Injection 101: Overview, Types, Common Uses & Risks

Learn about the 4 types of injection: intradermal, subcutaneous, intravenous and intramuscular injections, and what they are used for in Singapore.

by Elaine Francis, R.N.

What is an injection?

An injection is a way of administering a sterile liquid form of medication into tissues of the body beneath the skin, usually using a sharp, hollow needle or tube. Most people with access to healthcare services experience injections at some point in their lives, such as childhood immunisations or medical treatment. Injections are usually used for drugs which need to act quickly or do not absorb well in the digestive system.

Some medications can be given as long-acting injections, known as 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 serious problems. Hormonal contraceptives or some psychiatric medications may be given as depot injections.

Types of Injection

One of the ways we describe injections is by the route or the type of body tissue they are administered into. The most common types of injections are:

Subcutaneous Injection (SC)

Subcutaneous injections (also referred to as ‘subcut’, ‘sub-Q’, or ‘SQ’) are injections that deliver medication into the layer of fat just under the skin. These can be given with small, fine needles, and so are only minimally uncomfortable. Sometimes, repeated SC injections can cause small lumps that can be felt under the skin. These areas should be avoided when giving subsequent injections as the rate of absorption can be unpredictable.

Intramuscular Injection (‘IM’)

Intramuscular injections are injections into a muscle. They are traditionally given in the upper, outer quadrant of the buttock, but some intramuscular injections can also be given in the thigh or upper arm. Muscles are vascular – they have a good supply of blood vessels – which means that medications given into the muscle are absorbed quickly. Longer needles are sometimes necessary to reach a muscle, so IM injections may be more uncomfortable than subcutaneous injections.

Intravenous Injection (IV)

Intravenous injections deliver medication directly into a vein. Medications given via IV injections are usually done through a cannula to ensure that medication is administered into a patent vein and to avoid any leakage of medication into other tissues. Historically, IV injections were more commonly given directly by needle but the risk of improper administration is higher than with a fitted and flushed cannula. Furthermore, needles can’t be left in the vein for future medication administration, unlike a cannula. To fit a cannula for IV injection or infusion, a doctor or nurse uses a device where a soft plastic tube is introduced using a needle. The needle is then withdrawn and the plastic tube is left in the vein with an access port affixed to the skin.

Other less common forms of injectable medication administration include:

Intraosseous Injection (IO)

Intraosseous injections are usually used in emergencies where medication or fluids need to get into the bloodstream quickly and venous access is difficult or impossible. Sometimes when someone is unwell, their blood pressure drops and their peripheral blood vessels – those in the extremities such as arms and legs – constrict to encourage blood flow to the most important parts of the body. In a cardiac arrest situation, they may also have no pulse and poor blood flow through the normal venous access routes. It can become almost impossible to get quick access to a vein so an intraosseous cannula can be fitted as an alternative. 

A small cannula is screwed through the skin into the bone marrow, often in the bony part of the shin just under the knee. This allows quick and easy administration of emergency medications and large volumes of resuscitation fluids. Administration into bone marrow has several benefits over intravenous access in an emergency, as it is non-collapsible – the access point is unlikely to fail. However, fitting intraosseous access devices has a small risk of causing fractures or infections in the deep tissues or bone so it is normally only used in emergencies.

Intradermal Injection

These are injections given in between the layers of the skin. This route is usually used when a localised reaction is required, for example with some vaccinations, allergy testing, or tests to determine previous exposure to some infections. In general, people who are up-to-date with common childhood vaccinations have experienced an intradermal injection.

Common Uses of Injection

The most common injection people see outside of a hospital setting is probably an insulin injection for individuals with diabetes. Insulin administration at home is a subcutaneous injection and can be given into any reasonably central areas of subcutaneous fat – the lower abdomen or tops of thighs are usually ideal. Most other injections that can be expected to be given at home are also subcutaneous, such as certain blood thinners or fertility treatments.

Common Injection Sites

Intramuscular Injection

Intramuscular injections should be given into as large a muscle as possible but where there is little chance of damage to a larger blood vessel or a nerve. The upper outer quadrant of the buttock is the ideal place for IM injections. 

When IM injections are given, a Z-track technique is often used. This technique ensures that the injected medication does not escape the muscle. 

