What are the side effects of IGF-1 growth hormone?

October 12, 2025 •

4 min read

In clinical trials, hypoglycemia (low blood sugar) was the most common adverse reaction to mecasermin, the lab-created form of IGF-1, affecting 47% of patients [1.8.2]. Understanding what are the side effects of IGF-1 growth hormone is critical for anyone considering or undergoing this therapy.

Quick Summary

Insulin-like Growth Factor-1 (IGF-1) carries a range of potential side effects, from common, manageable issues like hypoglycemia to more severe risks such as tonsillar hypertrophy, intracranial hypertension, and a complex association with cancer.

Key Points

Hypoglycemia is Primary: The most common acute side effect of IGF-1 therapy is hypoglycemia (low blood sugar), affecting nearly half of patients in clinical trials and requiring careful management [1.8.2].
Tissue Overgrowth: A key side effect is hypertrophy (enlargement) of tissues, most notably the tonsils and adenoids, which can cause breathing and swallowing issues [1.8.2].
Serious Skeletal Risks: In children, IGF-1 can cause serious bone problems like slipped capital femoral epiphysis (a hip dislocation) and increased pressure inside the skull (intracranial hypertension) [1.3.2, 1.3.4].
Cancer Association: High levels of IGF-1 are associated with an increased risk of developing certain cancers, like prostate and breast cancer, because the hormone promotes cell growth and survival [1.7.1, 1.7.2].
Off-Label Dangers: Misuse of IGF-1 for bodybuilding at high doses dramatically increases risks, leading to irreversible acromegaly-like symptoms, heart enlargement, and metabolic damage [1.2.2, 1.4.2].
Injection Site Reactions: Localized reactions, including lumps of fatty tissue (lipohypertrophy), pain, and redness, are very common at the injection site [1.8.2].
Medical Supervision is Essential: Due to its potent effects and significant risk profile, IGF-1 therapy must be conducted under the strict supervision of a healthcare professional [1.3.3].

Understanding IGF-1 and Its Function

Insulin-like Growth Factor-1 (IGF-1) is a hormone that, along with Growth Hormone (GH), plays a crucial role in normal growth and development [1.4.3]. Primarily produced by the liver in response to GH stimulation, IGF-1 mediates many of the anabolic effects of GH, promoting the growth of bones and other tissues [1.4.1].

The pharmaceutical version of IGF-1 is a recombinant form called mecasermin (brand name Increlex). It is approved for treating severe height deficits in children with Primary IGF-1 Deficiency (Primary IGFD) or GH gene deletion who have developed neutralizing antibodies to GH [1.8.4]. While it has legitimate medical applications, IGF-1 is also misused for its potential muscle-building and anti-aging effects, often in supraphysiological (higher than normal) doses that significantly increase health risks [1.2.2, 1.5.3].

Common Side Effects of Medically Supervised IGF-1 Therapy

When used as prescribed, the most frequently reported side effects are directly related to IGF-1's powerful metabolic and growth-promoting actions [1.8.2].

Hypoglycemia (Low Blood Sugar)

The most common side effect is hypoglycemia, reported in up to 47% of patients in clinical studies [1.8.2]. Because IGF-1 mimics some actions of insulin, it can cause a rapid uptake of glucose from the blood into cells, leading to symptoms like [1.2.2, 1.3.3]:

Dizziness and headache
Anxiety, shakiness, or irritability
Sweating and chills
Increased hunger
Confusion or difficulty concentrating

To mitigate this, patients are advised to consume a meal or snack 20 minutes before or after an injection [1.3.3].

Injection Site Reactions

Local reactions at the injection site are also very common. These can include [1.8.2]:

Lipohypertrophy (lumps or hardening of fat under the skin), affecting around 32% of users.
Pain, redness, bruising, or itching.

Rotating injection sites is recommended to minimize these issues [1.6.1].

Tonsillar and Adenoidal Hypertrophy

Enlargement of the tonsils and adenoids is another notable side effect, occurring in 16-22% of patients [1.8.2]. This can lead to snoring, difficulty breathing or swallowing, sleep apnea, and fluid in the middle ear [1.3.2, 1.8.3]. Regular monitoring by a doctor is often required [1.3.2].

Serious and Long-Term Side Effects

More severe complications can arise, particularly with long-term use or high doses.

Intracranial Hypertension

IGF-1 can cause increased pressure inside the skull (intracranial hypertension) [1.3.4, 1.8.3]. Symptoms that require immediate medical attention include severe headaches, nausea, vomiting, and vision problems like blurred vision [1.3.3, 1.8.3].

Musculoskeletal Issues

Rapid growth spurred by IGF-1 can lead to musculoskeletal complications. Slipped capital femoral epiphysis, a condition where the head of the thighbone dislocates at the hip, has been reported [1.3.2, 1.8.1]. Patients who develop a limp or pain in the hip or knee should be evaluated by a doctor immediately [1.8.1]. Worsening of pre-existing scoliosis (curvature of the spine) can also occur due to rapid growth [1.8.5].

