How to Inject Testosterone in the Thigh (Vastus Lateralis)
The outer thigh is the IM site you can see, reach and landmark with no mirror and no helper, and it is also a common SubQ site. What matters is staying on the outer side of the thigh, in its middle third. The front of the thigh and the inner thigh are where the nerves and large vessels are.
- The IM target is the vastus lateralis, the outer quadriceps. Mark one hand-width below the hip bone (greater trochanter) and one hand-width above the knee, and inject into the outer part of the middle third.
- A cadaver and ultrasound study found no major vessels or nerves near the midpoint of the vastus lateralis. At the midpoint of the rectus femoris, the muscle on the front of the thigh, it often found an artery branch and femoral nerve branches.
- Most adults need a 1–1.5 inch needle for IM injections in the thigh. The fat layer measured under 10 mm in most men and 8–13 mm on average in women.
- Nursing references allow up to 3 mL per thigh injection in adults. For SubQ testosterone, the thigh is one of the two sites used in studies, but the Xyosted autoinjector is labeled for the abdomen only.
If you inject testosterone on your own, the thigh is usually the easiest IM site to learn. You can sit down, see the whole site, use both hands, and check your landmarks without twisting around. It is also a large muscle with plenty of room, unlike the deltoid. The mistakes people make here are mostly about direction: drifting to the front of the thigh or toward the inner thigh. This guide covers the landmarks, the anatomy behind them, needle length for your build, volume, and how the SubQ thigh injection differs. It is one of three site guides linked from our injection sites hub. For the full step-by-step procedure, see how to inject testosterone. Note that the testosterone cypionate label specifies the gluteal muscle for IM injections8, so confirm with your prescriber that the thigh is approved for you.
Which muscle you are aiming for
The front of the thigh is the quadriceps, which is four muscles. The one you want is the vastus lateralis, on the outer (lateral) side of the thigh, running from just below the hip to just above the knee. Directly in the middle at the front is the rectus femoris. A study that combined ultrasound in young adults with cadaver dissection mapped what lies under each candidate site. At the midpoint of the rectus femoris, it often found the descending branch of the lateral circumflex femoral artery and muscle branches of the femoral nerve. These structures run downward behind the rectus femoris, along the border between the vastus intermedius and the vastus lateralis. At the midpoint of the vastus lateralis, they were absent. The authors concluded that "the middle of the vastus lateralis is an appropriate site for intramuscular injections because of the low risk of vascular or nerve damage"1.
The inner thigh is the other area to avoid. The large femoral vessels run there, and there is no reason to inject near them when the outer thigh is available.
How to find the thigh injection site, step by step
- Sit down with the thigh relaxed and the foot flat, so the muscle is not bearing weight. Expose the whole thigh from hip to knee.
- Find the greater trochanter, the bony knob on the outside of the upper thigh just below the hip, and place one hand's width below it. That marks the top of the site3,4.
- Find the top of the knee and place one hand's width above it. That marks the bottom3,4.
- The zone between your hands is the middle third. The study above placed its safe point at the middle of the lateral thigh, between the greater trochanter and the lateral epicondyle, the bony bump on the outside of the knee1.
- Move to the outer side. Open RN describes the site as the "outer middle third" of the muscle4. A useful check: if you picture a trouser seam running down the outside of the leg, the target is on or just in front of it, not on the top of the thigh.
- Spread the skin taut and insert the needle at 90 degrees2,3.
Needle length for a thigh injection
The CDC's guidance for the adult thigh is that "most adolescents and adults will require a 1- to 1.5-inch (25–38 mm) needle to ensure intramuscular administration"2. Open RN gives the same 1–1.5 inch range for adults at this site4. The anatomical study measured the tissue directly1:
| Measurement (vastus lateralis) | Men | Women |
|---|---|---|
| Fat layer over the thigh sites | Under 10 mm at all sites (maximum 15 mm) | 8–13 mm on average (maximum 21 mm at the vastus lateralis midpoint) |
| Muscle thickness at the midpoint | 19 ± 5 mm (range 13–29) | 17 ± 6 mm (range 9–23) |
The same study found that a standard 23-gauge, 32 mm needle got through the fat to muscle at every site it examined1. Two practical points follow from this. A lean, muscular thigh usually needs the shorter end of the range. A thigh with more fat, which in this study meant women more often than men, needs a needle long enough to clear it, or the oil ends up in the fat. The CDC notes that if a shorter 5/8 inch needle is used for IM injections in a small adult, the skin must be stretched tight and the tissue must not be bunched up2. Bunching adds depth that the needle then fails to get through.
For gauge, nursing texts list 18–21G for oily or viscous IM solutions4. Testosterone cypionate is dissolved in cottonseed oil8. Finer needles still work for oil, but slowly, so the gauge is a trade-off between flow and comfort that your prescriber sets.
How much volume the thigh takes
Open RN puts the maximum for a single adult injection into the vastus lateralis at 3 mL4, the same as the ventrogluteal site and well above the deltoid's usual 1 mL4. Larger-volume injections into the thigh have also been studied. In a small study of long-acting HIV injections, 3 mL doses into the lateral thigh had safety profiles comparable to the same injections in the gluteal muscle, although every participant reported some injection-site pain9. That was a different drug in a different vehicle, so it says little about testosterone oil specifically, beyond showing that the muscle can take a 3 mL volume. At the label's 200 mg/mL strength8, 1 mL is 200 mg. The TRT dose calculator converts your prescribed dose into millilitres and syringe units.
