IGF-1 is an anabolic peptide commonly used by bodybuilders to increase metabolism, promote protein synthesis, and help bodybuilders gain muscle mass. So, obviously, IGF-1 makes you bigger. Not only that, IGF-1 has been shown to stimulate testosterone production in testicular interstitial cells and, together with testosterone, mediate some of the growth-promoting effects of androgens in androgen-reactive tissues. So, in addition to building muscle, IGF-1 really does make you bigger.
Effects of testosterone and IGF-1 on anabolic reaction of foreskin fibroblasts
In the experiment, the culture was exposed to increased concentrations of IGF-1, or to increased concentrations of testosterone in the presence and absence of IGF-1, and the protein synthesis response was measured.
Protein synthesis increased dose-dependent as IGF-1 concentrations increased between 25 and 100ng/mL. Compared with the control, the maximum increase was 34+/-3%, P< 0.001.
In contrast, testosterone concentrations increased between 1 and 1000nm, and in the absence of IGF-1, the results did not change.
However, if 50ng/ml of IGF-1 is also present, the response to testosterone is easily detected, and the increased testosterone concentration stimulates protein synthesis, 25-57% higher than the value obtained with testosterone alone.
Results obtained with 10-1000nm testosterone concentration plus IGF-1 were compared with values obtained with 1nm testosterone concentration plus IGF-1, and these concentrations caused more significant increases, P< 0.05.
Illustrated position
The figure on the left above shows the protein synthesis response of the hypertrophic organism to IGF-1+ testosterone. With increasing IGF-1 concentration, protein synthesis increased in a dose-dependent manner. The figure on the right above shows the protein synthesis reaction with increasing testosterone concentration in the presence (•) or absence of (○) IGF-I (50 ng/mL).
This study clearly shows that there is an interaction between testosterone and IGF-1 that stimulates total protein synthesis in fibroblasts. If IGF-1 is not added, even if the testosterone concentration is increased to 1000nm, there is no effect on the protein synthesis response of these cells. If IGF-1 is added, even if the testosterone concentration is as low as 10nm, it will stimulate protein synthesis.
At the same time, the synergistic effect of testosterone and IGF-1 can also be seen by comparing the left and right figures in the accompanying figure: testosterone enhances the maximum effect that IGF-1 can obtain.
Therefore, in addition to increasing muscle, the anabolic effects of IGF-1 also help to improve the effect of testosterone, especially in androgenic tissues.

Description of IGF-1
IGF-1, short for insulin-like growth factor 1, is very similar in molecular structure to insulin, is produced primarily in the liver, and has anabolic effects in adults.
In addition to acting as IGF-1, IGF-1 supplementation stimulates endogenous IGF-1 production in the corresponding tissues. IGF-1 has a growth-promoting effect on almost every cell, especially skeletal muscle, cartilage, bone, liver, kidney, nerve, skin, etc. It promotes cell enlargement and division, inhibits apoptosis and increases cellular protein synthesis, coordinating the metabolism of proteins, carbohydrates and fats.
Treatment of primary IGF-1 deficiency with IGF-1
The FDA approved the use of rhIGF-1(also known as Mecasermin) for the treatment of severe primary IGF-1 deficiency in 2023. At the same time, the FDA approved the use of an equal molar combination of IGF-1 and IGFBP-3 (also known as Mecasermin Rinfabate) for the treatment of IGF-1 deficiency. Because IGFBP-3 also carries IGF-1, the carrier IGFBP-3 is saturated with IGF-1 when IGF-1 is administered alone, and IGF-2 can be bypassed to bind to IGF-1 when an equimolar combination of IGF-1 and IGFBP-3 is used. Both of these combined modes can be used to treat growth disorders.
IGF-1 is used to treat muscle injuries
The patented drug PEG-IGF-1 is an analogue of IGF-1, which provides effective protection against muscle damage caused by targeted acute contractions. It is also used to treat and prevent neuromuscular disorders, especially amyotrophic lateral sclerosis.
