Injections deliver liquid medications, fluids, or nutrients directly into a person’s body. Different types of injections include intravenous, intramuscular, subcutaneous, intraosseous, and intradermal.

A healthcare professional can use injections, also known as shots, to administer vaccines and other types of medications into a person’s vein, muscle, skin, or bone.

Several different types of injections exist, depending on the purpose of the medication or substance in the shot.

A healthcare professional can inject many medications into many parts of the body. They will decide the most appropriate route of access depending on the situation.

Most injections consist of a needle and syringe. A doctor may also use a newer device, such as auto and jet injectors.

This article will discuss the different injection types and what a person can expect when receiving an injection.

A person who just had an intramuscular injection to deliver a vaccine.Share on Pinterest
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Healthcare professionals use intravenous (IV) injections to give medications directly into a vein. Because a person directly injects the medication into the bloodstream, it allows for rapid absorption, according to 2015 research. This causes an immediate response, per a 2019 review of the literature.

A medical professional can administer IV medications as a single dose or as an infusion over a period of many hours.

They may use an intravenous injection to:

  • administer fluid solutions and electrolytes to a person experiencing dehydration
  • give local and general anesthesia to people having surgery or a procedure
  • administer pain medications to a person in the emergency room or after surgery
  • give blood or blood products to a person
  • administer nutrition to a person who is severely malnourished
  • administer iron to a person with a severe iron deficiency
  • administer contrast dye to a person having a special imaging test
  • administer a steroid such as dexamethasone
  • give chemotherapy to a person with cancer
  • infuse monoclonal antibodies for COVID-19 treatment

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

  • the back of the hands
  • the front and back of the lower arm
  • the front elbow pit

Doctors may use veins in the foot to administer IV injections to infants who have not started walking yet, according to 2016 practice standards of the Infusion Nurses Society.

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.

Common uses for intramuscular injections may include:

  • administering most vaccines, per the Centers for Disease Control and Prevention (CDC)
  • administering select antibiotics, such as penicillin and streptomycin
  • giving corticosteroids for inflammation or allergic reactions
  • administering hormones, such as testosterone and medroxyprogesterone
  • administering drugs to patients who cannot take medications 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 upper outer thigh area muscle
  • the shoulder muscle and upper arm
  • the hip

Doctors administering intramuscular injections avoid injecting into a patient’s buttock area to prevent possible damage to the sciatic nerve, per a 2014 review.

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

Unlike muscle tissue, subcutaneous tissue has few blood vessels, according to a 2017 study. The presence of fewer blood cells allows the body to absorb the medication slowly over a period of time.

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

Common uses for subcutaneous injections may include the administration of:

Individuals with a blood clotting disorder should receive vaccines through 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 use a special needle to puncture the bone marrow in order 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, when intravenous access proves difficult or impossible, according to a 2016 systematic review.

Healthcare professionals use intraosseous injection as the quickest way to give fluids, drugs, and blood products to patients in many emergency situations, such as:

  • severe injuries from an accident or fall
  • electrocution
  • a medication overdose
  • childbirth complications
  • respiratory distress
  • prolonged or back-to-back seizures
  • accidental poisoning
  • insulin shock
  • stroke
  • cardiac arrest
  • administering medications to a patient in septic shock
  • local anesthesia delivery for individuals undergoing complex dental procedures, such as a root canal
  • dispensing pain medication to terminally ill patients

Common intraosseous injection sites include:

  • the lower leg bone
  • the thigh bone
  • the upper arm bone

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

Healthcare professionals give intradermal injections just below the surface of the skin, creating a small bump called a bleb or wheal. The intradermal injection route has the longest absorption time of all the different types of injections, according to a guide to clinical procedures published in 2015.

Common uses of intradermal injections may include:

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

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

However, less common adverse effects and risks come with all types of injections. These may include:

  • persistent or severe pain at the injection site
  • redness, swelling, warmth, or signs of infection
  • an abscess or collection of pus at the injection site
  • damage to underlying tissues
  • injury to adjacent 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 a person who has the virus.

To help prevent injection complications, the CDC has a summary page for healthcare personnel regarding the safe use of needles, syringes, and injectable medications in patient care settings.

People commonly use injected medicines in healthcare and home settings for the prevention, diagnosis, and treatment of various illnesses.

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

Typical injection side effects involve pain, swelling, or redness at the injection site. Side effects usually go away within a few days.

When doctors use the correct technique and injection site, injection complications, particularly with vaccines, happen rarely.