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Hormones & growth

HGH 191AA (Somatropin)

Recombinant human growth hormone with the full 191 amino acid sequence, the best studied and at the same time most overhyped item in the scene.

3 min read 14 sources

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Summary

At a glance

Sources checked on 25 Oct 2026

Chain length
191 amino acids

same sequence as the body's own hormone, according to UniProt (P01241)14

Half-life
~3.2 hours

injected under the skin in healthy adults; back to baseline after 20 to 22 hours8

Lean mass in older adults
+2.1 kg

review of 18 study populations, fat mass -2.1 kg, weight unchanged2

Sprint capacity
+3.9 %

young recreational athletes after 8 weeks, gone again 6 weeks after stopping6

Joint pain
41 %

older men on growth hormone over 26 weeks (placebo 0%)4

  • HGH 191AA is recombinant somatropin: the complete chain of 191 amino acids, identical to the growth hormone from the pituitary gland.1411
  • It binds to the growth hormone receptor. The liver then makes IGF-1, which passes on many of the effects. Growth hormone also releases fat and works against insulin.109
  • In healthy older adults lean mass rose by 2.1 kg on average in trials and fat mass fell by 2.1 kg. Strength and endurance did not measurably improve.23
  • Water retention, joint pain and carpal tunnel complaints were more common than without growth hormone. Raised blood sugar and diabetes also occurred more often.24
  • As a medicine, somatropin is approved only for specific diagnoses such as growth hormone deficiency, not against ageing. Everything here is the state of research, not a recommendation.132
Profile

Updated May 2026

Class
Recombinant growth hormone

191 AA

Use
Subcutaneous

daily

Half-life
short

IGF-1 effect lasts longer

WADA
Banned

peptide hormones

Sizes
8 to 50 IU

12 sizes in the shop

Contents 16 sections
  1. At a glance
  2. What is HGH 191AA?
  3. How it works
  4. What you need
  5. Mixing and units
  6. Dosing (in IU)
  7. Injection
  8. What the research shows
  9. Research status
  10. Side effects
  11. Practice
  12. Storage
  13. Related compounds
  14. FAQ
  15. Glossary
  16. Sources

What is HGH 191AA?

HGH 191AA is recombinant human growth hormone with the full sequence of 191 amino acids, identical to the body's own somatropin. The 191AA label distinguishes it from older, truncated variants.

Growth hormone is the best studied item in this corner and at the same time the most overhyped. The effects on body composition are real, the functional benefit in healthy people is far smaller than the marketing suggests.

Comparison

Other routes to growth hormone

Where each compound acts, as stated in the TPD lexicon. Tap a card to open its entry.

GHRH analogue Sermorelin GHRH Ghrelin mimetic Ipamorelin Ghrelin Ghrelin receptor agonist, oral MK-677 (Ibutamoren) Ghrelin
The hormone itself HGH 191AA (Somatropin) GH
IGF-1 analogue IGF-1 LR3 IGF-1

How it works

HGH acts partly directly at GH receptors and partly indirectly: it prompts the liver to produce IGF-1, which mediates many of the anabolic and regenerative effects. GH itself also has a fat-mobilizing (lipolytic) action.

The half-life of GH in the blood is short, but the IGF-1-mediated effect lasts longer. That is why you dose low and regularly rather than rarely and high.

Where it acts

One receptor, several organs

Tap a point or a card. Colour = receptor, grey = effect seen in trials.

  1. Pituitary gland

    Makes the body's own growth hormone, less with age. This is seen as one reason for less lean mass and more fat1

    Observed in trials
  2. Muscle

    Lean mass rose, in young athletes mainly through more water in the tissue6

    Observed in trials
  3. Liver

    Makes IGF-1 in response, which carries many of the effects10

    GH
  4. Blood sugar

    Works against insulin, insulin resistance increases9

    GH
  5. Fat tissue

    Fat breakdown (lipolysis) rises markedly, more free fatty acids in the blood9

    GH

Targets in the ChEMBL database13

Compound CHEMBL1201621: one recorded mechanism, agonist with direct binding to the human receptor.

