Is Growth Hormone Given Subcutaneously or Intramuscularly? A Pharmacological Review

October 12, 2025 •

4 min read

Growth hormone deficiency (GHD) affects approximately 1 in 4,000 to 1 in 10,000 children [1.7.2, 1.7.3, 1.7.5]. The primary treatment involves injections, but is growth hormone given subcutaneously or intramuscularly? The subcutaneous route is now the standard method for chronic therapy [1.2.3, 1.2.4].

Quick Summary

Human Growth Hormone (HGH) is most commonly administered via subcutaneous injection for chronic therapy due to less pain and ease of self-administration. Intramuscular injections offer faster absorption but are more painful and less preferred.

Key Points

Primary Method: Growth hormone is almost always given subcutaneously (into the fat layer under the skin) for chronic therapy [1.2.4].
Absorption Rate: Subcutaneous injections have a slower, more sustained absorption, while intramuscular injections are absorbed much faster [1.2.2, 1.5.3].
Patient Comfort: Subcutaneous injections are significantly less painful and easier to self-administer compared to intramuscular ones [1.2.3, 1.2.5].
Historical Context: Intramuscular injection was a classic method but has been replaced by the subcutaneous route due to patient preference and ease of use [1.2.1, 1.2.2].
Site Rotation: It is crucial to rotate subcutaneous injection sites (abdomen, thighs, arms) to prevent tissue damage like lipoatrophy [1.4.2, 1.4.3].
New Formulations: Long-acting, once-weekly growth hormone preparations are available and are also administered subcutaneously [1.8.4].
Efficacy: Studies show similar growth rates and efficacy between subcutaneous and intramuscular routes, making the less painful SC route the clear choice [1.2.4, 1.2.5].

Understanding Growth Hormone Therapy

Human Growth Hormone (HGH) is a crucial peptide hormone produced by the pituitary gland that stimulates growth, cell reproduction, and regeneration in humans [1.6.2]. It plays a vital role not just in childhood growth but also in maintaining tissue and organ function throughout life, regulating metabolism, and supporting bone health [1.6.3]. When the body doesn't produce enough GH, a condition known as growth hormone deficiency (GHD), synthetic HGH therapy may be prescribed [1.6.3]. This therapy is also approved for other conditions like Turner syndrome, Prader-Willi syndrome, and HIV-associated wasting syndrome [1.6.3]. Historically, growth hormone was administered via intramuscular injection, but modern practice has largely shifted [1.2.1, 1.2.2]. The central question for patients and caregivers is: is growth hormone given subcutaneously or intramuscularly?

The Preferred Method: Subcutaneous (SC) Injection

For chronic HGH therapy, subcutaneous injection is the method of choice [1.2.4]. This technique involves injecting the hormone into the fatty tissue just beneath the skin [1.3.5]. The preference for the SC route is based on several factors:

Less Pain: Patients and parents consistently report less pain and apprehension with subcutaneous injections compared to intramuscular ones [1.2.5].
Ease of Administration: The shallow injection depth and simpler technique make it easier for patients or their family members to perform the injections at home [1.2.5, 1.3.5].
Steady Absorption: The subcutaneous tissue has a less dense blood supply than muscle, leading to a slower, more prolonged absorption and disappearance phase [1.2.2, 1.5.3]. This extended release can be advantageous for maintaining stable GH levels, mimicking the body's natural, pulsatile release, especially overnight [1.2.2, 1.4.3].
Low Incidence of Complications: Studies show that with modern, purer HGH preparations, the risk of developing growth-attenuating antibodies is low with SC injections, a concern with older formulations [1.2.1, 1.2.4].

The Alternative: Intramuscular (IM) Injection

Intramuscular injections deliver the hormone directly into a muscle, such as the deltoid (shoulder), vastus lateralis (thigh), or gluteus maximus (buttocks) [1.2.3]. Because muscle tissue is more vascular than subcutaneous fat, absorption is significantly faster [1.5.2, 1.5.4]. While this rapid uptake might seem beneficial, IM injections for HGH have several drawbacks for routine use:

Increased Pain: IM injections are generally more painful than SC injections [1.2.3].
Higher Skill Requirement: This method requires more skill to perform correctly and carries a greater risk of hitting a nerve or blood vessel [1.2.3, 1.4.5].
Less Convenient: For daily injections, the discomfort and complexity of IM administration make it a less practical long-term solution [1.2.5].

While historically common, the IM route is now less favored for routine HGH therapy but may be chosen in specific clinical situations where rapid absorption is desired [1.2.1, 1.2.3].