Cancer Risk

One of the most serious concerns is the relationship between IGF-1 and cancer. Because IGF-1 is a potent factor that promotes cell growth and inhibits apoptosis (programmed cell death), there is a theoretical risk that it could accelerate the growth of existing tumors [1.2.2, 1.7.5]. Epidemiological studies have shown associations between higher circulating IGF-1 levels and an increased risk for certain cancers, including breast, prostate, and colorectal cancer [1.7.1, 1.7.2]. While there is no direct evidence that IGF-1 causes cancer, its use is contraindicated in patients with active or suspected tumors [1.8.4].

Side Effects from Off-Label and High-Dose Use

Using IGF-1 without medical supervision, as is common in bodybuilding and anti-aging circles, involves doses that can be much higher than therapeutic levels. This dramatically elevates the risk profile [1.2.2, 1.5.3].

Acromegaly-like Symptoms: Prolonged use of high doses can lead to irreversible changes similar to the condition acromegaly, including the thickening of bones in the jaw, forehead, hands, and feet [1.2.2, 1.4.2].
Cardiovascular Issues: High doses can contribute to heart enlargement (cardiomegaly), heart murmurs, and an increased risk of heart disease [1.3.4, 1.4.2, 1.4.3].
Metabolic Disruption: While therapeutic doses can improve insulin sensitivity, chronic exposure to high levels of IGF-1 can lead to insulin resistance, the opposite effect [1.2.2].

Comparison: Therapeutic Use vs. Off-Label Abuse


Feature	Therapeutic Use (Mecasermin)	Off-Label Use (e.g., Bodybuilding)
Primary Goal	Treat severe growth failure in children with Primary IGFD [1.8.4].	Enhance muscle mass, fat loss, and athletic performance [1.2.2, 1.5.4].
Dosage	Medically determined and monitored based on weight [1.8.4].	Often supraphysiological (very high) and anecdotal [1.2.2].
Supervision	Under strict guidance of an endocrinologist [1.3.3].	Typically self-administered without medical oversight [1.5.3].
Most Common Risks	Hypoglycemia, injection site reactions, tonsillar hypertrophy [1.8.2].	Severe hypoglycemia, insulin resistance, water retention [1.2.2].
Serious Risks	Intracranial hypertension, slipped capital femoral epiphysis [1.3.2].	Acromegaly-like symptoms, heart enlargement, accelerated cancer risk [1.2.2, 1.4.2].

Conclusion

While IGF-1 is a vital hormone with specific and important medical uses under the brand name Increlex (mecasermin), it is also associated with a significant list of side effects [1.8.2]. The most common are hypoglycemia and injection site reactions, which can be managed with proper medical care [1.3.3]. However, the potential for serious long-term consequences like bone problems, intracranial hypertension, and a debated but plausible link to increased cancer risk necessitates careful consideration and strict medical supervision [1.3.2, 1.7.2]. The risks are magnified exponentially with off-label use for performance enhancement, where high, unregulated doses can lead to permanent and life-threatening conditions [1.5.3].

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Consult with a qualified healthcare professional before making any decisions related to your health or treatment.

An authoritative outbound link on IGF-1 from the U.S. Anti-Doping Agency (USADA)

Frequently Asked Questions

The most common side effect of medically-approved IGF-1 (mecasermin) is hypoglycemia, or low blood sugar, which was reported in 47% of patients during clinical trials [1.8.2].

While there is no definitive proof that IGF-1 directly causes cancer, it is a powerful promoter of cell growth and can inhibit natural cell death [1.7.5]. Studies show that higher circulating levels of IGF-1 are associated with an increased risk of developing certain cancers, such as prostate, breast, and colorectal cancer [1.7.1, 1.7.2].

Yes, long-term use of high doses of IGF-1, particularly in off-label abuse for bodybuilding, can cause acromegaly-like symptoms, which include irreversible bone thickening in the jaw, forehead, hands, and feet [1.2.2, 1.4.2].

No, it is not considered safe. Using IGF-1 for bodybuilding involves supraphysiological doses without medical supervision, which significantly increases the risk of serious health problems like heart enlargement, insulin resistance, irreversible bone changes (acromegaly), and potentially accelerating cancer growth [1.2.2, 1.4.2, 1.5.3].

In a clinical setting, hypoglycemia is managed by ensuring the patient eats a meal or snack containing carbohydrates and protein within 20 minutes of the injection [1.3.3]. Patients are also taught to recognize symptoms and carry a quick source of sugar [1.3.3].

Signs of a serious reaction require immediate medical attention and include: symptoms of intracranial hypertension (severe headache, nausea, vision changes), hip or knee pain with a limp, and signs of a severe allergic reaction (hives, difficulty breathing, swelling of the face or throat) [1.8.3, 1.3.2].

Tonsillar hypertrophy is the enlargement of the tonsils, which is a common side effect of IGF-1 therapy [1.8.2]. It can cause snoring, difficulty breathing (especially during sleep), and ear infections [1.8.3].