Here are the steps taken to perform an IM injection using a Z-track method:

  1. Using your non-dominant hand, firmly pull your skin in one direction, away from the injection site.
  2. Insert the needle into the injection site at a 90-degree angle to the skin.
  3. Slowly and gently depress the plunger to release the medication into your muscle. Continue holding your skin with your non-dominant hand.
  4. After all the medication is emptied from the syringe, remove the needle at the same angle that you inserted it.
  5. Release the skin that your non-dominant hand is holding on to and allow your skin to return to its original position.

The Z-track technique works because subcutaneous fat moves more easily than muscle. When the skin is released after the needle is removed, the pulled skin and tissue covers the puncture site in the muscle and stops the injected medicine from escaping from the muscle.

Subcutaneous Injection

Subcutaneous injections are often self-administered, so the most common sites used are those which people can easily reach themselves. Often, subcutaneous injections are done in the lower abdomen or the tops of our thighs, as the fat in these areas has good absorption rates. Individuals with diabetes can usually perform their own injections and many type 1 diabetics begin regularly checking blood sugars with a finger-prick test and self-administering their insulin fairly early in childhood.

Intravenous Injection

Normally, intravenous injections are only administered by trained healthcare professionals. They choose an injection site by identifying a good vein to place an IV cannula, often on the inside of the elbow (the ‘antecubital fossa’), forearm or hand. For individuals with hard-to-find veins, doctors or nurses will sometimes use an ultrasound machine to find a good vein. People who need frequent repeated intravenous injections, such as individuals who need extended courses of antibiotics or rounds of chemotherapy, can have longer-term ports fitted and they often go home with these devices.

Every individual is different, and your loved one has care needs that are unique. Oftentimes, one may need assistance in administering injections, especially in making sure that the dosage of medication is right as well as ensuring a safe usage.

To give your loved one the best care he/she deserves, we provide a free care consultation for you and your loved one, to ensure that they get a Care Professional that best suits their needs.

Potential Complications of Injections


Any procedure which involves puncturing the skin carries a small risk of introducing microbes into the body, so there’s always a risk of developing infections. This risk can be minimised with proper cleaning and the use of aseptic, no-touch techniques. Implanted access points such as venous cannulas should be monitored regularly for signs of infection and should have a maximum duration of use, usually three days. Localised infections in deeper tissues can create an abscess – a fluid or pus-filled chamber within the body – which may require antibiotics and surgical drainage.

Keeping the medications sterile before administration is an important part of the preparation and administration of injections, and helps reduce the risk of serious infections. Some medications come in sterile liquid form in glass or plastic vials, while others come as a powder which needs to be reconstituted with sterile water or saline. Every step of the process is done in a clean environment and all equipment used for injections is single-use and sterile when packaged.


Almost all medications carry a risk of an adverse reaction – this can range from a minor allergic reaction to anaphylaxis requiring emergency medical treatment. Most licensed medications should be relatively well tolerated by most people, but all medication carries its own list of possible side effects. 

Some medications are irritating to the injection site and may have localised redness, pain or swelling after administration. Intravenous drugs that are irritant to the vein may also cause inflammation of the vein.


Any sharp object puncturing the skin can be uncomfortable, but using the smallest possible needle and ensuring that any alcohol-based skin cleaner has fully evaporated before injecting should minimise pain. There is a small risk that intramuscular injections could hit a nerve and cause long-lasting damage, but when proper injection technique is used and injection sites are chosen carefully, the risk is minimal.

Administration Error

There is a small chance that an injection might accidentally be given into or leak into the wrong kind of body tissue. As muscles contain blood vessels, there is a chance that an intramuscular injection could be given into a vein. This possibility is reduced by drawing back with the syringe after insertion to check that no blood can be withdrawn. 

Medications given intravenously can leak out of the vein or a venous cannula can be misplaced, meaning that medication or fluids could leak into the space around the veins, the muscle or subcutaneous fat. This can cause the wrong dose of medication to be absorbed or can mean that absorption is unpredictable. Some drugs can be very irritating when leaked from a vein, and can even cause serious damage to the local area. Medications known to be irritant should be given in a dilute form or, ideally, only given into a large vein with good blood flow.

There is also a slim chance of unintentional intra-arterial injection of drugs – i.e. an injection that’s intended to be given into a vein is given into an artery. This can cause serious problems, but thankfully, is extremely rare.

Needlestick Injuries

Needlestick injuries are one of the most common occupational injuries sustained by healthcare professionals, and healthcare providers have policies and procedures in place to reduce the risk and govern actions taken following a sharps injury. Any sharp implements used either in preparation or administration of the medications are disposed of in dedicated rigid ‘sharps’ boxes to reduce the risk of needlestick injuries to everyone involved in the process. Individual healthcare providers will follow local policies on the proper disposal of sharps and clinical waste.

