin

Somatropin is structurally identical to pituitary-derived human GH. A single molecule binds two GH receptor subunits, triggering receptor dimerisation and JAK2 phosphorylation of STAT5, which drives transcription of IGF-1 in the liver and locally in tissues. The anabolic and growth effects are largely IGF-1 mediated, while the lipolytic and diabetogenic effects are direct GH receptor effects on adipose and muscle. Because it bypasses the pituitary entirely, there is no ceiling imposed by somatostatin or by IGF-1 negative feedback - which is why exogenous GH can produce acromegalic changes that no secretagogue can. It also suppresses the endogenous axis while it is running.

Targets: Growth hormone receptor (GHR), JAK2/STAT5 pathway, Hepatic IGF-1 production, Adipose lipolysis

• · Non-weight-based dosing starts at 0.2 mg (about 0.6 IU) daily and titrates by 0.1 to 0.2 mg every 1 to 2 months against IGF-1 and symptoms. Women on oral oestrogen typically need more.
• · 1 to 2 IU daily. 1 mg equals 3 IU. This range mostly stays within physiological IGF-1 and is where side effects remain manageable.
• · 3 to 6 IU daily. Carpal tunnel, oedema, insulin resistance and elevated IGF-1 become common and predictable in this range. Doses above 6 IU daily are where the acromegalic-appearance risk starts being real rather than theoretical.

Work out your exact syringe units →

• very commonPeripheral oedema and joint swelling— Dose-related and usually the first thing to appear.
• very commonArthralgia and myalgia
• commonCarpal tunnel syndrome— Numb hands on waking; responds to dose reduction.
• commonInsulin resistance and elevated fasting glucose— GH is directly counter-regulatory. Can unmask type 2 diabetes.
• uncommonInjection-site lipoatrophy— Rotate sites religiously.
• uncommonHypothyroidism unmasked or worsened— GH increases peripheral T4 to T3 conversion and can reveal marginal thyroid reserve.
• uncommonAdrenal insufficiency unmasked— GH inhibits 11-beta-HSD-1 and reduces cortisol regeneration, revealing previously compensated central adrenal insufficiency - a labelled warning. New fatigue, nausea, dizziness or hypotension after starting GH needs urgent cortisol assessment.
• rareIntracranial hypertension— Headache with visual change or papilloedema - stop and get assessed.
• rareAcromegalic changes - jaw, brow, hands, organ growth— Only with sustained supraphysiological dosing over years, and largely irreversible.
• rareSlipped capital femoral epiphysis in growing children— Paediatric-specific; new hip or knee pain warrants imaging.

• Active malignancy - GH and IGF-1 are proliferative signals.
• Acute critical illness after open-heart or abdominal surgery, multiple trauma or acute respiratory failure, where high-dose GH increased mortality in controlled trials.
• Active proliferative or severe non-proliferative diabetic retinopathy.
• Closed epiphyses when used for height promotion in children.
• Prader-Willi syndrome with severe obesity or severe respiratory impairment, where sudden deaths have been reported.
• Pregnancy.

• conflictinsulin — GH raises insulin requirements substantially; diabetics need active dose management.
• conflictGlucocorticoids — Supraphysiological steroids blunt GH's growth effect, and GH alters cortisone activation via 11-beta-HSD-1 - oral cortisone doses may need increasing.
• conflictOral oestrogen — Oral oestrogen substantially reduces the IGF-1 response to GH; transdermal does not. Women on oral oestrogen need higher GH doses.
• cautionLevothyroxine — GH can unmask central hypothyroidism; thyroid replacement often needs adjusting after starting.
• conflictipamorelin — Exogenous GH suppresses the endogenous axis, so a secretagogue has little left to release.
• conflictpegvisomant — Direct pharmacological opposites - GH receptor agonist versus antagonist.

• · IGF-1 every 6 to 8 weeks during titration, then every 6 to 12 months; target the mid-to-upper age-adjusted reference range.
• · Fasting glucose and HbA1c at baseline and at least annually.
• · Free T4 and TSH, since GH can unmask hypothyroidism.
• · Morning cortisol / adrenal status before starting and if symptoms suggest hypoadrenalism, particularly in anyone with hypopituitarism or prior pituitary surgery or irradiation.
• · Lipid panel and blood pressure.
• · In children: growth velocity, bone age and fundoscopy for intracranial hypertension.

