Intramuscular Testosterone Injection Sites
For intramuscular testosterone injections, inject deep into the gluteal muscle or the anterolateral thigh (vastus lateralis), with the gluteal site being the FDA-approved standard location and the thigh offering a safe, accessible alternative for self-administration. 1, 2
FDA-Approved Primary Site
The FDA label for testosterone cypionate explicitly states that intramuscular injections should be given deep in the gluteal muscle. 2 This remains the gold standard site recommended in the official prescribing information.
Alternative Self-Administration Site
The anterolateral thigh (vastus lateralis) is an excellent alternative, particularly for patients who self-inject. 1 The American College of Gastroenterology specifically recommends that testosterone enanthate or cypionate can be self-administered in the thighs or given by another person in the gluteal region. 1
Sites to Avoid
Do not inject testosterone into the deltoid muscle. 3 A 2022 case report documented recurrent localized rhabdomyolysis when a patient switched from thigh/gluteal injections to deltoid injections, theorizing that the relative increase in testosterone dose and volume per gram of smaller deltoid muscle precipitated this serious complication. 3 While older studies from 1995 included deltoid injections in their tolerability assessments, current evidence suggests avoiding this site due to safety concerns. 4
The abdomen and upper arm are not appropriate sites for intramuscular testosterone—these locations are reserved for subcutaneous medications like insulin. 1
Anatomical Safety Considerations
The middle of the vastus lateralis (anterolateral thigh) has been demonstrated to be anatomically safe with low risk of vascular or nerve damage. 5 In contrast, the middle of the rectus femoris contains the descending branch of the lateral circumflex femoral artery and muscle branches of the femoral nerve, making it a less desirable injection site. 5
Practical Administration Details
- Use an 18-gauge needle for drawing testosterone from the vial 1
- Use a 21-23 gauge, 1-1.5 inch needle for the actual intramuscular injection 1
- Longer needles (1.5 inch) are typically needed for gluteal injections 1
- Shorter needles (1 inch) may suffice for thigh injections in leaner patients 1
- Inject deep into the muscle to ensure proper intramuscular deposition 2
Subcutaneous Alternative
Subcutaneous injection is an increasingly preferred alternative to intramuscular administration, offering comparable efficacy with less discomfort and easier self-administration. 1, 6 A 2017 study of 63 transgender patients demonstrated that subcutaneous testosterone achieved therapeutic levels across a wide BMI range (19.0-49.9 kg/m²) with doses of 50-150 mg weekly, and 20 out of 22 patients who switched from intramuscular to subcutaneous had a marked preference for the subcutaneous route. 6
Common Pitfall
The most critical error is using the deltoid muscle for testosterone injections, which carries documented risk of localized rhabdomyolysis. 3 Patients who have been safely injecting into larger muscles (thigh or gluteus) for years can develop serious complications when switching to the smaller deltoid muscle due to the concentrated dose per gram of muscle tissue. 3