Being punctured by a needle which has been used by someone else carries a risk of transmitting blood-borne diseases like hepatitis, so most equipment used in injections is now single-use and packaged in sterile conditions.

How to Administer an Injection Safely

Safe and effective administration of injectable medicines is a skill that needs to be taught and then practised, whether as a healthcare professional or someone who is learning to administer medication to themselves or someone they care for. Learning about injection sites, techniques, and problems to watch out for is important for everyone. Whatever the medication or route, with injections, cleanliness is always key.

Hand Hygiene

Good hand hygiene and maintaining a clean environment is paramount. Clean or sterile surgical gloves should be worn for IM injections or where an injection is given by a healthcare worker. Healthcare workers should also wear other personal protective equipment as appropriate – this may include aprons and masks.

People who routinely self-administer subcutaneous injections may choose not to wear gloves, but should still observe good hand hygiene practises.

Medication Preparation

Medications should be prepared in clean conditions using a no-touch technique and using sterile, single-use equipment. All medications to be injected should be checked for form and dosage, and to ensure they are in date and do not appear contaminated or discoloured. Different injectable medicines have different storage requirements and preparation techniques, and instructions should be carefully followed.

Skin Preparation

Special skin cleaning is not usually considered necessary for subcutaneous injections but is recommended for deeper injection sites. Where the skin needs to be cleaned, a sterile, single-use swab designed for medical skin cleansing should be used.

Giving the Injection

Most physically able people can learn to give subcutaneous injections themselves. The fine needles used for SC injections are usually not too uncomfortable, and most people report that the anticipation of sticking a needle into yourself is the worst part.

If a doctor or nurse is administering an injection, they have a responsibility to ensure that they have the right person – usually asking for more than one identifier, such as name and date of birth – the right drug, the right route, and the right dose at the right time. They should also explain what they’re doing and make sure their patient understands what is happening and gives their consent based on adequate information. A prescription for a medication includes the name of the medication, dose, and route, i.e. the way the drug is given, such as SC, IM, or IV.

After the Injection

It is also important to wash your hands after you administer an injection and remove your gloves. Needles should never be resheathed but should be immediately disposed of in a designated sharps box, which should ideally be within easy reach after giving the injection. Watch out for any reactions or side effects, especially if it’s the first time someone has had a medication. Injections which contain common allergens should ideally only be given where there are resources to quickly treat a bad reaction.

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Injections at Home

Some people have to inject themselves regularly in day-to-day life. People who have to have a course of injected blood thinners to treat blood clots typically need subcutaneous injections daily, and some fertility treatments involve injections at home. Insulin-dependent diabetics may have to inject themselves with a combination of short-, medium-, and long-acting insulins, possibly several times a day. Additionally, the amount of insulin injected may also need to be adjusted depending on a person’s blood sugar or the food they eat that day.

Some people may find it difficult to judge variable doses, and others may not be able to inject themselves for various reasons. Different types of insulin administration devices are available to make it easier for people to inject themselves, such as devices which click loudly as the dosage is set to enable people with sight impairment to safely choose the correct dose. People with reduced dexterity, such as those with arthritis, Parkinson’s, tremor, or injuries to the hands can choose devices designed to be accessible for those with mobility and dexterity issues.

Nevertheless, individuals may need assistance with injections at home for whatever reason. Administration of injections is a common reason for arranging home visits by caregivers or nurses. Experienced nurses can help to work out the appropriate dosage, administer routine injections and help with other medication and healthcare needs. 

30% of over-60s in Singapore have diabetes, and having good blood sugar control can make a serious difference to their health. If you need professional support with injections or other nursing procedures at home, Homage’s Nurses can help. Private nurses with specialist training in diabetes can assist with regular blood sugar checks, insulin and other medication administration, and healthy lifestyle support.Homage's trained and professional private nurses, who can help with home care and home nursing needs in Singapore, such as tube, stoma, and wound care in the comfort of home.

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About the Writer
Elaine Francis, R.N.
Elaine Francis is a registered nurse with 17 years’ experience in healthcare. She turned to writing to follow her passion for realistic medical communication. She loves translating medical jargon into accessible language for the people who need to understand it most. When she’s not writing or working on a busy cardiology unit, she spends her time telling her children to hurry up.
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