Medications and Pharmacology: Why do they inject in the buttocks?

October 7, 2025 •

3 min read

The gluteal muscles are among the body’s largest, capable of accommodating significantly larger volumes of medication (up to 5ml) compared to other injection sites. This substantial size and rich blood supply are the primary reasons why do they inject in the buttocks, ensuring effective and rapid delivery of certain medications directly into the bloodstream.

Quick Summary

This article explains the anatomical advantages of using the gluteal muscles for intramuscular injections, detailing the safest injection sites and why larger or more viscous medications are administered this way. It also covers the absorption process, benefits, and potential risks associated with the procedure.

Key Points

Anatomical Advantages: The large gluteal muscle mass allows for rapid absorption and larger medication volumes, up to 5 mL.
Safety Through Site Selection: The ventrogluteal area (hip) is the safest site, as it avoids major nerves and blood vessels, unlike the older dorsogluteal method.
Mechanism of Action: Intramuscular injections bypass the digestive system, ensuring a high concentration of the drug reaches the bloodstream for faster, more potent effects.
Long-Acting Formulations: Depot injections, designed for slow, sustained release over weeks or months, are frequently administered into the deep gluteal muscles.
Risk of Subcutaneous Injection: Injecting into fat instead of muscle, especially in overweight individuals, can delay absorption and increase the risk of complications.
Medication Types: The gluteal site is ideal for viscous or irritating medications, such as certain antibiotics and hormone replacement therapies.

The Anatomy Behind Intramuscular Injections

Intramuscular (IM) injections deliver medications deep into muscle tissue for rapid absorption into the bloodstream. The choice of injection site affects both safety and drug absorption. The buttocks are a preferred site for certain medications due to the large gluteal muscles, including the gluteus maximus and gluteus medius. This large muscle mass and rich blood supply facilitate the dispersion and absorption of medication, especially for large volumes, viscous substances, or those irritating to tissue. By avoiding the digestive system, IM injections also bypass first-pass metabolism in the liver, leading to more potent and predictable drug levels in the body.

The Ventrogluteal Site: The Modern and Safer Choice

The dorsogluteal site (upper-outer buttock) was traditionally used. However, its proximity to the sciatic nerve and major blood vessels poses a risk of nerve injury and other complications. Studies have also shown that dorsogluteal injections, particularly in women, may end up in subcutaneous fat rather than muscle, hindering absorption.

For improved safety, the ventrogluteal site on the side of the hip is now recommended for adults and walking children. This area, involving the gluteus medius and minimus, is free from major nerves and vessels and offers a consistent muscle depth. A specific V-shape technique helps accurately locate this site, reducing the risk of complications.

Medications and Formulations Administered in the Gluteal Muscles

The gluteal muscles are suitable for medications requiring slow, sustained release, such as long-acting injectables (LAIs) or depot injections. These formulations are designed for slow absorption from muscle over weeks or months. Other medications commonly injected into the gluteal muscles include:

Hormone Therapies: Testosterone, often in an oil suspension for slow absorption.
Certain Antibiotics: Large-volume or viscous antibiotics like penicillin G benzathine.
Long-Acting Antipsychotics: Depot formulations for conditions like schizophrenia.
Vitamin Supplements: Vitamin B12 for deficiency.

Benefits of Gluteal Intramuscular Injections

Using the gluteal muscle for injections offers several advantages:

Higher Volume Capacity: Can accommodate up to 5 mL of medication.
Less Pain and Irritation: Muscle tissue disperses viscous or irritating medications, reducing discomfort.
Reliable Absorption: Rich blood supply ensures consistent and predictable absorption.
Improved Compliance: Beneficial for long-acting depot medications, aiding patients who might struggle with daily oral medication.

Potential Complications and Risks

While generally safe, especially with the ventrogluteal site, improper technique can lead to complications. Potential risks include:

Sciatic Nerve Injury: A risk associated with the outdated dorsogluteal site.
Injection into Subcutaneous Fat: Can delay absorption and increase local side effect risk.
Injection Site Reactions: Common side effects include pain, swelling, and bruising.
Needle Length Issues: A standard needle may be too short in individuals with more body fat, requiring a longer needle for effective IM injection.

Comparison of Common Intramuscular Injection Sites


Feature	Ventrogluteal (Buttock)	Deltoid (Upper Arm)	Vastus Lateralis (Thigh)
Maximum Volume	Up to 5 mL	Up to 2 mL (typically ≤ 1 mL)	Up to 3 mL
Muscle Mass	Large and well-developed in most adults	Small to moderate	Large and well-developed, especially in children
Safety	High (avoids major nerves and vessels)	Moderate (risk of nerve/artery injury with poor landmarking)	High (avoids major nerves and vessels)
Common Use Cases	High-volume, viscous, or irritating medications; long-acting depots	Small-volume vaccinations	Children under 3; self-administration; larger volumes than deltoid
Technique	Requires proper landmarking (V-shape)	Careful landmarking needed (2-3 fingerbreadths below acromion)	Middle third of the thigh

Conclusion

The buttocks are chosen for injections due to their large muscle mass, which facilitates rapid and efficient absorption of larger volumes and minimizes irritation from viscous medications. The modern and safer ventrogluteal site is preferred over the older dorsogluteal site, which carried risks of nerve injury. The selection of an injection site is a clinical decision based on the specific medication, dosage, and patient, with the buttocks remaining a crucial option for many effective treatments. For regular IM treatments, rotating injection sites is important to prevent tissue damage.

Frequently Asked Questions

While the arm (deltoid muscle) is a common injection site, its muscle mass is smaller and can only accommodate smaller volumes of medication, typically 1 to 2 mL. For larger volumes or certain viscous drugs, a larger muscle like the gluteus is required for safe and effective absorption.

Compared to smaller muscles, the large muscle mass of the buttocks can sometimes make injections less painful because the muscle tissue better disperses the medication. The pain experienced often depends on the medication's viscosity, the injection technique, and the patient's individual sensitivity.

The dorsogluteal injection site is in the upper outer quadrant of the buttock, a location now considered less safe due to the risk of hitting the sciatic nerve. The ventrogluteal site is on the side of the hip, identified by a specific V-shape landmarking technique, and is the safer, modern preference.

The Z-track technique involves pulling the skin and subcutaneous tissue laterally before injection. This creates a zigzag path that seals the medication within the muscle after the needle is withdrawn, preventing leakage into the subcutaneous tissue and reducing irritation. It is often used for gluteal injections with irritating or staining medications.

Yes, if not administered correctly. This is a significant risk with the outdated dorsogluteal method due to the proximity of the sciatic nerve. Using the proper ventrogluteal site and correct technique drastically minimizes this risk.

The ventrogluteal site is considered safe for children older than 7 months. However, the thigh (vastus lateralis) is often the preferred site for children under 3 years old, as their gluteal muscles are less developed.

Injections into the muscle (intramuscular) are necessary for medications that need rapid absorption, are given in larger volumes, are more viscous, or are formulated for long-acting, slow release (depot injections).