• What is an Injection?

What is an Injection?

An injection involves the administration of a medicine into tissues of the body, using a needle and syringe. Injections may be used to give drugs which would be destroyed by stomach acid if they were taken by mouth, or when a rapid onset of action is required (in the case of intravenous and subcutaneous injections, see below).

The three most commonly used types of injections are:

Subcutaneous injection (SC)

Subcutaneous means ‘under the skin’ and a short needle is used to inject a drug into the tissue layer between the skin and the muscle. Only small volumes of a drug (1ml) can be given this way but due to large amount of blood vessels around this area the dose is rapidly and reliably absorbed into the system. The usual injection sites are the upper arm, abdomen and front of the thigh.

Insulin and some hormones are often administered as subcutaneous injections.

Other drugs that need to be given very quickly can also be given with a subcutaneous injection such as epinephrine in an automated injector form, used to quickly treat severe allergic reactions.

Intravenous Injection (‘IV’)

An intravenous injection is used to deliver medication directly into a vein and therefore the blood directly.  This means that they will be rapidly transported around the body. Medications given via IV injections are usually done through a cannula (permanent access point) to ensure that medication is administered into an open vein and to avoid any leakage of medication into other tissues. An IV injection means that a medication may be given very slowly or very quickly, depending on the medical situation. Medications which may be given IV include chemotherapy, analgesics and antibiotics. 

Intramuscular Injection (‘IM’)

Intramuscular injections are injections given into a muscle. They are usually administered in the buttock, the thigh or upper arm. Medicines are absorbed less quickly from the muscles than SC or IV. Muscle tissue can also hold a larger volume of medication than subcutaneous tissue and up to 4ml can be given via this route.

Some medications can be given as long-acting injections, called depot injections. An amount of slow-release medication is injected and steadily absorbed into the body over a number of weeks or even months. Depot injections are only available for specific medications but can be helpful for people who find it difficult to remember to take their medication, or for situations where a missed dose could cause medical problems. Depot injections are frequently administered IM.

Some hormonal contraceptives and some psychiatric medications may be given as depot injections.