IGF-1 for burns
In Phase II trials of IGF-1, the efficacy of IGF-1 in the treatment of severe burns in children was demonstrated and positive results were achieved at doses of 1-4mg/kg/day.
IGF-1 is used to treat osteopenia and osteoporosis
IGF-1 has been tested in patients with osteopenia and osteoporosis associated with anorexia nervosa and severe fractures at doses ranging from 30 µg to 1 mg/kg/ day for 2-9 months with positive results.
IGF-1 is a hormone that exists in almost all human tissues. It is mainly produced by GH stimulation, and it is also an autocrine hormone. In addition, supplementing exogenous IGF-1 can also stimulate the secretion of IGF-1 in body tissues.

IGF-1, stimulated by GH, is synthesized and secreted in the liver, and is also produced in target tissues in both autocrine and paracrine modes. How does IGF-1 play its anabolic role?
IGF-1 works by binding to the IGF-1 receptor, and before binding to the IGF-1 receptor, IGF-1 is transported to various parts of the body via IGF-binding proteins. Before we can understand how IGF-1 plays an anabolic role, we need to understand the IGF-1 receptor and IGF-binding proteins.
What is the IGF-1 receptor?
The IGF-1 receptor is a protein that exists on the surface of human cells and is activated by the IGF-1 hormone, thereby exerting anabolic effects.
IGF-1, which stands for insulin-like growth factor 1, has a similar molecular structure to insulin and therefore also binds to insulin receptors. However, its binding affinity with IGF-1 receptor is much higher than that with insulin receptor, so IGF-1 mainly binds to IGF-1 receptor and produces corresponding effects.
What are IGF-binding proteins?
Igf-binding protein is also known as IGFBP. IGF-1 has been shown to bind and interact with all seven IGFBPs (IGFBP1, IGFBP2, IGFBP3, IGFBP4, IGFBP5, IGFBP6, IGFBP7). In the human body, 99% of IGFs bind to a series of binding proteins and are then carried to various parts of the body to bind to IGF-1 receptors at various sites, thereby exerting their anabolic effects.
The availability of IGF-1 is regulated by IGFBP, and by binding to IGFBP, the half-life of IGF-1 can be extended from a few minutes to a few hours to function. Different IGFBPs can also guide IGF-1 to different tissues and bind to specific IGF-1 receptors, thereby exerting corresponding effects.
Anabolic effects of IGF-1
Almost all IGF-1 binding to IGFBP is transported to various parts of the body, binds to the corresponding IGF-1 receptors and plays anabolic roles, contributing to tissue growth and development, proliferation, lipid metabolism, pro-survival, anti-aging, anti-aging and anti-oxidation, and nerve and liver protection. The antioxidant effects of IGF-1 protect mitochondria from oxidative damage and increase ATP synthesis, providing the body with energy and motivation for exercise.

Through the medical value of IGF-1, we know that the role of IGF-1 includes promoting growth and development, inhibiting muscle atrophy, promoting muscle growth, and benefiting bone health. In addition to these effects, IGF-1 also has anti-aging, anti-oxidation, enhanced immunity, improved learning ability, and regulated lipid metabolism and carbohydrate metabolism.
IGF-1 and lipid metabolism
A study of eight GH-deficient subjects showed that IGF-1 administration increased lipid oxidation, energy expenditure, and insulin resistance. This effect is thought to be due to IGF-1 inhibiting insulin secretion, which leads to enhanced lipidolysis in adipose tissue and promotes muscle utilization of free fatty acids.
Although mature fat cells are not the target of IGF-1, high concentrations of IGF-1 promote the secretion of IGF-1 by fat cells, and IGF-1 is involved in lipid metabolism through its interaction with insulin receptors.
IGF-1 and carbohydrate metabolism
IGF-1 has a direct effect on muscle glucose uptake, and a large number of IGF-1 receptors are present in skeletal muscle.
IGF-1 promotes peripheral tissue glucose uptake by 4%-7% more than insulin.
