What is an Intramuscular Injection?

Mary McMahon

An intramuscular injection is an injection which introduces medication directly into a muscle. From the muscle, the medication will travel to the rest of the body via the cardiovascular system. This method of medication delivery may be used for medications which cannot be given orally for various reasons or when rapid action is desired. Some examples of medications which can be delivered intramuscularly include: vaccines, antibiotics, steroids, pain management medications, and sex hormones.

The needle used in the injection should be disposed of in a well-marked sharps container.
The needle used in the injection should be disposed of in a well-marked sharps container.

Several sites can be used for intramuscular injections. The buttocks are a rather notorious location, but injections can also be given in the thigh, leg, and deltoid muscles. The selection of an injection site depends on a number of factors. It is important to select an area with ample muscle padding, and many doctors also prefer to rotate intramuscular injection sites, especially if a patient needs multiple injections. Some injections are more likely to cause bruising and pain than others, which can influence the choice of a site, and some doctors have a personal preference.

Intramuscle injection introduces medication directly into a muscle.
Intramuscle injection introduces medication directly into a muscle.

The technique involved in an intramuscular injection is easy enough that people can do it at home. Home treatment for certain conditions can involve the administration of medication intramuscularly, with the patient doing the injections personally or a care provider performing the injections if the patient is unable to. Learning the procedure takes a few minutes in the office of a nurse or doctor, and most people become adept very quickly.

Many medications are injected intramuscularly.
Many medications are injected intramuscularly.

A clean, sterile needle is used for an intramuscular injection. Medication is drawn up into the body of the needle from a vial or ampule, the site of the injection is sterilized, and the needle is introduced to the site. People who need to perform intramuscular injections are usually shown how to hold and insert the needle to reduce pain and ensure that the medication ends up in the desired location. They are also trained to select a needle of the correct size for the medication. It's important that the barrel can hold the required dose safely, and that the bore of the needle used will accommodate the medication if it is viscous.

Once an intramuscular injection is complete, the needle is disposed of in a sharps container, and the site of the injection may be bandaged in case it bleeds a little bit, although this is not required. It is generally recognized as unsafe to reuse needles, even on the same patient, because they can acquire infectious material which could harm the patient, and because each use dulls the needle, which can make reuse of needles very painful.

A vial of medicine for an intramusular injection.
A vial of medicine for an intramusular injection.

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Discussion Comments


The bad part is when people just won't get an injection, even though that's what's best for them.

My husband got a terrible ear infection, and I finally bullied him into going to the ER (on New Year's Eve, no less) and the doctor diagnosed him with otitis media and said he needed a round of antibiotics, and wanted to get him kick-started with an injection. He absolutely refused.

As a result, he started with a pill and stayed sick longer. I really fussed at him about it, since the injection would have been in the backside and he never would have even seen the needle, but he was just intent on being stubborn. I hate needles too, but doggone it, sometimes, an injection is necessary! I told him the next time the doctor wanted to give him a shot, he was getting one -- period.


When I was about 20, there was a red measles outbreak on a college campus in my state. As a result, the state department of public health decreed that all college students who had not had a booster in 10 years had to have one before they would be allowed to register for the winter quarter.

I ended up on the wrong side of the 10-year mark and had to get the vaccine at the county health department. I had it in my arm and had a rather serious reaction to it. It didn't make me feel bad, but it made the injection site swell up like a spider bite! I went to my regular doctor and his opinion was the tech allowed some of the vaccine to get into the tissues. The swollen area was about the size of the palm of my hand! A benadryl helped, but that was a sore spot.

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