Zomacton Side Effects: What to Expect and When to Call Your Doctor

Zomacton (somatropin) is a recombinant human growth hormone that is generally well tolerated by pediatric and adult patients alike. However, like any prescription medication, it can cause side effects — some minor and manageable, others serious enough to require contacting your doctor immediately. Understanding what to expect helps you stay safe during treatment.

This guide covers the most important side effects associated with Zomacton, based on the FDA-approved prescribing information and clinical data. Always discuss your specific medical history with your prescribing endocrinologist before starting treatment.

Common Side Effects of Zomacton

The most frequently reported side effects in adult and pediatric patients receiving Zomacton — those occurring in 10% or more of patients in clinical trials — include:

• Upper respiratory infection — colds and respiratory illnesses occur more commonly in pediatric patients on growth hormone therapy
• Fever — more common in children; usually mild and transient
• Pharyngitis (sore throat)
• Headache — mild headaches are common, particularly early in therapy
• Otitis media (ear infections) — more frequent in Turner syndrome patients in particular
• Edema (fluid retention / swelling) — usually mild and dose-dependent; more common in adult patients
• Arthralgia (joint pain) and myalgia (muscle pain) — typically transient and dose-dependent
• Paresthesia (tingling or numbness) — related to fluid retention affecting nerves; often resolves with dose adjustment
• Carpal tunnel syndrome — more common in adults; usually resolves after dose reduction
• Rhinitis (runny nose) and flu syndrome
• Hypothyroidism — somatropin can unmask or worsen underlying thyroid deficiency; requires periodic monitoring
• Hyperglycemia / impaired glucose tolerance — growth hormone decreases insulin sensitivity; blood sugar should be monitored especially in at-risk patients

Injection Site Reactions

Local injection site reactions are common with any subcutaneous medication. With Zomacton, these may include:

• Redness or bruising at the injection site
• Lipoatrophy (loss of fatty tissue at injection site) from repeated injections in the same spot — prevented by rotating injection sites

Rotating injection sites (upper arm, abdomen, buttock, thigh) is essential to minimize these effects.

Serious Side Effects — Call Your Doctor Promptly

The following side effects are less common but require prompt medical attention:

• Intracranial hypertension (increased brain pressure): Signs include severe headache, visual changes, nausea, and vomiting — most often occurs within the first 8 weeks of treatment. Zomacton must be stopped if papilledema is confirmed.
• Slipped capital femoral epiphysis (SCFE): Affects pediatric patients during rapid growth phases. Signs: limping, hip pain, or knee pain. Contact your pediatrician or endocrinologist immediately if your child develops these symptoms.
• New-onset type 2 diabetes mellitus: Zomacton decreases insulin sensitivity, particularly at higher doses. Symptoms: increased thirst, frequent urination, unexplained fatigue.
• Anaphylaxis / severe allergic reactions: Though rare, serious systemic hypersensitivity reactions including anaphylaxis and angioedema have been reported with somatropin products. Seek emergency care immediately for symptoms like throat tightening, difficulty breathing, or widespread hives.
• Pancreatitis: Abdominal pain, especially in pediatric patients, may indicate pancreatitis. Report to your doctor promptly.
• Progression of scoliosis: Rapid growth can worsen existing spinal curvature. Pediatric patients should be monitored regularly.
• Increased risk of second neoplasms: Childhood cancer survivors treated with brain or head radiation are at increased risk of secondary tumors during growth hormone therapy. Regular monitoring is required.

Special Considerations: Benzyl Alcohol and Infants

The 5 mg Zomacton vial comes with a diluent containing 0.9% benzyl alcohol, which can cause serious and fatal reactions in neonates and infants. If administering Zomacton 5 mg to an infant, reconstitute with normal saline (0.9% sodium chloride injection) instead of the co-packaged diluent. The 10 mg formulation uses a benzyl alcohol-free diluent (0.33% metacresol) and is the preferred formulation for use in lactating mothers.

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When to Seek Emergency Care

Go to the emergency room or call 911 if you or your child experiences:

• Signs of a severe allergic reaction (anaphylaxis): throat tightening, difficulty breathing, widespread swelling, dizziness
• Sudden severe headache with vision changes and vomiting (intracranial hypertension)
• Sudden severe abdominal pain (pancreatitis)

For information on drug interactions with Zomacton, see our guide: Zomacton Drug Interactions: What to Avoid and What to Tell Your Doctor.

For a general overview of Zomacton, see: What Is Zomacton? Uses, Dosage, and What You Need to Know in 2026.