Growth hormone receptor
Gene
GHR
UniProt
P10912
ChEMBL
CHEMBL1976
Action
Agonist, direct binding
Glass liver model with blue 3D protein folds, with trails of light leading to muscle fibres and yellow fat cells
Symbolic image.

What you need

Supplies

4 things, numbered as in the picture

Tick off what you already have. Vial and BAC water are our real shop photos at the same size.

HGH vial and bacteriostatic water at the same size with the black TPD label, next to two U-100 insulin syringes, two alcohol swabs and a sharps container with a blue lid

  1. HGH vial

    The HGH vial (lyophilized powder).

    In the shop

  2. Bacteriostatic water

    Bacteriostatic water for mixing.

    In the shop

  3. U-100 insulin syringes

    U-100 insulin syringes for injection.

    Amazon (opens a new tab)

  4. Alcohol swabs

    Alcohol swabs and a clean workspace.

    Amazon (opens a new tab)

As an Amazon associate we earn from qualifying purchases. Links open Amazon - no extra cost for you.

Mixing and units

HGH is given in IU (international units), not in mg. As a rough rule: about 1mg corresponds to roughly 3 IU. Vials are usually labeled with their IU count.

  • Example: dissolving a 10 IU vial with 1ml bacteriostatic water gives 10 IU per ml.
  • On a U-100 insulin syringe that is 100 units for the full 10 IU.
  • 2 IU is then 20 units on the syringe, 4 IU is 40 units.

Just add the water, it does not matter if it hits the powder directly. Swirl or shake until dissolved.

Step by step

Dissolving the powder

Four steps, the same for every vial size.

  1. 1Wipe the cap

    Clean the rubber stopper with an alcohol swab.

  2. 2Add BAC water

    Just add it, it does not matter if it hits the powder directly.

  3. 3Swirl or shake

    Until everything has dissolved, both are fine.

  4. 4Draw up

    With the U-100 insulin syringe.

Less water higher concentration fewer units on the syringe Example: 10 iu + 1 ml = 10 iu/ml

Dosing (in IU)

Dosing

Dosing, titration and syringe

Loading the dosing information …

  • Getting started and stepping up, drawn as a staircase
  • Units on the U-100 syringe for every step
  • How long one vial lasts

Injection

The injection is subcutaneous, into the fat layer under the skin. Common spots are the abdomen (keep about two finger-widths clear of the navel), the front and the inner side of the thigh, or the back of the upper arm. Use the short insulin needle for this.

The short version:

Injection

Where and at what angle

Pick a spot or switch the angle. Subcutaneous means: into the fat layer, not the muscle.

Rotate the spot each time, never the same one twice in a row.

90°More fat under the skin

Rule of thumb: where there is more fat under the skin, insert straight at 90 degrees. In lean people with little fat, 45 degrees, so the needle stays in the fat layer. Simplified diagram.

  1. Clean the spot with an alcohol swab and let it dry

  2. Pinch up a small fold of skin

  3. Insert the needle: at 90 degrees where there is more fat under the skin, at 45 degrees in lean people with little fat

  4. Inject slowly, wait a moment, then withdraw

  5. Put the needle straight into the sharps container

Rotate the site each time so the tissue does not get irritated. Never the same spot twice in a row.

Many dose in the morning fasted, some split into morning and pre-workout.

What the research shows

The classic study (Rudman, 1990) gave men over 60 growth hormone and saw a moderate increase in muscle mass, more bone density and less body fat. This study helped kick off the entire anti-aging hype.

The honest correction came later: a systematic review (Liu, 2007) summarized the studies in healthy older adults and concluded that GH changes body composition slightly but does not improve function and increases the rate of side effects. It could not be recommended as an anti-aging therapy.

Study results

What the trials measured

Interactive: switch tabs, tap points, show or hide arms. Arms are named relative to each other, no dosing advice.

Body composition in older men31

Change in percent after six months, two trials

Lean mass3 52 healthy men over 69, with a placebo group
Placebo -0.1%
Growth hormone +4.3%
Fat mass3 Same trial
Placebo -0.3%
Growth hormone -13.1%
Lean mass (Rudman)1 12 men aged 61 to 81 on growth hormone, no placebo
Growth hormone +8.8%
Adipose tissue (Rudman)1
Growth hormone -14.4%
Lumbar bone density (Rudman)1
Growth hormone +1.6%

In the Rudman study the untreated group showed no significant change, the abstract gives no exact values. In the placebo-controlled trial strength and endurance did not improve despite more lean mass.

