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Insulin research

What published studies found for Insulin: 8 papers, 2 in humans, with sample sizes and key results.

B
Some human evidence
Why: Approved for diabetes, but for muscle building only small controlled infusion studies exist, showing reduced protein breakdown rather than growth.

Insulin is an essential diabetes drug, but its off-label use by non-diabetic bodybuilders to build muscle has no controlled human evidence of benefit; human physiology studies show insulin mainly slows muscle protein breakdown and is anabolic only when amino acids are supplied. The published literature on non-medical use consists of case reports of severe, sometimes refractory hypoglycaemia and reviews warning of the risks.

✗ 5 negative? 3 inconclusive

No controlled trials have tested insulin for muscle gain in healthy people; harms in non-diabetics come from case reports, and hypoglycaemia can be prolonged and refractory to treatment.

US compounding: Approved biologic: not compoundable. Insulins are FDA-approved biologics; biologics can't be compounded from bulk under section 503A. Status for every peptide.

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Reported side effects

Human studies

? Inconclusivehuman trialAm J Physiol Endocrinol Metab · 2006

Mechanism of insulin's anabolic effect on muscle: measurements of muscle protein synthesis and breakdown using aminoacyl-tRNA and other surrogate measures.

n = 18 humansTracer infusion study with femoral arterial insulin vs saline infusion4-hour insulin infusion

In 18 healthy adults, a 4-hour leg insulin infusion reduced muscle protein breakdown by about 28% but did not stimulate muscle protein synthesis vs saline.

Key resultInsulin reduced muscle protein breakdown (leucyl-tRNA based -28%; P < 0.02) with no significant effect on muscle protein synthesis
Studied
Healthy adults studied postabsorptive
Compared with
Saline
Main outcome
Muscle protein breakdown and synthesis (leucine/phenylalanine kinetics, aminoacyl-tRNA precursor)
Sample
18 healthy subjects (10 insulin, 8 saline)
Authors' conclusion
In healthy postabsorptive humans insulin does not stimulate muscle protein synthesis; it achieves muscle protein anabolism by inhibiting muscle protein breakdown.
Limitations
Small study of healthy, postabsorptive subjects; local arterial infusion.
PubMed 16705065DOI
? Inconclusivehuman trialFASEB J · 2006

Insulin resistance of muscle protein metabolism in aging.

Young (25+/-2 y) and older (68+/-1 y) healthy subjects; group sizes not statedHyperinsulinemia with stable isotope tracer techniques, young vs old

Hyperinsulinaemia in healthy young and older adults improved leg protein balance and raised muscle protein synthesis only in the young, an effect tied to increased amino acid delivery and blood flow.

Key resultMuscle protein synthesis increased only in the young during hyperinsulinemia; changes in synthesis correlated with leg amino acid delivery (R=0.89; P=0.0001) and blood flow (R=0.90; P<0.0001)
Studied
Healthy young (25+/-2 years) and older (68+/-1 years) subjects
Compared with
Young vs older subjects
Main outcome
Muscle protein synthesis and breakdown, leg phenylalanine net balance
Authors' conclusion
Skeletal muscle protein synthesis is resistant to the anabolic action of insulin in older subjects, which may contribute to the development of sarcopenia.
PubMed 16464955DOIFree full text

Reviews

? InconclusivereviewBaillieres Clin Endocrinol Metab · 1993

Insulin action on protein metabolism.

No new dataNarrative review

Review of insulin and protein metabolism: without an accompanying amino acid supply insulin is not anabolic in muscle; net protein gain occurs only when amino acids are maintained, as after a mixed meal.

Authors' conclusion
With reduced amino acid availability insulin is not anabolic in muscle; if amino acids are maintained at normal or high levels, as after a mixed meal, net muscle protein deposition may occur.
Limitations
Narrative review with no original data.
PubMed 8304920DOI
✗ NegativereviewBr J Pharmacol · 2008

Growth hormone, IGF-I and insulin and their abuse in sport.

No new dataNarrative review

Review of GH, IGF-I and insulin abuse in sport: athletes self-administering large doses expose themselves to harm, including profound hypoglycaemia; testing for insulin misuse was still developing.

Authors' conclusion
Athletes self-administering large doses of GH, IGF-I and insulin expose themselves to potential harm, including profound hypoglycaemia; testing for IGF-I and insulin is in its infancy.
Limitations
Narrative review with no original data.
PubMed 18376417DOIFree full text
✗ NegativereviewEndocr Rev · 2014

Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement.

No new dataEndocrine Society scientific statement (narrative synthesis)

Endocrine Society statement: performance-enhancing drug use, mostly by non-athlete weightlifters, is linked to increased risk of death and many cardiovascular, metabolic, psychiatric and other disorders, and is often combined with other drugs.

Authors' conclusion
Performance-enhancing drug use has been linked to increased risk of death and a wide variety of cardiovascular, psychiatric, metabolic and other disorders; observational studies are needed to collect valid outcome data.
Limitations
Review/statement; randomized trials cannot ethically duplicate real-world PED doses.
PubMed 24423981DOIFree full text

Human studies

✗ Negativecase reportJ Emerg Med · 2019

Severe Hypoglycemia Due to Cryptic Insulin Use in a Bodybuilder.

Single caseCase report

A 30-year-old bodybuilder presented in coma from severe hypoglycaemia requiring repeated glucose infusions, later traced to covert insulin injections taken as a muscle-building aid.

Studied
30-year-old male bodybuilder
Authors' conclusion
Emergency physicians should consider exogenous insulin as an ergogenic aid in bodybuilders presenting with decreased consciousness and treatment-refractory hypoglycemia.
Limitations
Single case report.
PubMed 30527564DOI
✗ Negativecase reportAnasthesiol Intensivmed Notfallmed Schmerzther · 1998

[Insulin as an anabolic: hypoglycemia in the bodybuilding world].

Single case (30-year-old male)Case report

A 30-year-old bodybuilder injected short-acting insulin before a competition to stimulate growth hormone and developed severe hypoglycaemia with loss of consciousness and convulsions, requiring intubation, glucose and glucagon in intensive care.

Studied
30-year-old male bodybuilder who injected 70 IE of short-acting insulin
Authors' conclusion
In any case of severe hypoglycaemia, repeated blood glucose measurement, even prehospital, should be performed, especially if athletes are concerned.
Limitations
Single case report.
PubMed 9728265DOI
✗ Negativecase reportJ Med Assoc Thai · 2008

Attempted suicide by massive insulin injection: a case report and review of the literature.

Single case (80-year-old man)Case report with literature reviewIntravenous dextrose required for 13 days

A non-diabetic man who injected massive doses of insulin needed intravenous dextrose for 13 days and developed low sodium, potassium and phosphate and raised liver enzymes before recovering.

Studied
80-year-old non-diabetic man who injected 10,000 units Humulin R and 6000 units Humulin N
Authors' conclusion
He recovered completely without complication after careful blood glucose monitoring and titration of intravenous glucose over about two weeks.
Limitations
Single case report.
PubMed 19133531

Verdicts are judged on each paper's own main outcome; grades run from A (strong human evidence) to D (little or none). Details are read from the abstracts, and figures are reproduced only from openly licensed full texts. Not medical advice.