Can 1 milliliter (mL) of testosterone (cypionate or enanthate) be safely injected into the deltoid muscle?

Can You Inject 1 mL of Testosterone in the Deltoid?

While technically feasible, injecting 1 mL of testosterone cypionate or enanthate into the deltoid muscle is NOT recommended as a primary injection site due to increased risk of localized rhabdomyolysis and should be avoided in favor of the thigh or gluteal muscles. 1, 2

Recommended Injection Sites for Testosterone

The preferred intramuscular injection sites for testosterone cypionate or enanthate are:

• Anterolateral thigh (vastus lateralis) - can be self-administered 1
• Gluteal muscle - typically requires administration by another person 1

These sites are explicitly recommended by current guidelines for testosterone replacement therapy and have been used safely for many years without the complications seen with deltoid injections 1, 2.

Why the Deltoid Should Be Avoided

A case report documented recurrent localized rhabdomyolysis specifically associated with deltoid injections of testosterone enanthate. 2 The patient had successfully used thigh and gluteal sites for years without issues, but developed rhabdomyolysis repeatedly when switching to deltoid injections 2. The proposed mechanism is that the relatively smaller deltoid muscle mass receives a higher concentration of testosterone per gram of muscle tissue, precipitating muscle breakdown 2.

While an older study from 1995 reported that deltoid injections were tolerated in a research setting, this was before the recognition of rhabdomyolysis risk, and notably that study found the gluteal site had fewer overall complaints 3.

Volume and Needle Specifications

For intramuscular testosterone injections:

• Needle gauge: 21-23 gauge for injection (18-gauge for drawing from vial) 1
• Needle length: 1-1.5 inches depending on site 1
  • Longer needles (1.5 inch) for gluteal injections 1
  • Shorter needles (1 inch) may suffice for thigh injections in leaner patients 1
• Syringe size: 1-3 mL syringes (3 mL most common for typical 100-200 mg doses) 1

The 1 mL volume itself is not problematic—the issue is the injection site selection 1.

Safer Alternative: Subcutaneous Administration

If patients prefer self-administration or want to avoid larger muscle injections, subcutaneous testosterone is an effective alternative with comparable efficacy and potentially fewer adverse effects. 1, 2 Subcutaneous dosing of 50-150 mg weekly achieves therapeutic testosterone levels equivalent to intramuscular administration 1. The patient in the rhabdomyolysis case report successfully transitioned to subcutaneous testosterone without recurrence 2.

Common Pitfalls to Avoid

• Do not use the deltoid as a routine injection site for testosterone despite it being acceptable for vaccines and other medications 1, 2
• Do not assume all intramuscular sites are equivalent for testosterone administration—site selection matters for safety 2
• Ensure adequate needle length to reach muscle tissue and avoid subcutaneous deposition, which could alter absorption kinetics 1