FDA and EMA approved, prescription-only. In the United States, distributing or possessing hGH for non-medically-accepted uses such as athletic enhancement or anti-aging is a federal felony under 21 USC 333(e), which makes it legally distinct from the rest of this class. Prohibited in sport under WADA S2.

• Molitch et al., Endocrine Society clinical practice guideline on adult growth hormone deficiency (guideline)
• Genotropin and Norditropin FDA prescribing information (label)
• Takala et al. 1999 NEJM, increased mortality with high-dose growth hormone in critically ill adults (trial)
• Liu et al. 2007 Annals of Internal Medicine, systematic review of growth hormone in healthy elderly (review)

The sequence above was retrieved directly from UniProt P01241 - the mature chain, residues 27 to 217 of the precursor, 191 amino acids. The receptor mechanism is more interesting than the usual summary suggests. A single GH molecule has two distinct receptor-binding surfaces, site 1 with high affinity and site 2 with lower affinity, and it binds one receptor through site 1 and then recruits a second through site 2. The productive event is not binding but the rotational realignment of a pre-formed receptor dimer, which brings the two associated JAK2 molecules into position to transphosphorylate each other. JAK2 then phosphorylates STAT5b, which dimerises, translocates to the nucleus and drives IGF1 transcription. This two-site requirement is why pegvisomant works: mutate site 2 and you get occupancy without signalling. It is also why very high GH concentrations can theoretically self-inhibit by saturating site 1 on separate receptors. The clinically decisive point is that somatropin bypasses the pituitary entirely. There is no somatostatin brake and no IGF-1 negative feedback to constrain it, which is what makes it categorically more powerful and more dangerous than every secretagogue in this class - the ceiling that protects a sermorelin user does not exist. Two labelled effects are underappreciated. GH inhibits 11-beta-hydroxysteroid dehydrogenase type 1, the enzyme that regenerates cortisol from cortisone in liver and adipose; starting GH therefore reduces local cortisol availability and can unmask a previously compensated central adrenal insufficiency. New fatigue, nausea, dizziness or hypotension after starting GH is a cortisol question until proven otherwise. Second, GH increases peripheral T4 to T3 conversion and can reveal marginal thyroid reserve. Both of these are why GH replacement in hypopituitarism is done with the rest of the axis checked first, and both apply to off-label users who have not thought about it. The Takala trial deserves its own sentence: high-dose GH in 532 critically ill adults roughly doubled in-hospital mortality, 39 versus 20 percent in one arm and 44 versus 18 percent in the other. That is the most important safety finding about GH ever published and it is a permanent reminder that this is a powerful drug, not a supplement.

Escalating too fast. Nearly every miserable GH experience - swollen ankles, hands that will not close, aching joints, numb fingers on waking - is a titration problem, and nearly all of it resolves on a dose reduction that people do not make because they think the side effects mean it is working. Second, adrenal insufficiency. Someone with unrecognised partial hypopituitarism who starts GH can be tipped into an adrenal crisis by the 11-beta-HSD-1 effect, and the presenting symptoms are vague enough to be dismissed. Third, dose units. 1 mg equals 3 IU, and the number of people who have injected 3 mg thinking they were taking 3 IU is not small. Fourth, reconstitution: freezing destroys reconstituted somatropin, shaking aggregates and inactivates the protein, and the difference between a working vial and a dead one is invisible. Roll, never shake. Fifth, the grey-market supply: generic hGH from unregulated sources is one of the most counterfeited products in existence, and the IU labelling on those vials is frequently fictional. Sixth, and specific to the United States, distributing or possessing hGH for athletic enhancement or anti-aging is a federal felony under 21 USC 333(e) - this is not a scheduling technicality, it is a distinct statute that applies to GH and to nothing else in this class.

