What is the effect of Insulin-like Growth Factor 1 (IGF-1) Long Arg3 (LR3) on muscle growth?

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Last updated: April 19, 2025View editorial policy

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From the Guidelines

IGF-1 LR3 is not recommended for muscle growth due to safety concerns and limited evidence supporting its effectiveness. The use of IGF-1 LR3, a synthetic analog of insulin-like growth factor 1, is not approved by regulatory agencies for human use and is primarily sold as a research chemical 1. While some bodybuilders and athletes use it to promote muscle growth, the typical underground dosages range from 20-100mcg daily, usually injected subcutaneously, with cycles lasting 4-8 weeks. However, using IGF-1 LR3 carries significant risks including potential cancer promotion, hypoglycemia, acromegaly (abnormal growth of extremities), and organ enlargement.

The compound works by binding to IGF-1 receptors, stimulating muscle cell proliferation and protein synthesis, while inhibiting protein breakdown. Despite theoretical benefits, clinical evidence supporting its muscle-building effects in humans is lacking, and safer, legal alternatives exist for muscle growth including proper nutrition, resistance training, adequate sleep, and approved supplements like creatine and protein. In fact, the 2014 female athlete triad coalition consensus statement highlights the importance of nutritional intervention in normalizing gonadotropin pulsatility and secretion, rather than relying on exogenous hormones or growth factors 1.

Key points to consider when evaluating the use of IGF-1 LR3 for muscle growth include:

  • Lack of regulatory approval for human use
  • Limited clinical evidence supporting its effectiveness
  • Significant safety concerns, including potential cancer promotion and organ enlargement
  • Availability of safer, legal alternatives for muscle growth
  • Importance of nutritional intervention in normalizing gonadotropin pulsatility and secretion, as highlighted in the 2014 female athlete triad coalition consensus statement 1.

Overall, the risks associated with IGF-1 LR3 use outweigh any potential benefits, and individuals seeking to promote muscle growth should prioritize evidence-based, safe, and legal methods.

From the Research

IGF-1 LR3 and Muscle Growth

  • IGF-1 LR3 is a synthetic analogue of insulin-like growth factor 1 (IGF-1), which plays a crucial role in muscle growth and development 2.
  • Research suggests that IGF-1 is involved in the regulation of muscle hypertrophy, and its levels can be influenced by various factors, including resistance training and nutrition 3, 4.
  • Studies have shown that resistance training can increase muscle IGF-1 content, and this increase is associated with muscle hypertrophy 5.
  • Additionally, certain supplements such as creatine have been shown to increase muscle IGF-1 content and enhance muscle hypertrophy when combined with resistance training 5.
  • However, the use of anabolic steroids and other performance-enhancing drugs can also increase muscle IGF-1 levels and lead to supraphysiological muscle hypertrophy, but this is associated with significant side effects and health risks 4, 2.

Mechanisms of Muscle Hypertrophy

  • Muscle hypertrophy is a complex process that involves multiple factors, including mechanical tension, muscle damage, and metabolic stress 3.
  • Resistance training is a key stimulus for muscle hypertrophy, and the type and intensity of training can influence the magnitude of muscle growth 3, 6.
  • Nutrition also plays a critical role in muscle hypertrophy, and adequate protein intake is essential for muscle growth and repair 4, 6.
  • The timing and type of protein supplementation can also influence muscle hypertrophy, with some studies suggesting that post-exercise protein supplementation can enhance muscle growth and repair 6.

Limitations and Future Directions

  • While there is evidence to suggest that IGF-1 LR3 can enhance muscle growth, more research is needed to fully understand its effects and potential side effects 2.
  • Further studies are also needed to determine the optimal training and nutrition protocols for maximizing muscle hypertrophy, and to explore the potential benefits and risks of using performance-enhancing drugs and supplements 3, 4, 6, 5, 2.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

The role of hormones in muscle hypertrophy.

The Physician and sportsmedicine, 2018

Research

The mechanisms of muscle hypertrophy and their application to resistance training.

Journal of strength and conditioning research, 2010

Research

Making muscles "stronger": exercise, nutrition, drugs.

Journal of musculoskeletal & neuronal interactions, 2004

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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