Sprint capacity after eight weeks6

Relative difference to placebo, 96 recreational athletes

Sprint (Wingate test)6 Women and men combined, or men with testosterone
Growth hormone, difference to placebo +3.9%
Plus testosterone, difference to placebo (men only) +8.3%

Endurance, strength and jump height did not change significantly. Six weeks after stopping, the sprint advantage was gone. The extra lean mass came mainly from more water in the tissue.

Liver fat after six months7

Absolute change in liver fat fraction in percentage points, 53 adults with overweight and fatty liver (NAFLD)

Liver fat fraction7 Measured by MR spectroscopy
Placebo +3.8 pp
Growth hormone -5.2 pp

Net difference 8.9 percentage points. The trial aimed for IGF-1 in the upper normal range. Blood sugar and insulin resistance did not change significantly compared with placebo.

Glass model of a thigh bone under a glass cover in a bright room
Symbolic image.

Research status

Where the research stands

Registered trials with status, participants and results. As of 25 Oct 2026. 12

  1. Preclinical Recombinant production in bacteria (1979)
  2. Phase 1 1 trial, 1 completed
  3. Phase 2 3 trials, 2 completed
  4. Phase 3 no registered trial
  5. Approval only for specific diagnoses
Approved as a medicine (ChEMBL: highest phase 4), but only for diagnoses such as growth hormone deficiency. Not approved against ageing or for performance.13
Show all 3 phase 2 trials on a timelineHide timeline 2 completed 1 running 1 with results
Phase 2

Bar: start to primary endpoint (planned for running trials). Green = completed, blue = progress until 25 Oct 2026. Phase 1: 1 trial on safety and pharmacokinetics, not shown as bars.

Side effects

  • Water retention, swollen hands, joint stiffness, especially at the start and at higher doses.
  • Carpal-tunnel-type complaints (pinched nerve in the wrist).
  • Worsened insulin sensitivity, rising blood glucose, the central risk at higher doses.
  • Rarely tingling or numbness. Much of this is dose-dependent and reverses when reducing.

Tolerability

Frequency in placebo-controlled trials

Out of 100 participants per group, how many had the event within 26 weeks or six months.

0 of 100 Placebo
41 of 100 Growth hormone
Event PlaceboGrowth hormone
Joint pain (older men)4 0%41%
Oedema (older women)4 0%39%
Dose had to be lowered (older men)3 0%26%
Leg oedema (fatty liver trial)7 0%21%

Values from the abstracts. Carpal tunnel complaints also occurred in 32 percent of older men on growth hormone plus testosterone (placebo 0 percent). Diabetes or impaired glucose tolerance occurred in 18 men with and 7 without growth hormone.437

Practice

  • Start at 2 IU, be patient, GH works over weeks, not days.
  • Keep an eye on blood glucose, especially from 4 IU upward.
  • Keep expectations realistic, the data are more sober than the marketing.
  • Banned in official competition.
Two light blue dumbbells and a salad bowl with egg, broccoli and vegetables on a bright table
Patience, keep an eye on blood sugar, keep expectations realistic. Symbolic image.

Storage

Before mixing the powder is robust, normal room temperature (around 20 to 25 degrees) is fine, ideally kept in the dark. After mixing, keep in the fridge (2 to 8 degrees), do not freeze. It stays good there for at least 2 to 3 months with barely any loss of potency, in practice considerably longer. Swirl or shake to mix, both are fine.

Shelf life

How long it keeps

Undissolved (powder) Room temperature, around 20 to 25 degrees, dark

Robust, no fridge needed.

Dissolved (mixed) Fridge, 2 to 8 degrees, do not freeze

At least 2 to 3 months with barely any loss of potency, in practice considerably longer.

