Intramuscular Injection

Written by Jacquelyn Cafasso
Medically Reviewed by George Krucik, MD, MBA on May 30, 2013

What are Intramuscular Injections?

An intramuscular injection is a technique used to deliver a medication deep into the muscles. This allows the medication to be absorbed into the bloodstream quickly. You may have received an intramuscular injection at a doctor’s office the last time you got a vaccine, like the flu shot.

What are Intramuscular Injections Used For?

Intramuscular injections are used to deliver drugs and vaccines. They are a common practice in modern medicine. Several drugs and almost all inactivated vaccines are delivered this way.

Intramuscular injections are used when other types of delivery methods are not recommended. These include oral (swallowed into the stomach), intravenous (injected into the vein), and subcutaneous (injected just under the layer of skin).

The speed of absorption is faster for intramuscular injection compared to subcutaneous injection. This is because the muscle tissue has a greater blood supply than the area just under the skin. Muscle tissue may also hold a larger volume of medication than subcutaneous tissue.

Intramuscular injection may be used instead of intravenous injection because some drugs are irritating to veins. Sometimes, a suitable vein cannot be located. It may be used instead of oral delivery because some drugs are destroyed by the digestive system when a drug is swallowed

How are Intramuscular Injections Administered?

Intramuscular injections are often given in the following areas:

  • deltoid muscle of the arm
  • vastus lateralis muscle of the thigh
  • ventrogluteal and dorsogluteal muscles of the buttocks

The uptake of drugs from the thigh is slower than from the arm. The thigh may be used when the other sites are not available or if a patient needs to administer the medication on their own while lying down. A ventrogluteal site such as the buttocks is the safest site for adults and children over seven months of age. It is deep and not close to any major blood vessels and nerves. The thigh is preferred for immunizations in children. The deltoid in the arm is the site most typically used for vaccines. It is rarely used for other medications because the volume of medication is too large.

All healthcare workers who administer intramuscular injections to patients should receive training and education on proper administration. Selection of the needle size and injection site depends on many factors. These include age, size of the patient, and volume of medication. An injection site should not be used if there is evidence of infection or injury at the site.

The medication is administered with a needle long enough to reach the muscle without penetrating the structures underneath.

The following general procedure may be used for intramuscular injections:

1)    The practitioner positions the patient in a way that is comfortable and keeps the muscles relaxed

2)    The site selected for injection is cleaned with an alcohol swab. The skin is allowed to air dry.

3)    The practitioner spreads out the skin of the selected site to isolate the muscle.

4)    The needle is inserted into the muscle at about a 90 degree angle.

5)    The syringe is often drawn back slightly to ensure that the needle has not penetrated a blood vessel.

6)    The vaccine is injected slowly into the tissue.

7)    The needle is withdrawn quickly and properly discarded.

8)    Light pressure is applied to the injection site using a dry cotton ball or gauze.

9)    The patient is monitored for a short time for swelling, bleeding, or allergic reactions.

What are the Complications of Intramuscular Injection?

Complications of intramuscular injections include:

  • abscess
  • hematoma
  • injury to blood vessels and peripheral nerves
  • pain at the injection site
  • tingling or numbness
  • infection
  • bleeding
  • allergic reaction

Many children often experience anxiety due to the use of needles and fear of pain. A nurse practitioner should use extra precautions around children to help ease the child’s worries and prevent injury.

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Show Sources

  • Administration of Medication: Intramuscular (2011). Fatima College of Health Sciences. Retrieved May 17, 2013 from
  • Hanson, D.J. (1963). Intramuscular Injection Injuries and Complications. The American Journal of Nursing, 63(4), 99-101.
  • IM injections: How’s your technique? (2006). Irish Nurses and Midwives Organisation (INMO).  Retrieved May 17, 2013 from
  • Vaccine Administration Guidelines (2010). Centers for Disease Control and Prevention (CDC). Retrieved May 17, 2013 from

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