Intramuscular (IM) injections are given into four main sites on the body: the deltoid muscle of the upper arm, the vastus lateralis muscle of the outer thigh, the ventrogluteal site on the side of the hip, and the dorsogluteal site in the upper buttock. The right site depends on the patient’s age, body size, and the volume of medication being injected. Here’s how to find each one and when each is used.
The Deltoid (Upper Arm)
The deltoid is the most familiar injection site. It’s the muscle on the outside of your upper arm, and it’s where most vaccines are given to older children and adults. The correct spot is not at the top of the shoulder, which is a common mistake. A cadaveric study published in Cureus found that the safest point is about four fingerbreadths, or 9 centimeters, below the bony point at the top of your shoulder (the acromion). This keeps the needle well clear of the axillary nerve and a major artery that run roughly 8 centimeters below that bony landmark.
To help position the muscle correctly, the person receiving the injection can place their hand on their hip, which opens the shoulder to about 60 degrees and exposes the thickest part of the muscle. The deltoid is a relatively small muscle, so it can only handle between 0.5 and 2 mL of fluid in adolescents and adults. Most standard vaccine doses (0.5 mL) fit well here, but larger-volume medications need a bigger site.
The Vastus Lateralis (Outer Thigh)
The vastus lateralis sits on the front and outer part of the thigh. It’s the preferred site for infants and children under two years old because babies haven’t developed enough deltoid muscle mass yet. The CDC recommends targeting the middle third of the muscle, which falls between two landmarks: the greater trochanter (the bony bump you can feel at the top of your outer thigh near the hip) and the lateral condyle (the bony bump just above the outer knee).
In adults, the vastus lateralis can accept up to 5 mL of fluid, making it useful when larger medication volumes are needed. For infants, the maximum is 0.5 mL. This site is also practical for self-injection because it’s easy to see and reach without help.
The Ventrogluteal Site (Side of the Hip)
The ventrogluteal site is on the side of the hip, not the buttock. Many nurses and clinical guidelines now consider it the safest site for IM injections in adults because the area has thick muscle, no major nerves or blood vessels nearby, and a relatively thin layer of fat. It also allows better absorption of medication compared to other gluteal sites.
To locate it, the person giving the injection places the heel of their hand on the greater trochanter (the bony prominence on the outer hip) and spreads their index and middle fingers to form a V shape pointing toward the hip bone. The injection goes into the center of that V. This site can handle up to 5 mL in adults. In infants older than seven months, it can accept up to 1 mL, and up to 1.5 mL in toddlers.
The Dorsogluteal Site (Upper Buttock)
The dorsogluteal site is in the upper outer quadrant of the buttock. While it was once the most commonly used IM site, many health organizations now discourage it because of the risk of hitting the sciatic nerve. The sciatic nerve is the largest nerve in the body, and it runs through the buttock region. An injection placed too far toward the center or too low can damage it, causing problems that range from numbness and weakness to severe, lasting pain or even paralysis of part of the leg.
Sciatic nerve injury from misplaced gluteal injections remains a problem worldwide. If this site must be used, the injection should stay firmly in the upper outer quadrant. However, the ventrogluteal site offers the same large muscle volume (up to 5 mL in adults) without the nerve risk, which is why it’s now the preferred alternative.
Which Site for Which Age
- Newborns (28 days and younger): Vastus lateralis only. A shorter needle (5/8 inch) is used because of their small muscle mass.
- Infants 1 to 12 months: Vastus lateralis, using a 1-inch needle.
- Toddlers 1 to 2 years: Vastus lateralis is still preferred. The deltoid can be used if the muscle is large enough, with a shorter needle (5/8 to 1 inch).
- Children 3 to 10 years: Deltoid for most vaccines. The vastus lateralis is an alternative, especially for larger volumes.
- Adolescents and adults: Deltoid for vaccines and small-volume injections. Ventrogluteal or vastus lateralis for larger volumes.
Needle Length by Body Size
For IM injections to work properly, the needle must reach the muscle and not stop in the fat layer above it. The CDC provides specific needle-length recommendations based on weight for adult deltoid injections:
- 130 lbs (60 kg) or less: 1-inch needle
- 130 to 152 lbs (60 to 70 kg): 1-inch needle
- Men 152 to 260 lbs, women 152 to 200 lbs: 1 to 1.5-inch needle
- Men over 260 lbs, women over 200 lbs: 1.5-inch needle
All IM injections typically use a 22- to 25-gauge needle. A higher gauge number means a thinner needle, so a 25-gauge needle is thinner and generally less painful than a 22-gauge.
Technique Tips That Reduce Pain and Complications
Aspiration, the old practice of pulling back on the syringe plunger before injecting to check for blood, is no longer recommended for vaccines. The CDC notes that no large blood vessels exist at any of the standard injection sites, and the extra step of aspiration can actually increase pain, particularly in infants.
The Z-track technique is sometimes used for medications that can irritate tissue, such as certain anti-inflammatory drugs. The person giving the injection pulls the skin to one side before inserting the needle, then releases it after withdrawing. This creates a zigzag path through the tissue that seals the medication inside the muscle and prevents it from leaking back into the layers above. Research has shown this method reduces both pain and drug leakage compared to the standard approach.
For any IM injection, the needle enters the skin at a 90-degree angle, perpendicular to the surface. The skin should be stretched taut rather than pinched (pinching is for subcutaneous injections, which target the fat layer). Injecting the medication slowly, over several seconds, also helps reduce discomfort and allows the muscle to absorb the fluid more gradually.