  • Keep it dark
  • Dissolved: 2 to 8 degrees
  • Note the mixing date on the vial
Nine vials with white powder and blue caps in the door shelf of a bright fridge
Powder dark at room temperature, once dissolved into the fridge (2 to 8 degrees), do not freeze. Stable there for at least 2 to 3 months. Symbolic image.

Related

Related compounds

A different path: all in the TPD lexicon.

HGH 191AA (Somatropin)
Tesamorelin GHRH path: stimulates the body's own release Sermorelin GHRH path, short chain (1-29) CJC-1295 with DAC GHRH path, long-acting CJC-1295 without DAC GHRH path, short-acting Ipamorelin Ghrelin path, selective GHRP-2 Ghrelin path MK-677 (Ibutamoren) Ghrelin path, studied as a tablet CP10 (CJC + IPA) GHRH plus ghrelin path IGF-1 LR3 Downstream: the messenger IGF-1 HGH Fragment 176-191 Fragment of HGH (amino acids 176 to 191)

FAQ

Common questions about HGH 191AA (Somatropin)

Short answers, each backed by the sources below.

What does 191AA mean?

191AA stands for 191 amino acids. That is the length of the human growth hormone chain after the body removes the signal piece at the start. HGH 191AA has exactly this sequence. It is made by genetic engineering, which first succeeded in bacteria in 1979.1411

Is somatropin approved?

Yes, but only for specific diagnoses. ChEMBL lists somatropin as an approved medicine, for example for growth hormone deficiency, Turner syndrome, Prader-Willi syndrome or short bowel syndrome. It is not approved against ageing. A 2007 review concluded that it cannot be recommended for that.132

What did the Rudman study show?

21 healthy men aged 61 to 81 with low IGF-1, 12 of them received growth hormone for six months. In this group lean mass rose by 8.8 percent, adipose tissue fell by 14.4 percent and lumbar bone density rose by 1.6 percent. The untreated group showed no significant change. There was no placebo group.1

Does growth hormone make you stronger?

Barely, in the trials. In 52 older men lean mass rose by 4.3 percent, but strength and endurance did not improve. A review of young, fit people (303 on growth hormone) found 2.1 kg more lean mass, but no better strength or exercise capacity. In recreational athletes only sprint capacity rose, by 3.9 percent.356

How long does HGH stay in the blood?

Not long. Injected under the skin, the half-life in healthy adults was about 3.2 hours. After 20 to 22 hours the level was back at baseline. Many effects, however, run through IGF-1, which the liver makes in response.810

Which side effects were seen?

In the review of healthy older adults water retention (oedema), joint pain, carpal tunnel syndrome and enlarged breast tissue in men (gynaecomastia) were clearly more common. Diabetes and raised fasting glucose occurred somewhat more often. In a trial with 131 older women and men, 41 percent of the men on growth hormone had joint pain. 39 percent of the women developed oedema.24

What happens to blood sugar?

Growth hormone works against insulin and can cause insulin resistance. In a trial with older adults 18 men on growth hormone developed diabetes or impaired glucose tolerance, versus 7 without growth hormone. In a low-dose trial in fatty liver, by contrast, blood sugar and insulin resistance did not change measurably.947

What happens to liver fat?

In a trial with 53 adults with overweight and fatty liver (NAFLD) the liver fat fraction fell by 5.2 percentage points in six months, on placebo it rose by 3.8. That makes a difference of 8.9 percentage points. Leg oedema was more common on growth hormone (21 versus 0 percent).7

Which trials are still running?

There are only a few entries on growth hormone in healthy older adults on ClinicalTrials.gov. One phase 2 trial on the ageing immune system (TRIIM-X), which combines growth hormone with two further agents, is still listed as recruiting. Its entry was last updated in May 2025 (as of 25 October 2026).12

Glossary

Terms explained briefly

Dotted words in the text open these explanations directly.