1. 200 mcgWeeks 1 to 8 — 0.2 mg daily, about 0.6 IU, at bedtime. This is the labelled non-weight-based adult starting dose. Almost every unpleasant GH side effect is a too-fast-escalation problem, and most resolve on a dose reduction.
2. 300 mcgEvery 4 to 8 weeks thereafter — Increase in 0.1 to 0.2 mg steps every one to two months, guided by IGF-1 and symptoms. Slow is not caution here - it is the actual labelled method and it is why clinical GH replacement is generally well tolerated while off-label use often is not.
3. 500 mcgTypical off-label recovery and anti-aging range — 1 to 2 IU daily, which is 0.33 to 0.67 mg. This range mostly keeps IGF-1 within physiological limits and is where side effects stay manageable. Women on oral oestrogen typically need more because first-pass hepatic oestrogen blunts the IGF-1 response; switching to transdermal is usually a better answer than raising the GH dose.
4. 1 mgHigher off-label body-composition range — 3 IU daily. Carpal tunnel, oedema and insulin resistance become common and predictable here, and splitting into two doses reduces peak-related effects. IGF-1 will usually be at or above the top of the range.
5. 2 mgWhere the real risk starts — 6 IU daily and above. This is where acromegalic change stops being theoretical - jaw, brow, hands, and organ growth over years, largely irreversible. Nothing about the cosmetic or performance case justifies it, and this is also the range where the US federal statute on non-medical hGH distribution becomes a live issue rather than an abstraction.

• Growth hormone receptor (GHR), site 1 and site 2 — Site 1 high affinity, site 2 lower affinity; sequential binding is required for productive signalling

  Rotational realignment of a pre-formed receptor dimer, JAK2 transphosphorylation, STAT5b phosphorylation and nuclear translocation, IGF1 transcription.

• Hepatic IGF-1 production — Not applicable

  The main anabolic and growth-promoting arm. Most of the growth effect is IGF-1-mediated rather than direct.

• Adipocyte GH receptor — Not applicable

  Direct lipolysis, independent of IGF-1. This is why GH reduces fat mass even at doses where IGF-1 barely moves.

• Skeletal muscle and hepatic insulin signalling — Not applicable

  Direct counter-regulatory effect. Reduced glucose uptake, increased hepatic glucose output, insulin resistance. Not a side effect but a core action of the hormone.

• 11-beta-hydroxysteroid dehydrogenase type 1 — Inhibited

  Reduced regeneration of cortisol from cortisone in liver and adipose. Unmasks compensated central adrenal insufficiency and can require an increase in oral cortisone doses. A labelled warning.

• Peripheral deiodinase activity — Not applicable

  Increased T4 to T3 conversion, which can unmask central hypothyroidism.

• Cytochrome P450 enzymes — Suppressed

  GH can reduce CYP-mediated drug metabolism. Relevant for narrow-therapeutic-index drugs and specifically flagged in GH labels.

• Takala et al., two parallel randomised placebo-controlled trials of high-dose growth hormone in critically ill adults 3 · n=532 · 1999

  In-hospital mortality. Mortality was substantially higher on GH: 39 percent versus 20 percent in the Finnish trial (247 patients) and 44 percent versus 18 percent in the multinational trial (285 patients), both p less than 0.001. The most important safety finding ever published about growth hormone.

• Liu et al., systematic review of the safety and efficacy of growth hormone in the healthy elderly meta-analysis · n=220 · 2007

  Across 18 study populations, GH reduced fat mass by approximately 2.1 kg and increased lean mass by approximately 2.1 kg, with increased rates of oedema, arthralgia, carpal tunnel syndrome and diabetes. The authors concluded GH cannot be recommended as an anti-aging therapy. This is the definitive answer to the anti-aging question and it is not favourable.

Fluid retention and fat loss begin within two to four weeks and are usually the first things noticed. Improved sleep and skin changes are reported early and are hard to separate from expectation. IGF-1 responds within days to weeks and should be measured at six to eight weeks after any dose change. Body composition changes accrue over three to six months; connective tissue and tendon changes are slower still. Carpal tunnel and arthralgia, when they appear, arrive during escalation and resolve within one to two weeks of a dose reduction. Acromegalic skeletal change requires years of supraphysiological dosing and does not reverse. After stopping, the endogenous axis takes weeks to recover and IGF-1 falls over one to two weeks.

Somatropin conflicts with almost everything else in this class rather than combining with it. Every secretagogue - ipamorelin, CJC-1295 in either form, sermorelin, tesamorelin, MK-677, the GHRPs - works by asking your pituitary to release GH, and exogenous GH suppresses the pituitary through IGF-1 feedback. Running both is paying for one. Somapacitan, lonapegsomatropin and somatrogon are somatropin delivered weekly; they substitute for it, not add to it. Pegvisomant is its direct pharmacological opposite. The combinations that actually matter are the endocrine ones. Insulin requirements rise substantially and diabetics need active management, not a warning. Oral oestrogen markedly blunts the IGF-1 response through a first-pass hepatic mechanism, so women on oral oestradiol need higher GH doses or, better, a switch to transdermal. Supraphysiological glucocorticoids blunt the growth effect, and simultaneously GH's suppression of 11-beta-HSD-1 means oral cortisone doses may need increasing - the interaction runs both ways. Thyroid replacement often needs adjusting upward after starting GH. The single most important practical point is that somatropin is the one compound in this class where the interactions can put someone in hospital.

