What to know about different types of injections

Intravenous injections 

Healthcare professionals use intravenous (IV) injections to give medications directly into a vein. Because this type of injection delivers medication into the bloodstream, it allows for rapid absorption, which causes an immediate response.

A medical professional can administer IV medications as an injection or as an infusion (a slow injection over a longer period of time).

They may use IV injections or infusions for purposes such as:

• providing fluid solutions and electrolytes to a person who is experiencing dehydration
• delivering local or general anesthesia before surgery or another procedure
• administering pain medications in the emergency room or after surgery
• giving someone blood or blood products
• providing nutrition to a person who is severely malnourished
• delivering iron to someone with a severe iron deficiency
• injecting contrast dye before a special imaging test
• giving a steroid such as dexamethasone
• administering chemotherapy to a person with cancer
• infusing monoclonal antibodies for COVID-19 treatment

Common IV injection sites — areas where veins lie close to a person’s skin — include:

• the backs of the hands
• the fronts and backs of the lower arms
• the front elbow pits

When giving IV injections to infants, doctors may use veins in the foot or the scalp.

Intramuscular injections 

Doctors can use intramuscular injections to deliver medication into a person’s muscle tissue. The muscles have a rich blood supply, which helps the body absorb the medication quickly.

Healthcare professionals commonly use intramuscular injections to administer:

• most vaccines, per the Centers for Disease Control and Prevention (CDC)
• select antibiotics, such as penicillin and streptomycin
• corticosteroids for inflammation or allergic reactions
• hormones, such as testosterone and medroxyprogesterone

Additionally, healthcare professionals may use this type of injection to administer medications to people who cannot take medication through other commonly used routes.

People with certain conditions, such as multiple sclerosis, may need to give themselves this type of injection at home. The recommended intramuscular injection sites include:

• the muscle of the upper outer thigh
• the shoulder muscle and upper arm
• the hip

Doctors avoid giving intramuscular injections into a person’s buttock area because doing so may cause damage to the sciatic nerve.

Subcutaneous injections 

Healthcare professionals administer subcutaneous injections into the fatty tissue just under the skin and above the muscle tissue. They will use a smaller needle to give subcutaneous injections to ensure that the medication enters the fatty tissue and not the muscle.

Unlike muscle tissue, subcutaneous tissue has few blood vessels. This means the body can absorb the medication slowly over a period of time.

Subcutaneous injections are less painful and less likely to cause an adverse reaction such as an infection.

People commonly receive the following medications as subcutaneous injections:

• insulin for diabetes
• blood thinners, such as heparin
• the measles, mumps, and rubella (MMR) and chickenpox (varicella) vaccines
• palliative care pain medications, such as fentanyl and morphine
• other home-administered drugs, such as Dupixent and fertility medications

Anyone who has a blood clotting disorder should receive vaccines via subcutaneous injection.

Common subcutaneous injection sites include:

• the outer side or back of the upper arm
• the front and outer side of the upper thigh
• the belly area

Intraosseous injections 

Intraosseous injections involve using a special needle to puncture the bone marrow to reach the veins. The bone marrow has a rich blood supply that connects straight to the circulatory system.

Healthcare professionals typically reserve intraosseous injections for emergencies in which IV access is difficult or impossible.

An intraosseous injection is the quickest way to administer fluids, drugs, and blood products in many emergency situations, such as:

• severe injuries from an accident or fall
• electrocution
• medication overdose
• childbirth complications
• respiratory distress
• prolonged or back-to-back seizures
• accidental poisoning
• insulin shock
• stroke
• cardiac arrest
• septic shock

Healthcare professionals can also use this type of injection to deliver local anesthesia to people undergoing a complex dental procedure, such as a root canal, or to dispense pain medication for palliative care if IV access is not possible.

The following bones are common intraosseous injection sites:

• lower leg bone
• thigh bone
• upper arm bone

Intraosseous injection is an effective route for emergency vein access in all age groups.

Intradermal injections 

Healthcare professionals give intradermal injections just under the surface of the skin, where a small bump called a bleb or wheal will form after the injection. The intradermal injection route has the longest absorption time of all the types of injections.

Common uses of intradermal injections include:

• allergy testing
• tuberculosis (TB) screening
• administration of the influenza vaccine Fluzone Intradermal

Healthcare professionals most commonly use body parts with little hair as intradermal injection sites. Examples include the inner surface of the forearm and the upper back, under the scapula. Additionally, the injection site should have no sores, rashes, moles, or scars.

Side effects and risks

Any injection or vaccine can cause side effects. For the most part, these effects are minor, such as a sore arm or a low grade fever. Minor side effects typically go away within a few days, according to the CDC.

Less commonly, all types of injections may cause adverse effects and pose certain risks, such as:

• persistent or severe pain at the injection site
• skin discoloration, swelling, warmth, or other signs of infection
• an abscess (a buildup of pus under the skin at the injection site)
• damage to underlying tissues
• injury to nearby nerves
• bone injury or infection
• excessive bleeding, especially in people with bleeding disorders
• formation of a large blood clot at the injection site
• an allergic reaction
• nausea, vomiting, or dizziness
• fainting

Transmission of an infectious disease such as hepatitis C could also occur if a person comes into contact with the blood of someone who has the virus.

To help prevent injection complications, the CDC provides guidance for healthcare professionals about the safe use of needles, syringes, and injectable medications in healthcare settings.

Summary

People commonly receive injected medications in healthcare settings or inject medications at home to help prevent and treat various health conditions.

Healthcare professionals can use injections to deliver vaccines and other medications into a person’s vein, muscle, skin, or bone.

Typical injection side effects include pain, swelling, and skin discoloration at the injection site. These side effects typically go away within a few days.

Injection complications, particularly with vaccines, are rare as long as healthcare professionals use the correct technique and injection site.