Intramuscular (IM) injections can be given in four main sites on the body: the deltoid muscle of the upper arm, the vastus lateralis muscle of the outer thigh, the ventrogluteal muscle of the hip, and the dorsogluteal muscle of the buttock. Each site has different advantages depending on your age, body size, the volume of medication, and whether you’re injecting yourself or someone else is administering it.
The Deltoid (Upper Arm)
The deltoid is the most familiar injection site for most people. It’s where you get flu shots, COVID vaccines, and many other routine immunizations. The target zone sits on the outer side of your upper arm, about four fingerbreadths (roughly 9 cm) below the bony point at the top of your shoulder called the acromion. A 2024 cadaver study published in Cureus identified this spot as the safest location to avoid nerves and blood vessels running through the area.
The deltoid is convenient and easy to access, but it’s a relatively small muscle. That limits how much fluid it can comfortably absorb. Adults can receive 0.5 to 2 mL in the deltoid, which is fine for most vaccines but not enough for larger-volume medications. For children, the deltoid becomes an option once there’s enough muscle mass, typically around age 1 to 2 for toddlers with adequate development.
The Vastus Lateralis (Outer Thigh)
The vastus lateralis runs along the outer part of your thigh. The injection zone is the middle third of the thigh, roughly halfway between your hip bone and your knee. This area sits well away from major blood vessels and nerves, making it one of the safest sites on the body.
This is the go-to site for infants and young children who aren’t yet walking, because their thigh muscles are more developed than their arm muscles at that age. Newborns receive their first injections here, typically with a short 5/8-inch needle. For older infants, a 1-inch needle is standard. But the vastus lateralis isn’t just for babies. Adults can use it too, and it accepts a much larger volume than the deltoid, up to 5 mL per injection.
The thigh is also the most practical site if you need to give yourself an IM injection. You can see the area clearly, reach it easily with both hands, and position the needle at the correct 90-degree angle without contorting your body. If you’ve been prescribed a self-administered IM medication, this is likely the site you’ll be taught to use. Aim for the middle of the outer thigh, staying on the lateral (outside) surface rather than the front or inner thigh.
The Ventrogluteal (Hip)
The ventrogluteal site is on the side of your hip, over the gluteus medius muscle. It’s located using a specific hand placement: you place your palm on the bony bump at the top of the thigh bone (the greater trochanter), point your index finger toward the front of the hip bone, and spread your middle finger back toward the top of the hip crest. The injection goes into the center of the V-shaped triangle formed between those two fingers.
This site has a thick layer of muscle with relatively little overlying fat, which means the medication reliably reaches muscle tissue. Like the vastus lateralis, it can handle up to 5 mL of fluid. Many nursing guidelines now recommend the ventrogluteal site as the preferred option for adult IM injections that aren’t vaccines, particularly for medications that need to be deposited in a large muscle. The main drawback is that it’s harder to locate than the deltoid or thigh, and it usually requires someone else to administer the injection.
The Dorsogluteal (Buttock)
The dorsogluteal site, the upper outer quadrant of the buttock, was once the default location for IM injections. It has largely fallen out of favor. The sciatic nerve, the largest nerve in the body, runs through the buttock, and injections placed too far toward the center or too low carry a real risk of hitting it. Sciatic nerve injury from IM injection can cause severe, lasting pain, numbness, or even partial paralysis of the leg.
The sciatic nerve is the most commonly injured nerve from IM injections precisely because the buttock has been used so frequently. Current guidelines generally recommend choosing one of the other three sites instead. When the dorsogluteal site is used, precise placement in the upper outer quadrant is critical.
How Age and Body Size Affect Site Choice
For newborns and infants up to 12 months, the anterolateral thigh (vastus lateralis) is the standard site. Their deltoid muscles are simply too small to serve as a reliable target. Toddlers aged 1 to 2 can receive injections in either the thigh or the deltoid, depending on their muscle development. By school age and into adolescence, the deltoid becomes the primary site for vaccines, while the thigh and ventrogluteal sites are used for larger-volume medications.
Body weight also matters, mostly because it determines needle length. The needle needs to be long enough to pass through the skin and any subcutaneous fat to reach the muscle. The CDC recommends a 1-inch needle for adults weighing up to about 152 pounds. For men between 152 and 260 pounds, or women between 152 and 200 pounds, a 1- to 1.5-inch needle is appropriate. Adults above those weights generally need a 1.5-inch needle to ensure the medication reaches muscle tissue. The standard gauge for all ages is 22 to 25, with higher numbers meaning thinner needles.
Technique Tips That Reduce Pain
If you’ve ever been told to expect the provider to “pull back” on the syringe before injecting, that step has been dropped from current guidelines. The CDC recommends injecting rapidly without aspiration. Studies found that the old practice of aspirating increased pain because the needle stayed in the tissue longer and had more time to move around. No major blood vessels sit close enough to any of the recommended injection sites to make aspiration necessary.
Other evidence-based strategies for reducing pain include applying a topical numbing cream before the injection, breastfeeding infants during vaccination, and offering young children a sweet-tasting liquid by mouth during the procedure. For adults, relaxing the target muscle helps. If you’re receiving an injection in the deltoid, let your arm hang loosely at your side. For the thigh, sit with your leg relaxed and your foot flat on the floor.
Choosing a Site for Self-Injection
If you’re self-administering an IM medication (such as testosterone, vitamin B12, or certain fertility drugs), the outer thigh is your best option. The middle of the vastus lateralis is the safest target zone, sitting away from the major artery that runs along the front border of the muscle and from the nerves that supply the quadriceps. Aim for the dead center of the outer thigh, midway between hip and knee.
The deltoid is a secondary option for self-injection if the volume is small (under 2 mL), but it’s harder to control the needle with your non-dominant hand while keeping the muscle relaxed. The ventrogluteal and dorsogluteal sites are difficult to reach on your own body and are not recommended for self-administration.