Subcutaneous injections are a method of administering medication just under the skin, between the fatty tissue and muscle. It allows medication to be absorbed slowly over a longer period of time.

During a subcutaneous injection, a short needle is used to inject a drug into the fatty tissue layer between the skin and the muscle, usually in specific areas of the thigh, arm, and abdomen.

Medication given this way is absorbed more slowly than if injected into a vein or taken by mouth (orally), sometimes over a period of 24 hours.

This means subcutaneous injections are often used when other administration methods might be less effective. For example, some medications can’t be given orally because acid and enzymes in the stomach would destroy them.

Other methods, like intravenous injection, can be difficult and costly. For small amounts of delicate drugs, a subcutaneous injection can be a useful, safe, and convenient method of getting a medication into your body.

Keep reading to learn more about the types of medications that can be administered subcutaneously, how to do it, and the possible benefits and risks.

Medications administered by subcutaneous injection include those that can be given in small volumes. This is usually less than 1.5 milliliters (mL), but up to 3 mL may be administered into the abdomen.

Some medications that are commonly administered subcutaneously include:

Other drugs that need to be given very quickly can also be administered via subcutaneous injection.

For instance, epinephrine comes in an automated injector form called an EpiPen, which is used to treat anaphylaxis quickly. While it’s intended to be given intramuscularly, epinephrine will also work if given subcutaneously.

Other drugs used to relieve pain, nausea, and vomiting, as well as anesthetics, can be administered subcutaneously.

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The location of injection is important for subcutaneous injections. The drug needs to be injected into the fatty tissue just below the skin.

Some areas of the body have a more easily accessible layer of tissue, where a needle injected under the skin will not hit muscle, bone, or blood vessels.

The most common subcutaneous injection sites are:

  • Abdomen: at or under the level of the belly button, about 1.5 inches away from the navel
  • Upper arm: back or side of the upper arm, about 3 inches above the elbow and 3 inches below the shoulder
  • Upper thigh: front or side of the upper thigh

If you’re self-administering your subcutaneous injection, this should be done in the abdomen or upper thigh only.

Before administering a subcutaneous injection, it’s important to make sure you have all of the necessary equipment:

  • Medication: Vials of liquid medication can be single-use or multiuse. Vials can also be filled with a powder to which liquid needs to be added.
  • Syringes: The needles are short, usually 4 to 8 millimeters (0.16 to 0.31 inches) long. The thickness of the needle is usually 25 to 30 gauge. There may be other options for doses more than 1 mL or for children or people with visual impairments.
  • Auto-injector pen: Some medications are available in a “pen” with a short, single-use needle screwed onto the end of a pen-shaped, multiuse vial. The amount of medication needed is then dialed in at the end.

There are several steps to follow when administering a subcutaneous injection. It’s important to practice proper hygiene to prevent possible infections.

Before the injection, it’s important to prepare to injection site. Here’s how to do this:

  1. Wash your hands: Wash your hands with soap and warm water, and thoroughly scrub between fingers, on the backs of hands, and under fingernails. Lather for 20 seconds — the time it takes to sing “Happy Birthday” twice.
  2. Gather supplies: Assemble the following supplies:
    • needle and syringe with medication or an auto-injector pen
    • alcohol pads
    • gauze
    • puncture-resistant container to discard the used needles and syringe (typically a red plastic “sharps” container)
    • bandages
  3. Inspect the injection site: Before injecting medication, inspect your skin to make sure there’s no bruising, burns, swelling, hardness, or irritation in the area. Alternate injection sites to prevent damage to an area with repeated injections.
  4. Clean the injection site: Clean the skin with an alcohol swab. Let the alcohol dry thoroughly before injecting to prevent stinging and ensure disinfection.

Preparing the syringe with medication

Now, it’s time to prepare the syringe with medication.

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Before withdrawing medication from a vial, make sure it’s the correct medication, at the correct dose, at the correct time, and in the right manner. Use a new needle and syringe with every injection.

