Short answer: The Depo-Testosterone and testosterone enanthate labels do not name a needle gauge or length; they only say the shot goes deep into the gluteal muscle. The closest public reference is CDC's adult intramuscular guidance for vaccines: 22 to 25 gauge, and 1 to 1.5 inches long depending on the site and body weight. Studies show the fat over the hip muscle can be thicker than a 1.5-inch needle reaches in many people with a high BMI, so your prescriber or pharmacist picks the size.
The Depo-Testosterone label says the shot is for intramuscular use only and should be given deep in the gluteal muscle. The testosterone enanthate label says to inject slowly and deeply into the gluteal muscle. Neither label gives a needle gauge or length, so any size you see quoted online comes from clinic habit or general injection guides, not from the drug label.
Both are oil solutions: cypionate is dissolved in cottonseed oil and enanthate in sesame oil, according to their labels. That is one reason the enanthate label asks for a slow injection.
Gauge is the width of the needle. The number runs backwards: a higher gauge is a thinner needle, so 25G is thinner than 22G. Length is given in inches, and it decides how deep the tip ends up.
For an intramuscular shot the needle has to pass through the skin and the fat layer and end in the muscle. MedlinePlus says the needle "needs to be long enough to get deep into the muscle". Too short, and the medicine can end up in the fat layer instead.
CDC's vaccine administration guidance is written for vaccines, not testosterone, but it is the most widely used public reference for adult intramuscular needle sizes:
| Item | CDC guidance |
|---|---|
| Gauge | 22 to 25 gauge |
| Angle | 90 degrees to the skin |
| Upper arm, under 130 lb (60 kg) | 5/8 inch can be enough (the CDC table lists 1 inch) |
| Upper arm, 130 to 152 lb (60 to 70 kg) | 1 inch |
| Upper arm, heavier adults | 1 to 1.5 inches; 1.5 inches for women over 200 lb and men over 260 lb |
| Thigh | 1.5 inches (1 inch if the skin is stretched tight) |
The CDC page does not give adult needle lengths for the hip or buttock, which are the sites the testosterone labels name.
A 2019 study measured the fat over the hip (ventrogluteal) injection site on 350 pelvic MRI scans. Fat thickness rose closely with BMI, and women had more fat than men at the same BMI. The authors estimated that a 1.5-inch (3.75 cm) needle would miss the muscle in 71% of women with a BMI over 30 and 60% of men with a BMI over 35.
A 2023 meta-analysis of ultrasound studies found the fat layer at the hip site averaged about 20 mm (roughly 0.8 inch) and the muscle about 36 to 38 mm, with thicker fat in women. These are averages; your own depth can be quite different.
If you have been told to inject under the skin instead, the needle choice changes completely. A 2017 study gave testosterone cypionate or enanthate under the skin, and Xyosted is an autoinjector labeled for under-the-skin use in the belly. Whether that route suits you is your prescriber's call.
Read more on Dose Track: Needle gauge (glossary) · Intramuscular injection · Syringe dead space · Testosterone enanthate guide · Cypionate vs enanthate · U-40 vs U-100 syringes