Handling & safety guide · chapter 07

Injection basics

Subcutaneous technique in eight illustrated steps: sites and rotation, needle length, single-use needles, and how pens differ from syringes.

General information, not medical advice. Approved drugs: follow your prescriber and the product's instructions for use.

This page describes a subcutaneous injection: into the layer of fat just under the skin. That is the route used by the approved peptide products cited in this guide [1][2][3]. It does not cover injections into muscle, veins, joints or anywhere else, and none of those should be attempted from a web page.

If you have a prescribed product, a nurse or pharmacist can watch you do your first injection. Ask. The instructions for use that come with an approved product say the same: have a healthcare provider show you [1].

Where: sites and rotation

Approved labels and patient guidance name the same three areas [1][2][4]:

  • Abdomen (belly): below the ribs and above the hip bones, at least 5 cm (2 inches) away from the navel.
  • Thigh: the front and outer part of the upper thigh.
  • Upper arm: the back or side of the upper arm, at least 7.5 cm (3 inches) below the shoulder and above the elbow. This area is hard to reach properly on yourself; labels describe it as a site for another person to inject [1].

Some products name one area only. Tesamorelin, for example, is labelled for the abdomen [3]. Use the sites your product's label lists.

Rotate every time. Use a new spot for each injection, at least 2.5 cm (1 inch) from the last one, and work around the area in a pattern instead of returning to a favourite spot [2][4]. Injecting the same spot repeatedly causes lumps, dents and thickened skin, and medicine injected into those areas is absorbed unpredictably [1][5].

Do not inject into skin that is tender, bruised, red, scaly, hard, scarred or damaged, or into an area that already has lumps or pits [1][3][4].

Needle length and gauge

  • Human skin at the usual injection sites is only about 2 mm thick, and that changes little with body size. The fat layer beneath it averages roughly 10 to 15 mm at these sites but varies a lot with sex and body size [6].
  • So a short needle is enough to get through the skin. Expert recommendations for insulin injection, the best-studied self-injection there is, make the shortest needles (4 mm on pens, 6 mm on syringes) the first choice for every adult, because they reach the fat reliably and are less likely to hit muscle [5].
  • Longer needles (8 mm, 12.7 mm) raise the chance of injecting into muscle, especially in the thigh and arm and in lean people. An injection into muscle hurts more and is absorbed at a different speed [5][6].
  • Gauge is thickness: the higher the number, the thinner the needle. Insulin-type syringes are typically 29 to 31 gauge.
  • A generic description of what is commonly used for small-volume subcutaneous injections: an insulin syringe, 0.3 to 1 mL, with a fixed 29–31 gauge needle 6 to 8 mm long.

One needle, one syringe, one time

  • Every injection uses a new, sterile needle and syringe. A used needle is no longer sterile and can block [1][7].
  • Never share needles, syringes, pens or vials with anyone. Changing the needle does not make a shared pen or syringe safe; blood-borne infections spread this way [1][7][8].
  • Never recap a used needle. Recapping is how people stab themselves [1]. It goes straight into a sharps container (see disposal).

The steps

Step 1 — Wash your hands, set out supplies, check the medicine

Wash your hands with soap and water [1][4]. On a clean surface set out the vial or pen, one new syringe (if using a vial), two alcohol swabs, a piece of clean gauze or cotton, and the sharps container. Check the label, the expiry or discard date, and the liquid against the warning signs checklist [1][9].

Ready to injectA clean tabletop with a labelled vial of clear liquid, one wrapped insulin-type syringe, two wrapped alcohol swabs, a square of gauze and an open sharps container. A pair of just-washed hands rests at the edge of the frame, with a small water-drop icon to show they are clean.
Step 1 Ready to inject

Step 2 — Choose today's site

Pick a spot in one of the areas above that is not the spot you used last time and has no bruise, lump or broken skin. Keeping a simple record (date and site) makes rotation reliable.

Site map and rotationA simple front-view outline of an adult body, gender-neutral, with three shaded zones: the abdomen (with a clear unshaded circle around the navel), the front-outer thighs, and the backs of the upper arms (shown in a small rear-view inset). Inside the abdomen zone, a ring of numbered dots 1 to 8 shows a rotation pattern moving around the navel.12345678back view
Step 2 Site map and rotation

Step 3 — Clean the skin and let it dry

Wipe the spot with an alcohol swab, moving outward in a circle, and let it air dry completely [4]. World Health Organization guidance treats washing with soap and water as sufficient skin preparation for injections under the skin [10]; product instructions usually ask for an alcohol swab as well. If the area is sweaty or dirty, wash it with soap and water first.

Clean the skinClose-up of a patch of abdomen skin. A hand wipes an alcohol swab in a spiral from the centre outward, shown with a spiral arrow. Small evaporation lines indicate the skin drying before anything else happens.
Step 3 Clean the skin

Step 4 — Swab the stopper and draw the dose

(Vial and syringe only. For a pen, attach a new pen needle or uncap the device as its instructions say.) Wipe the vial's rubber stopper with the second swab and let it dry [1][9]. Pull the plunger back to your dose mark to draw in air, push the needle through the stopper, and inject the air. Turn the vial upside down, keep the needle tip in the liquid, and draw slightly past your mark. Tap the barrel so bubbles rise, push them back into the vial, and stop exactly on your mark [1][9]. Read the syringe at eye level. The number you need comes from the mixing math page, worked out in advance.

