From the Guidelines
Intramuscular testosterone injections are recommended over subcutaneous injections for testosterone replacement therapy (TRT) due to their lower costs and similar clinical effectiveness and harms. When considering the administration of testosterone for age-related low testosterone, the method of delivery is crucial for patient outcomes. Subcutaneous and intramuscular testosterone injections have different administration techniques, absorption rates, and side effect profiles. Subcutaneous injections are given into the fatty tissue beneath the skin, providing more stable testosterone levels with fewer peaks and troughs, whereas intramuscular injections deliver testosterone deeper into muscle tissue, creating higher peak levels followed by more significant drops 1.
The American College of Physicians suggests that clinicians consider intramuscular rather than transdermal formulations when initiating testosterone treatment to improve sexual function in men with age-related low testosterone, as costs are considerably lower for the intramuscular formulation and clinical effectiveness and harms are similar 1. The typical intramuscular dose ranges from 100-200mg every 1-2 weeks of testosterone cypionate or enanthate. While subcutaneous injections may cause less scarring and less post-injection pain, the decision between methods should prioritize the patient's preferences, comfort with self-injection, and individual response to therapy, with dose adjustments based on regular blood work monitoring testosterone levels.
Key differences between subcutaneous and intramuscular injections include:
- Administration technique: Subcutaneous injections use shorter needles and are administered into fatty tissue, while intramuscular injections use longer needles and deliver testosterone into muscle tissue.
- Absorption rate: Subcutaneous injections provide more stable testosterone levels, while intramuscular injections create higher peak levels followed by more significant drops.
- Side effect profile: Subcutaneous injections may cause small nodules at injection sites, while intramuscular injections can cause mood and energy fluctuations due to the peaks and troughs in testosterone levels.
- Cost: Intramuscular injections are considerably lower in cost compared to transdermal formulations, making them a more economical option for patients 1.
From the Research
Comparison of Subcutaneous and Intramuscular Testosterone Injections
- Subcutaneous testosterone injections have been shown to have a lower testosterone peak-to-trough ratio compared to intramuscular injections, which can mitigate significant rises in estradiol, hematocrit, and prostate specific antigen 2.
- A study comparing intramuscular testosterone cypionate and subcutaneous testosterone enanthate found that both treatments provided a significant increase in total testosterone levels, but subcutaneous injections were associated with lower levels of post-therapy estradiol and hematocrit 2.
- Subcutaneous administration of testosterone esters has gained popularity due to its ease of self-administration and reduced discomfort compared to intramuscular injections 3.
- Available evidence suggests that subcutaneous testosterone therapy results in comparable pharmacokinetics and mean serum testosterone levels to intramuscular therapy, with the added benefit of easier self-administration 3.
Safety and Efficacy of Subcutaneous Testosterone Injections
- Subcutaneous testosterone injections have been found to be an effective testosterone delivery system with a potentially preferable safety profile compared to intramuscular injections 2.
- Clinicians should consider discussing the subcutaneous route with patients due to its ease of self-administration and potential to improve patient adherence 3.
- However, further studies are needed to determine the long-term safety and efficacy of subcutaneous testosterone injections, particularly with regards to cardiovascular health 4, 5.
Guidelines for Testosterone Replacement Therapy
- The Society for Endocrinology has published guidelines for testosterone replacement therapy in male hypogonadism, which provide a multidisciplinary approach to treating patients with hypogonadism 6.
- These guidelines emphasize the importance of individualized treatment and monitoring for adverse effects, and highlight the need for further research on the long-term safety and efficacy of testosterone replacement therapy 6.
- Other guidelines and reviews have also emphasized the importance of careful patient evaluation and monitoring, as well as the need for further studies on the impact of testosterone replacement therapy on cardiovascular health 4, 5.