Injection Supplies: How to Choose the Best Needle and Syringe Size for Your Prescription

Many medications today come as injectable products. This is requiring more and more people to give themselves injections at home to manage their health.

Administering injections requires some prep work, though. It’s important to know what supplies you’ll need. This may include choosing the correct needle and syringe sizes.

In this guide, we’ll discuss how to pick the right needles and syringes for your prescription. We’ll also cover why it’s important to talk to a healthcare professional (HCP) for personalized injection advice.

What supplies are needed to inject medication at home?

You’ll need several items to safely inject your medication at home. This includes:

• Your medication: This could be in a vial, prefilled syringe, or injection pen.

• Syringes and needles: These are used to fill up, hold, and inject the medication into your body. However, these aren’t necessary if you’re using an injection pen with a needle built in.

• Alcohol wipes: These are used to clean the top of the vial (if applicable) and the area of skin where you’ll be injecting the medication. This lowers the risk of infection.

• Gauze or cotton balls: After your injection, use these products to apply pressure to the injection site to stop any bleeding.

• Bandages: In addition to gauze or cotton balls, you can use a bandage to cover the injection site if there’s bleeding.

• Sharps container: Use a hard plastic container, such as a dedicated sharps container, laundry detergent bottle, or a bulk coffee grounds container, to safely dispose of used needles and syringes. 

It’s important to ensure you practice good hand hygiene during the injection process, too. Be sure to wash your hands or use hand sanitizer before and after your dose. This helps to prevent infection.

Do you need needles and syringes for injection pens?

You don’t need a syringe if your medication comes in an injection pen. This is because the medication is already inside the pen. But you may need something called a pen needle. This is a smaller-than-normal needle that connects directly to the pen.

Pen needles screw onto the end of injection pens. Medications such as Ozempic (semaglutide) come prepackaged with pen needles, while medications such as Lantus SoloStar (insulin glargine) and Victoza (liraglutide) need a separate prescription for them.

Be sure to check with your pharmacist to see if your injectable medication comes with pen needles or if you’ll need to purchase them separately. And know that if you want your pen needles to be covered by insurance, you’ll need to receive a prescription for them.

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Here’s what to know about needle sizes

Picking the right needle size can be intimidating. Here are some details to better understand the differences between sizes.

Needle gauge

Needle gauge, often listed as “G” on a product label, refers to the thickness of the needle and the size of the hole that the medication passes through. The higher the number, the smaller the hole. For example, a 25G needle is thinner and has a smaller hole than an 18G needle. Needle gauges range in size from 7G to 33G.

The ideal needle gauge is usually determined by the kind of medication you’re injecting. A lower (wider) gauge is usually needed when drawing up and delivering a relatively thick medication, such as testosterone cypionate. A higher (thinner) gauge is usually used for thinner medications, such as insulin.

Think of needle sizes like choosing a straw for your favorite drink. A higher gauge needle, such as a 30G or 32G needle, is comparable to a small coffee stirrer. On the other hand, a lower gauge needle, such as a 18G or 20G needle, mirrors a wide smoothie straw. So, picking the right gauge is like selecting the perfect straw for your drink — it helps the medicine flow smoothly.

Needle length

Needle length refers to the distance from the tip of the needle to where the needle attaches to the syringe or pen. Needle length is important depending on the kind of injection you’re using. Needle lengths range from 3/8 of an inch to 3.5 inches.

A subcutaneous injection needs a relatively short needle. This is because the medication is delivered just under the skin. An intramuscular (IM) injection needs a longer needle because the medication is delivered into the muscle. Our muscles live beneath our skin and fatty tissue, so this is why the needle needs to be inserted a little further.

Here’s what to know about syringe sizes

Choosing the right syringe size is usually based on your medication dose or the volume of liquid the injection requires. Syringes are usually labeled in milliliters (mL) or cubic centimeters (cc), with 1 mL equaling 1 cc. For insulin, syringes may be labeled in units, ranging in volume from 30 units (0.3 mL) to 100 units (1 mL).

Syringes come in many sizes. Some are as small as 0.3 mL, and others are as large as 60 mL. It’s important to try to pick the smallest syringe size that will hold your dose. Typically, IM and subcutaneous injections require a 0.3 mL to 3 mL syringe. There is some flexibility, though; you can usually switch sizes if your pharmacy is out of stock on your preferred size.

What size needle is best for intramuscular (IM) injections?

The most common needle size for IM injections is between 22G to 25G in width and 1 inch to 1.5 inches in length. The needle needs to be long enough to reach the muscle and wide enough to draw up and deliver the medication.

There are some other nuances to consider, though. Be sure to talk to your HCP to learn about the right needle gauge and length for you. Factors such as your prescribed medication, body size, and muscle mass will all help determine the best needle size for IM injections.

Here’s a quick summary for both kids and adults:

What size needle is best for subcutaneous injections?

Subcutaneous injections typically require shorter needles than IM injections. They often use 23G to 25G needles that are 5/8 of an inch long.

Needles used to deliver insulin are a little different. They’re even smaller in size. Most insulin products use 29G to 32G needles that are 5/32 (4 mm) to 1/2 of an inch (12 mm) long.

How to determine the right needle and syringe size for you

There are three main factors that will determine your ideal needle and syringe size. However, know that your HCP will make the final call on the sizes that are best for you.

1. Medication viscosity (thickness) determines the needle gauge

A wider needle with a lower gauge is recommended for medications that are thicker, or “high viscosity.” A thinner needle with a higher gauge is recommended for medications that are less thick, or “low viscosity.” Your pharmacist can guide you in the right direction for what to use.

For example, a low gauge needle is often used to transfer hormone therapy medications, such as progesterone in oil (a thicker medication), from the vial to the syringe. You may then switch the needle to a higher gauge for more comfort when injecting. Typically, this would be a 22G to 25G needle.

Another example is insulin. Insulin isn’t as thick as testosterone, so a higher gauge needle may be used.

2. Location and method of injection determine the needle gauge and length

Subcutaneous injections typically need shorter and thinner needles. IM injections typically need longer and thicker needles.

3. The amount of medication you’re injecting determines the syringe size

It’s important to pick the smallest size syringe that will hold your dose. This is important for accurate doses. Your medication should fill at least 20% of the syringe. For example, if you need to inject 2 mL of medication, you shouldn’t use a syringe that holds more than 10 mL.

Is it safe to reuse needles and syringes?

No, it’s not safe to reuse or share needles and syringes.

When needles are reused, they can become dull or damaged. This increases the risk of pain during administration. Bacteria on the needle can also grow with each use, increasing your risk for infection. It’s not safe to reuse syringes either, due to the risk of infection.

Make sure you always use a new, sterile needle and syringe with every dose.

Why trust our experts?

Written by:

Emily Nailor, PharmD Candidate

Emily Nailor, PharmD candidate, is a pharmacy intern with Walgreens. She is also a pharmacy intern with PharmScript, a long-term care pharmacy.

Edited by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

Reviewed by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

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