Somatropin is the reference standard and everything else in this class is measured against it. Against every secretagogue: GH is more powerful because it bypasses the pituitary, and more dangerous for exactly the same reason. A secretagogue cannot produce acromegaly; GH can. Against somapacitan, lonapegsomatropin and somatrogon: those are somatropin with half-life extension, offering one injection a week instead of seven at the price of higher cost, and in the lonapegsomatropin case the molecule released is unmodified somatropin so tissue distribution is unchanged. Against the honest question of whether a healthy adult should use it: Liu's systematic review is the answer. About 2 kg of fat lost and 2 kg of lean gained, with more oedema, arthralgia, carpal tunnel and diabetes, and no functional or longevity benefit demonstrated. That is a real effect and a real cost, and anyone deciding should be looking at those numbers rather than at a transformation photograph.

$150–$3000/month. The spread is real. Pharmacy-supplied branded somatropin in the US at 2 IU daily runs well into the hundreds or low thousands of dollars a month at cash price, with pen devices at the top end. Grey-market generic hGH, typically sold in 100 IU kits, works out around 150 to 400 USD a month at the same dose - and is also one of the most counterfeited products on the market. In much of Asia and Eastern Europe pharmacy pricing sits between the two. Figures are approximate and vary enormously by jurisdiction and source.

• ?Absolute subcutaneous bioavailability is stated as unknown in the Norditropin label and differs between products in any case.
• ?Pharmacokinetic parameters vary substantially between brands and formulations; the figures here are Norditropin's and should not be assumed to transfer.
• ?Whether low-dose GH in healthy adults has any effect on healthspan or longevity is unknown, and the animal literature points in the opposite direction - reduced GH signalling extends lifespan in multiple models.
• ?The long-term cancer risk of sustained IGF-1 elevation in healthy adults is not quantified. The epidemiological association between high-normal IGF-1 and several cancers is consistent but observational.
• ?Grey-market hGH identity and potency are unverifiable without independent assay, and IU labelling on unregulated kits is frequently wrong.
• ?The threshold dose and duration above which acromegalic change becomes irreversible is not defined; the 6 IU daily figure is a practitioner convention rather than a studied boundary.

• Increased mortality associated with growth hormone treatment in critically ill adults Takala J, Ruokonen E, Webster NR, Nielsen MS, Zandstra DF, Vundelinckx G, Hinds CJ, New England Journal of Medicine, 1999 · PMID 10477776

  The reason acute critical illness is an absolute contraindication on every GH label. Also the clearest demonstration that GH is a drug with the capacity to kill people, not a wellness product.

• Systematic review: the safety and efficacy of growth hormone in the healthy elderly Liu H, Bravata DM, Olkin I, Nayak S, Roberts B, Garber AM, Hoffman AR, Annals of Internal Medicine, 2007 · PMID 17227934

  The best synthesis of what GH actually does in healthy older adults: about 2 kg of fat lost, about 2 kg of lean mass gained, more oedema, arthralgia, carpal tunnel and diabetes, and no recommendation for anti-aging use.

• Evaluation and treatment of adult growth hormone deficiency: an Endocrine Society clinical practice guideline Molitch ME, Clemmons DR, Malozowski S, Merriam GR, Vance ML, Journal of Clinical Endocrinology and Metabolism, 2011 · PMID 21602453

  The clinical standard for diagnosis, dosing, IGF-1 targeting and monitoring in adults. If you are going to run GH, this is the document describing how it is done properly.

• NORDITROPIN (somatropin) injection, solution - US prescribing information DailyMed, Novo Nordisk

  Source of the pharmacokinetic figures here: tmax around 3 hours subcutaneously in healthy subjects and 4 to 5 hours in GHD patients, terminal half-life 7 to 10 hours subcutaneously in GHD and about 21 minutes intravenously, volume of distribution 43.9 L, clearance 2.3 mL/min/kg, and the explicit statement that absolute subcutaneous bioavailability is not known.

• UniProtKB P01241, somatotropin (human growth hormone) UniProt Knowledgebase

  Primary sequence source for the 191-residue mature chain given above.