Anti-inflammatory effects of IGF-1
The fat tissue of obese people produces pro-inflammatory cytokines that interfere with normal nutritional signaling, leading to metabolic syndrome. The anti-inflammatory effects of IGF-1 may protect tissues in chronic diseases such as obesity from the harmful effects of pro-inflammatory factors.
IGF-1 anti-aging
Long filling of telomeres in DNA has been shown to be an important factor in longevity, and levels of IGF-1 are associated with longer telomere length in healthy subjects of all ages and in older men.
Antioxidant
IGF-1 increases glutathione peroxidase, an important antioxidant enzyme that protects cells by preventing cell death and increasing antioxidant status. It produces antioxidant effects that protect mitochondria from oxidative damage and increase ATP synthesis, providing the body with energy and motivation for movement.
Bone mineral density
IGF-1 is a direct promoter of bone growth. In older women, higher levels of IGF-1 are associated with higher bone mineral density. The anabolic effects of IGF-1 also promote bone density, and more muscle mass requires greater bone strength to support it.
Neuroprotective effect of IGF-1
Circulating IGF-1 has important vascular protective properties. Since cerebrovascular changes have a clear role in cognitive decline, reduced IGF-1 levels in aging populations may lead to vascular complications that lead to cognitive dysfunction.

IGF-1 is a naturally occurring anabolic hormone, and growth hormone (HGH) also acts through IGF-1. The two commonly used hormones associated with IGF-1 are IGF-1 LR3 and des(1-3)IGF-1, and to understand the relationship between these three, we also need to understand another hormone associated with IGF-1, IGFBP.
IGF-1
IGF-1, short for insulin-like growth factor 1, also known as growth regulator C, is a hormone with a molecular structure similar to insulin.
IGF-1 is a protein encoded by the IGF1 gene in humans. IGF-1 consists of 70 amino acids on a single chain. It is produced primarily by the liver as an endocrine hormone and is produced in target tissues in a paracrine/autocrine manner.
IGF-1 has been shown to bind and interact with all seven IGF-1 binding proteins (IGFBP) : IGFBP1, IGFBP2, IGFBP3, IGFBP4, IGFBP5, IGFBP6, and IGFBP7.
Here comes IGFBP, which has a high binding affinity with IGF-1 and IGF-2, which prevents IGF-1 from binding to the IGF-1 receptor and functioning. IGFBP is naturally occurring in the body and greatly affects the potency of GIF-1. This is about one of the main reasons for the emergence of IGF-1 LR3 and des(1-3)IGF-1.
IGF-1 LR3
Also known as long arginine 3-IGF-1 or LR3-IGF-1. Is a synthetic protein due to the lengthening analogue of IGF-1.
Elimination half-life: 56-72 hours
Cas:143045-27-6
MF:C400H625N111O115S9
MW: 9117.60
It differs from natural IGF-1 in that it has arginine instead of glutamate in the third position of its amino acid sequence, and also has an additional 13 amino acids in the amino acid sequence. N-terminal, a total of 83 amino acids (IGF-1 is 70). The result of these modifications is that IGF-1 LR3 retains the pharmacological activity of IGF-1 as an IGF-1 receptor hormone agent, has a very low affinity for insulin-like growth factor binding protein (IGFBP), and improves metabolic stability.
As a result, IGF-1 LR3 is about three times more potent than IGF-1 and has a significantly longer half-life of about 20-30 hours (IGF-1 has a half-life of about 12-15 hours).
DES(1-3)IGF-1
It is a naturally occurring endogenous protein and a truncated analogue of drugs and IGF-1. Des(1-3)IGF-1 lacks the first 3 amino acids of the IGF-1N terminal (67 amino acids in total, compared to 70 amino acids of IGF-1). Because of this difference, it greatly reduces binding to IGFBP and increases potency (in vivo about 10 to IGF-1).
Cas:112603-35-7
MF:C319H501N91O96S7
MW: 7371.48
As can be seen from IGF-1 LR3 and des(1-3)IGF-1, both were developed primarily to reduce their binding to IGFBP and thus increase their potency. So we often see the sale of IGF-1 LR3 and des(1-3)IGF-1 peptides, but we rarely see direct IGF-1.