IGF-1 LR3 Explained

In this article, we will take a close look at IGF-1 LR3, a synthetic analog of Insulin-like Growth Factor 1 (IGF-1). We will explore its potential benefits for muscle building and fat loss, as well as the associated risks and side effects. In particular, we will look at the scientific evidence underlying IGF-1 LR3.
Natasha Puttick

Natasha Puttick

Graduate medical student at Barts and London.

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What is IGF-1 LR3?

IGF-1 LR3, also known as Long-Arg3-IGF-I, is a synthetic analog of Insulin-like Growth Factor 1 (IGF-1). It has a similar structure to IGF-1 but with a much lower affinity for IGF-binding proteins compared to native IGFs-I and -II. This means that it binds less readily to these proteins, which can influence its biological activity [1].

However, it's important to note that while IGF-1 LR3 shares similarities with IGF-1, it is not identical and may have different effects in the body. As such, it should be used with caution and under appropriate supervision.

Benefits of IGF-1 LR3 for Muscle Building

IGF-1 LR3 may be able to stimulate muscle growth and prevent muscle wasting. It activates the IGF1R/IRS1/PI3K/Akt pathway, which induces skeletal muscle hypertrophy [2]. A study showed that IGF-1 LR3 increased the phosphorylation of AKT1, a key effector of IGF-1 signalling, promoting muscle differentiation [3].

IGF-1 LR3 also has the potential to enhance muscle repair. It increases the proliferative capacity of MSCs, which are crucial for muscle repair and regeneration [3]. Moreover, IGF-1 LR3 can potentially inhibit muscle proteolysis (breakdown), thus preserving muscle protein content and mass [4].

Risks of IGF-1 LR3 for Muscle Building

Despite its potential benefits, IGF-1 LR3 also carries risks. High concentrations of IGF-1 are associated with an increased risk of cancer and mortality [5]. This is because IGF-1 promotes cell growth and division, which can lead to uncontrolled cell proliferation, a hallmark of cancer.

Another risk is hypoglycemia or low blood sugar. IGF-1 has insulin-like effects, which can lower blood sugar levels, potentially leading to hypoglycemia if not properly managed [4].

Lastly, while IGF-1 LR3 can promote muscle growth, it may not necessarily lead to increased strength. One study found that while muscle mass increased, muscle strength did not improve correspondingly [6].

What evidence is there for IGF-1 LR3 for fat loss?

Insulin-like growth factor-I (IGF-I) is known to have anabolic or protein building effects, which can influence body weight and composition. However, the specific analogue of IGF-I, known as LR(3) IGF-I, does not appear to directly contribute to fat loss. In a study conducted on rats, LR(3)IGF-I was infused at varying levels of food intake. The results showed that while the rats infused with LR(3)IGF-I maintained higher body weight and nitrogen retention, muscle protein was not conserved. Interestingly, LR(3)IGF-I infusion increased fat loss only in young rats, despite a reduction in plasma insulin levels in both age groups [1].

In another study, it was found that metformin treatment in cancer survivors with obesity led to significant decreases in IGF-1 levels, which was associated with weight loss. However, this effect seemed to wane over time [7].

What are the possible side effects of taking IGF-1 LR3?

There may not be sufficient evidence to answer exactly about the risks of IGF-1 LR3 as there are few studies specifically mentioning IGF-1 LR3. However, they do provide information about the general risks associated with alterations in levels of Insulin-like Growth Factor 1 (IGF1) and its binding proteins.

IGF1 has anabolic and growth-promoting effects, which raises concerns about its potential to promote tumor growth [8]. For instance, higher levels of a binding protein called IGFBP3 were associated with an increased incidence of colorectal cancer in older men [8]. Similarly, certain polymorphisms in the IGF1 gene were associated with an increased risk of childhood acute lymphoblastic leukemia [9].

In terms of metabolic diseases, higher levels of IGFBP-3 might raise the risk of type 2 diabetes mellitus (T2DM) independent of IGF-1 levels [10]. Both low and high IGF1 levels were associated with an increased risk of developing diabetes [11].

In terms of cardiovascular health, higher IGFBP1 and lower IGFBP3 levels were found to predict overall and cardiovascular disease-related mortality in older men [11].

It's important to note that these risks are associated with alterations in the levels of IGF1 and its binding proteins, not specifically IGF-1 LR3. More research is needed to understand the specific risks associated with IGF-1 LR3.


While IGF-1 and its analogues can influence body weight and composition, the evidence does not strongly support the use of IGF-1 LR3 specifically for fat loss or muscle building. More research is needed to fully understand the potential benefits and limitations of IGF-1 LR3 in this context.

Crucially if you are thinking of taking these supplements, please consider the risks carefully as discuss with a licensed medical practitioner as they are often under-researched and the side effects ill understood. Additionally, some peptides are illegal to purchase in certain countries.

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Natasha Puttick

Natasha Puttick

Natasha is a medical student at Barts and the London school of Medicine and Dentistry, with an interest in the social determinants of health. She graduated from the University of Oxford with a BA in Human Sciences and has obtained two publications. Her most recent work investigating clinical vaccine trials has been published in BMJ Public Health.