Needle & Syringe Guide

Understanding Needle Gauge

Needle gauge refers to the diameter (thickness) of the needle. The gauge system is counterintuitive: higher gauge numbers mean thinner needles. A 31-gauge needle is thinner than a 25-gauge needle. For subcutaneous peptide injections, thinner needles are preferred because they cause less discomfort.

Common Gauges for Peptide Use

• 29-31 gauge: Standard for subcutaneous injection. These are the same needles used for insulin. They are thin enough to minimize pain while still allowing peptide solutions to flow through easily. Most peptide users will use needles in this range.
• 27 gauge: Slightly thicker. Sometimes used for drawing from vials (because thinner needles draw more slowly) or for slightly more viscous solutions.
• 25 gauge: Used primarily for intramuscular injections or for drawing from vials with thicker stoppers. Too thick for comfortable subcutaneous injection in most cases.
• 22-23 gauge: Used for drawing from vials when a separate injection needle will be used. Never use these gauges for subcutaneous injection.

Needle Length

Needle length determines how deep the needle penetrates. The correct length depends on the type of injection and your body composition.

Subcutaneous Injections

SubQ injections target the fat layer just beneath the skin. Appropriate needle lengths are:

• 5/16 inch (8 mm): The most common length for subQ injections. Works well for most body types.
• 1/2 inch (12.7 mm): Suitable for individuals with more subcutaneous fat. When using this length, inject at a 45-degree angle to avoid reaching muscle tissue.

Intramuscular Injections

IM injections (such as testosterone) target muscle tissue and require longer needles:

• 1 inch (25 mm): Suitable for deltoid (shoulder) injections in individuals with moderate body composition.
• 1 to 1.5 inch (25-38 mm): Standard for gluteal (buttock) or vastus lateralis (outer thigh) injections. The exact length depends on body composition — your provider will advise.

Syringe Types and Volumes

Insulin Syringes

Insulin syringes are the most commonly used for peptide injections. They come with the needle permanently attached and are marked in "units" rather than milliliters.

• 0.3 mL (30-unit) syringe: Best for small doses. The markings are spaced farther apart, making it easier to measure precise small amounts. Each small line typically represents 0.5 units.
• 0.5 mL (50-unit) syringe: A good all-purpose size. Each small line represents 1 unit.
• 1 mL (100-unit) syringe: Best for larger doses. Each small line represents 2 units. Less precise for very small doses.

Key conversion: On an insulin syringe, 100 units = 1 mL. Therefore, 10 units = 0.1 mL, and 1 unit = 0.01 mL.

Luer-Lock Syringes

These have a detachable needle that screws on. They are useful when you want to use one needle to draw from a vial and a separate, fresh needle for injection. Common for intramuscular injections like testosterone. They come in 1 mL, 3 mL, 5 mL, and larger sizes. For peptide protocols, 1 mL or 3 mL is standard.

Reading Syringe Markings

Misreading syringe markings is one of the most common dosing errors. Take time to familiarize yourself with your specific syringe before drawing your first dose.

• Identify the unit scale: Look at the numbers printed on the barrel. Note whether the markings go to 30, 50, or 100.
• Count the lines between numbers: On a 100-unit syringe, each line between 0 and 10 represents 2 units. On a 50-unit syringe, each line typically represents 1 unit.
• Read at eye level: Hold the syringe at eye level and read the measurement at the top of the plunger's rubber stopper (the flat edge closest to the needle).

Drawing From a Vial

1. Clean the vial stopper with an alcohol swab and let it dry.
2. Pull back the plunger to draw air equal to the volume of liquid you plan to withdraw.
3. Insert the needle through the stopper and inject the air into the vial. This equalizes pressure and makes drawing easier.
4. Invert the vial so the needle tip is submerged in the liquid.
5. Pull back the plunger slowly to your desired dose marking.
6. Tap the syringe barrel gently to move air bubbles toward the needle, then push the plunger slightly to expel them.
7. Confirm the dose, withdraw the needle from the vial, and proceed to injection.

Pro Tips

• Use a separate drawing needle: If using a Luer-lock syringe, draw your dose with a larger gauge (22-25G) needle, then swap to a thinner gauge (27-31G) for injection. The drawing needle penetrates the stopper more easily and preserves the sharpness of your injection needle.
• Store supplies properly: Keep unused syringes and needles in their sealed packaging in a clean, dry location.
• Never bend or recap needles: This is the leading cause of accidental needlestick injuries. Place used sharps directly into a sharps container.