Amino acid
Building block of proteins. Growth hormone is a chain of 191 of them.
Bone density
Mineral content of bone, a measure of its strength.
Carpal tunnel syndrome
Compressed nerve in the wrist. Typical are tingling, numbness and pain in the fingers.
Half-life
Time after which only half of a substance is left in the blood. For growth hormone under the skin this is only a few hours.
IGF-1
Insulin-like growth factor 1. The liver makes it in response to growth hormone. It carries many of the anabolic effects.
Insulin resistance
Cells respond less to insulin, so blood sugar rises more easily. Growth hormone can make this worse.
IU
International unit. Growth hormone is traditionally given in IU rather than milligrams.
Lean mass
Everything in the body except fat: muscle, organs, bone and water. If it rises, that is not automatically just muscle.
Lipolysis
Breakdown of stored fat into free fatty acids that enter the blood.
Lyophilisate
Freeze-dried powder. Without water a protein keeps much longer.
NAFLD
Non-alcoholic fatty liver disease, today mostly called MASLD.
Oedema
Fluid build-up in the tissue, for example in the hands or legs.
Placebo
Dummy preparation without active substance. Comparing against it shows what is due to the substance itself.
Receptor
Protein on the cell surface that a messenger docks onto. Only then does the cell respond.
Recombinant
Made by genetic engineering: cells receive the blueprint of the protein and then make it themselves.
Somatropin
Technical name for human growth hormone, as the body makes it or as it is produced by genetic engineering.
Subcutaneous
Into the fat layer just under the skin.
Systematic review
A paper that finds and summarises all suitable studies on a question according to fixed rules.

Evidence

Sources

Show all 14 sourcesHide sources 11 Studies1 Trial registry2 Database checked 25 Oct 2026

Studies

  1. Growth hormone in men over 60 (Rudman study)

    Rudman et al., New England Journal of Medicine, 1990

    DOI 10.1056/NEJM199007053230101 PMID 2355952
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed
  2. Systematic review in healthy older adults

    Liu et al., Annals of Internal Medicine, 2007

    DOI 10.7326/0003-4819-146-2-200701160-00005 PMID 17227934
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed
  3. Placebo-controlled trial in healthy older men

    Papadakis et al., Annals of Internal Medicine, 1996

    DOI 10.7326/0003-4819-124-8-199604150-00002 PMID 8633830
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed
  4. Placebo-controlled trial in older women and men

    Blackman et al., JAMA, 2002

    DOI 10.1001/jama.288.18.2282 PMID 12425705
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed
  5. Systematic review on athletic performance

    Liu et al., Annals of Internal Medicine, 2008

    DOI 10.7326/0003-4819-148-10-200805200-00215 PMID 18347346
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed
  6. Placebo-controlled trial in recreational athletes

    Meinhardt et al., Annals of Internal Medicine, 2010

    DOI 10.7326/0003-4819-152-9-201005040-00007 PMID 20439575
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed
  7. Placebo-controlled trial in fatty liver with overweight

    Dichtel et al., Journal of Clinical Endocrinology & Metabolism, 2023

    DOI 10.1210/clinem/dgad375 PMID 37379033 NCT02217345
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed, Europe PMC
  8. Pharmacokinetics in healthy adults and dialysis

    Langbakke et al., Clinical Endocrinology, 2007

    DOI 10.1111/j.1365-2265.2007.02962.x PMID 17634080
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed
  9. Review: glucose, fat and protein metabolism

    Møller und Jørgensen, Endocrine Reviews, 2009

    DOI 10.1210/er.2008-0027 PMID 19240267
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed
  10. Review: the growth hormone receptor

    Brooks und Waters, Nature Reviews Endocrinology, 2010

    DOI 10.1038/nrendo.2010.123 PMID 20664532
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed
  11. First recombinant production in bacteria

    Goeddel et al., Nature, 1979

    DOI 10.1038/281544a0 PMID 386136
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed

Trial registry

  1. Trials on ClinicalTrials.gov

    ClinicalTrials.gov, U.S. National Library of Medicine

    Checked 25 Oct 2026 via ClinicalTrials.gov API v2

Database

  1. Mechanism, target and approvals in ChEMBL

    ChEMBL, EMBL-EBI (CHEMBL1201621)

    Checked 25 Oct 2026 via ChEMBL
  2. Growth hormone sequence in UniProt

    UniProt, Eintrag P01241 (GH1)

    Checked 25 Oct 2026 via UniProt

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