Comparison of Injection Methods


Feature	Subcutaneous (SC) Injection	Intramuscular (IM) Injection
Primary Route for HGH	Yes, the standard method for chronic therapy [1.2.4]	No, historically used but now less common [1.2.1]
Absorption Speed	Slower, more sustained release [1.2.2, 1.5.3]	Faster, due to higher blood flow in muscle [1.2.3, 1.5.2]
Pain Level	Lower, generally less painful [1.2.3, 1.2.5]	Higher, more discomfort reported [1.2.3, 1.2.5]
Ease of Self-Administration	High, easy to perform at home [1.3.4, 1.3.5]	Lower, requires more skill and can be difficult [1.2.3]
Injection Sites	Abdomen, thighs, upper arms, buttocks [1.4.1]	Deltoid (shoulder), thigh, buttocks [1.4.1]
Needle Angle	45 to 90 degrees [1.2.3, 1.3.1]	90 degrees [1.2.3]
Risk of Tissue Damage	Risk of lipoatrophy/lipohypertrophy if sites aren't rotated [1.4.3]	Higher risk of nerve or blood vessel injury [1.4.5]

Proper Administration and Site Rotation

Correct injection technique is crucial for maximizing efficacy and minimizing side effects. For subcutaneous injections, common sites include the abdomen (avoiding the navel), the top or outer thighs, the back of the arms, and the buttocks [1.3.5, 1.4.1].

It is essential to rotate injection sites regularly [1.4.2]. Using the same spot repeatedly can lead to lipoatrophy (loss of fat tissue) or lipohypertrophy (a build-up of fat or scar tissue), which can be unsightly and impair the absorption of the hormone [1.4.3]. A systematic rotation plan, such as using a different quadrant of the abdomen each week, helps keep the tissue healthy and ensures consistent absorption [1.4.4].

The Rise of Long-Acting Formulations

To reduce the burden of daily injections, pharmaceutical research has led to the development of long-acting growth hormone (LAGH) preparations. These formulations use various technologies—such as PEGylation, pro-drug technology, or fusion proteins—to extend the hormone's half-life, allowing for once-weekly injections [1.8.1, 1.8.2]. Products like Skytrofa (lonapegsomatropin), Ngenla (somatrogon), and Sogroya (somapacitan) have been approved in various regions for treating GHD [1.8.4]. These weekly options, also administered subcutaneously, have shown comparable efficacy to daily injections and may improve treatment adherence and quality of life [1.8.4].

Conclusion

While growth hormone can be administered both subcutaneously and intramuscularly, the subcutaneous route is the overwhelmingly preferred and standard method for modern HGH therapy. Its lower pain profile, ease of self-administration, and steady absorption kinetics make it a superior choice for the chronic, often daily, regimen required for treating growth hormone deficiency [1.2.4, 1.2.5]. Intramuscular injections, though providing faster absorption, are more painful and complex, relegating them to a minor role in current practice. With the advent of once-weekly subcutaneous formulations, the future of HGH therapy continues to move towards greater patient convenience and adherence.

For more information, you can visit the Endocrine Society's patient resources [1.7.5].

Frequently Asked Questions

Subcutaneous injection is better for routine, long-term HGH therapy because it is less painful, easier to self-administer, and provides a slow, steady release that mimics the body's natural secretion [1.2.3, 1.2.4]. Intramuscular is faster-acting but more painful [1.2.3].

Subcutaneous growth hormone injections use a very small needle and are injected into fatty tissue, so they generally do not hurt much [1.3.5]. Intramuscular injections can be more painful [1.2.3].

It is generally recommended to give HGH injections in the evening before bed. This timing helps to match the body's natural rhythm, as more growth hormone is typically produced at night during sleep [1.4.3].

For subcutaneous injections, common and effective sites include the abdomen (stomach area), the top or outside of the thighs, the back of the upper arms, and the outer buttocks. It's vital to rotate these sites regularly [1.3.5, 1.4.1].

For most daily growth hormone regimens, a missed injection can be given on the seventh day if you are on a six-day-a-week schedule. However, you should consult your healthcare provider for specific instructions regarding missed doses [1.4.3].

Most growth hormone preparations need to be refrigerated. When traveling, you should use a small cooler with an ice or cold gel pack to maintain the correct temperature. Always check the specific storage instructions for your brand of HGH [1.4.3].

Yes, several long-acting growth hormone (LAGH) formulations are now available that only require a once-weekly subcutaneous injection. These have been shown to be effective and can reduce the burden of daily shots [1.8.4].