1. Insert air into the vial

  1. Remove the cap from the vial: If the vial is multidose, note when it was first opened. The rubber stopper should be cleaned with an alcohol swab.
  2. Draw air into the syringe: Draw back the plunger to fill the syringe with air up to the dose that you’ll be injecting. This is done because the vial is a vacuum, and you need to add an equal amount of air to regulate the pressure, making it easier to draw the medication into the syringe.
  3. Insert air into the vial: Remove the cap from the needle and push the needle through the rubber stopper at the top of the vial. Inject all the air into the vial. Be careful not to touch the needle to keep it clean.

2. Withdraw the medication

Once the needle is in the vial and the air has been released from the syringe, it’s time to withdraw the medication.

Turn the vial and syringe upside down so the needle points upward. Then pull back on the plunger to withdraw the correct amount of medication.

3. Remove any air bubbles

While the needle is still in the vial, tap the syringe to push any bubbles to the top and gently depress the plunger to push the air bubbles out.

Preparing an auto-injector

If you’re using a pen delivery system for a subcutaneous injection, filling it with medication is slightly different from filling a syringe.

  • Attach the needle to the pen.
  • The first time you use the pen, you’ll need to prime it to push out extra air in the delivery system.
  • Dial a small dose (usually 2 units or 0.02 mL, or as indicated by the package instructions) and push the button to expel the primer.
  • Dial the correct dose and prepare for your injection.

Injecting the medication

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Now, it’s time to inject the medication.

  1. Pinch your skin: With the hand not holding the syringe, pinch a chunk of skin between your thumb and index finger, and hold it. This pulls the fatty tissue away from the muscle and makes the injection easier. (Your thumb and forefinger should be about 1.5 inches apart.)
  2. Inject the medication: Insert the needle into the pinched skin at a 90-degree angle, or 45 degrees if there is very little fat. You should do this quickly, but without great force.
  3. Deliver the medication: Slowly push the plunger to inject the entire amount of medication.
  4. Withdraw the needle: Let go of the pinched skin and withdraw the needle. Discard the used needle in a puncture-resistant “sharps” container.
  5. Apply pressure to the site: Use gauze to apply light pressure to the injection site. If there’s any bleeding, it should be very minor. You may notice a little bruising later. This is common and nothing to be concerned about.

If you administer subcutaneous injections regularly, such as once or multiple times daily, you will need to rotate the injection sites. This means that you shouldn’t inject medication into the same spot twice in a row.

For example, if you injected medication into your left thigh this morning, use your right thigh this afternoon, your left abdomen tomorrow morning, and your right abdomen tomorrow afternoon.

Using the same injection site over and over again can cause discomfort and even tissue damage.

It’s also important to keep track of where you inject the medication.

As with any injection procedure, some possible side effects and complications could arise.

The most common side effects affect the injection site, and may include:

If you experience any of these symptoms, it’s important to speak with a healthcare professional. They could assess your symptoms and develop an appropriate management plan.

Subcutaneous injections aren’t usually very painful because they use small needles. Most people feel a “pinch” when the needle goes in.

That said, severe pain has been reported by some people, especially when bigger needles or medication doses are used.

For subcutaneous injections, you’ll insert the full length of the needle, which is typically 4 to 8 millimeters (0.16 to 0.31 inches) long.

Research suggests that the abdomen may be the least painful place for a subcutaneous injection, but this may vary for each individual.

In some cases, subcutaneous injections may cause small, hard nodules or lumps to form beneath the skin.

Subcutaneous injections are a method of administering medications into the layer of fat that lies between the skin and muscle with a small needle.

It could be used for medications that help treat diabetes, high blood pressure, and chronic pain, among other conditions.

The most common side effects include mild pain, bruising, and swelling at the injection site. However, it’s possible to experience an infection, which can cause more severe symptoms.

Speak with a doctor if you’re unsure how to inject the medication. They can help you do it more confidently and safely.