SubQ testosterone in the thigh
The thigh is also one of the two sites used in subcutaneous testosterone studies; the other is the abdomen, about 3–5 cm to the side of the navel5. A SubQ injection is a different procedure from an IM one. The needle is short, usually a 5/8 inch needle at 20–25 gauge in the published studies, and the review's authors say a 23-gauge needle "can be used without difficulty" with the long-acting esters5. The dose goes into the fat layer rather than through it. The same review found local reactions after SubQ testosterone were "mild and transient," with reported reactions including redness, induration, bruising and haematoma5.
One exception: the Xyosted autoinjector (SubQ testosterone enanthate) is labeled "for subcutaneous injection in the abdominal region only," and its instructions say not to inject it in any other area of the body6. If you use Xyosted, the thigh is not an option. For how the two routes compare in levels, comfort and switching, see SubQ vs IM testosterone.
Pain and soreness in the thigh
Some soreness when you walk or climb stairs for a day or two is normal after an oil injection into a working muscle. Relaxing the leg before the injection and pushing slowly, at about 10 seconds per mL according to nursing texts3, are the simplest ways to reduce it. In a meta-analysis of IM injection technique, firm manual pressure on the site and rhythmic tapping reduced injection pain, while the evidence for the Z-track technique was insufficient7. Warming and shaking the vial redissolves any crystals that form in storage8.
Contact your clinician about a sharp, electric pain during the injection, numbness or tingling in the thigh afterwards, redness or warmth that spreads, or a lump that is still firm after about a week. Do not keep injecting into a spot that has not settled.
Common thigh injection mistakes
- Injecting into the top of the thigh (the rectus femoris) instead of the outer side. This moves the needle toward the artery and nerve branches the anatomical study found there.
- Drifting toward the inner thigh.
- Going too high near the hip or too low near the knee, instead of staying in the middle third.
- Pinching the skin up with an IM needle, which makes the injection shallower. Pinching is for SubQ.
- Injecting while standing with your weight on that leg, which tenses the muscle.
- Using the same thigh, and the same point, every time.
Rotation
Alternate left and right thighs and move the entry point at least an inch up or down within the middle third each time. The outer thigh has a long target zone, which makes rotating within it easy. Many self-injectors combine the thighs with the deltoid, and use the ventrogluteal hip when a partner can help. The injection sites hub compares all three sites and includes a rotation schedule. Peptide Me logs each injection to a point on a body map and suggests the site you have used least recently.
Disclaimer: this guide describes general anatomy and published injection guidance and is not medical advice. Testosterone is a prescription, controlled medication. Your prescriber or nurse should confirm which sites and which route are right for you and show you the thigh site in person before your first self-injection.
FAQ
References
Primary sources — PubMed / NEJM / The Lancet.
- Nakajima Y, Fujii T, Mukai K, et al. Anatomically safe sites for intramuscular injections: a cross-sectional study on young adults and cadavers with a focus on the thigh. Hum Vaccin Immunother. 2020;16(1):189-196. https://pmc.ncbi.nlm.nih.gov/articles/PMC7012163/
- Centers for Disease Control and Prevention. Chapter 6: Vaccine Administration. In: Epidemiology and Prevention of Vaccine-Preventable Diseases (Pink Book). https://www.cdc.gov/pinkbook/hcp/table-of-contents/chapter-6-vaccine-administration.html
- OpenStax. Clinical Nursing Skills (senior contributor Christy Bowen). Section 12.6: Administering Intramuscular Injections. OpenStax; 2024. https://openstax.org/books/clinical-nursing-skills/pages/12-6-administering-intramuscular-injections
- Ernstmeyer K, Christman E, eds. Nursing Skills (Open RN), Chippewa Valley Technical College. Chapter 18.6: Administering Intramuscular Medications. https://med.libretexts.org/Bookshelves/Nursing/Nursing_Skills_(OpenRN)/18:_Administration_of_Parenteral_Medications/18.06:_Administering_Intramuscular_Medications
- Figueiredo MG, Gagliano-Jucá T, Basaria S. Testosterone Therapy With Subcutaneous Injections: A Safe, Practical, and Reasonable Option. J Clin Endocrinol Metab. 2022;107(3):614-626. https://academic.oup.com/jcem/article/107/3/614/6410585
- XYOSTED (testosterone enanthate) injection, prescribing information. Revised July 2025. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=8a3d204c-be26-49e0-8599-0ac12a272e81
- Ayinde O, Hayward RS, Ross JDC. The effect of intramuscular injection technique on injection associated pain; a systematic review and meta-analysis. PLoS One. 2021;16(5):e0250883. https://pmc.ncbi.nlm.nih.gov/articles/PMC8092782/
- DEPO-TESTOSTERONE (testosterone cypionate) injection, prescribing information. Pharmacia & Upjohn Company LLC. Revised June 2025. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=735b5bf3-4464-412c-a072-1bd02f2e5380
- Han K, Gevorkyan H, Sadik Shaik J, et al. Pharmacokinetics and tolerability of cabotegravir and rilpivirine long-acting intramuscular injections to the vastus lateralis (lateral thigh) muscles of healthy adult participants. Antimicrob Agents Chemother. 2024;68(1):e00781-23. https://pmc.ncbi.nlm.nih.gov/articles/PMC10777827/