Draw the doseA vial held upside down with a syringe drawing liquid from it. An enlarged circle shows the syringe barrel: the top edge of the plunger tip sits exactly on a tick mark, with a small bubble near the needle end and a finger flicking the barrel to move it upward. No numbers on the scale.
Step 4 Draw the dose

Step 5 — Insert the needle

With your free hand, gently pinch up about 2.5 cm (1 inch) of skin and fat, not muscle. Insert the needle in one quick, smooth motion: straight in (90 degrees) if there is a good fold of fat, or at 45 degrees if you are lean or the needle is longer [4]. With the shortest needles a pinch may not be needed; an approved product's instructions or your provider will say [1].

Angle and depthA cross-section of tissue in three flat colour bands labelled skin, fat and muscle. Two needles are shown side by side entering a gently pinched fold: one at 90 degrees and one at 45 degrees, both with their tips ending in the fat layer and well short of the muscle. Small angle arcs mark "90°" and "45°".skinfatmuscle90°45°
Step 5 Angle and depth

Step 6 — Push the plunger slowly, then wait

Release the pinch if your instructions say to [4]. Press the plunger slowly and steadily all the way down. Keep the needle in place for at least 5 seconds (some pens specify longer) so the full dose stays in [1].

Inject and holdA syringe in place in the abdomen with the thumb pressing the plunger fully down. A small counter beside it shows "1 · 2 · 3 · 4 · 5" to indicate the wait before removal.1 · 2 · 3 · 4 · 5
Step 6 Inject and hold

Step 7 — Withdraw, press, do not rub

Pull the needle straight out at the same angle it went in. If there is a drop of blood, press gently with clean gauze for a few seconds. Do not rub the area [1][4].

Press, don't rubA fingertip holds a small square of gauze flat and still against the injection spot. A small crossed-out inset shows a hand rubbing the skin in circles.
Step 7 Press, don't rub

Step 8 — Straight into the sharps container

Without recapping, bending or breaking the needle, drop the whole syringe (or pen needle) into the sharps container immediately [1][11]. Put the vial back in the fridge if it is a multi-dose vial within its dates; a single-dose vial is discarded after one use even if liquid is left [1]. Wash your hands, and note the date and site.

Sharps container, no recappingA hand drops an uncapped used syringe, needle first, through the opening of a sturdy sharps container marked with a generic hazard symbol. The loose needle cap lies on the table with a crossed-out arrow showing it is not put back on.
Step 8 Sharps container, no recapping

Pens versus syringes

Pen or autoinjector Vial and syringe
Who measures the dose The device. The manufacturer fixes the concentration; you press a button or dial a number. You do. The dose depends on your arithmetic and your eyesight.
Steps Few. Single-dose autoinjectors hide the needle and inject at a set depth. Many: swab, draw air, draw dose, clear bubbles, read the scale.
Accuracy at small doses Pen injectors were more accurate than syringes at small volumes in laboratory testing [12]. Less accurate, with a tendency to overdose at very small volumes [12].
Needles Multi-dose pens need a new pen needle for every injection. Single-dose pens are thrown away whole. A new syringe and needle every time.
Sharing Never, even with a new needle [8]. Never.
In-use limits Set by the label (for example, one semaglutide pen is discarded 56 days after first use) [13]. Set by the label, or by the limits in storage.
Main risks Using the device wrongly; injecting before reading its instructions. Measuring errors between mg, mL and units [14]; contamination from repeated handling.

Neither is "safer" in itself. A pen removes arithmetic and several chances for contamination. A vial and syringe put both in your hands.

Sources

Checked 13 November 2026.

  1. Tirzepatide (Zepbound) single-dose vial, Instructions for Use (revised April 2026). (link not shown: non-primary host)
  2. Semaglutide (Wegovy), US prescribing information, DailyMed. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=ee06186f-2aa3-4990-a760-757579d8f77b
  3. Tesamorelin for injection (Egrifta WR), US prescribing information and instructions for use, DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=839334d3-8c1d-4c26-9036-2ab524a6ea75
  4. MedlinePlus Medical Encyclopedia. "Subcutaneous (SQ) injections." https://medlineplus.gov/ency/patientinstructions/000430.htm
  5. Frid AH, Kreugel G, Grassi G, et al. "New Insulin Delivery Recommendations." Mayo Clinic Proceedings. 2016;91(9):1231–1255. https://doi.org/10.1016/j.mayocp.2016.06.010
  6. Gibney MA, Arce CH, Byron KJ, Hirsch LJ. "Skin and subcutaneous adipose layer thickness in adults with diabetes at sites used for insulin injections: implications for needle length recommendations." Current Medical Research and Opinion. 2010;26(6):1519–1530. https://doi.org/10.1185/03007995.2010.481203
  7. U.S. Centers for Disease Control and Prevention. "Preventing Unsafe Injection Practices." https://www.cdc.gov/injection-safety/hcp/clinical-safety/index.html
  8. Tirzepatide injection (Zepbound), US prescribing information, DailyMed (section 5.10, never share a pen between patients). https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=487cd7e7-434c-4925-99fa-aa80b1cc776b&type=display
  9. MedlinePlus Medical Encyclopedia. "Drawing medicine out of a vial." https://medlineplus.gov/ency/patientinstructions/000530.htm
  10. World Health Organization. "WHO Best Practices for Injections and Related Procedures Toolkit" (2010), chapter 2, "Best practices for injection." https://www.ncbi.nlm.nih.gov/books/NBK138495/
  11. U.S. Food and Drug Administration. "Safely Using Sharps (Needles and Syringes) at Home, at Work and on Travel." https://www.fda.gov/medical-devices/consumer-products/safely-using-sharps-needles-and-syringes-home-work-and-travel
  12. Gnanalingham MG, Newland P, Smith CP. "Accuracy and reproducibility of low dose insulin administration using pen-injectors and syringes." Archives of Disease in Childhood. 1998;79(1):59–62. https://doi.org/10.1136/adc.79.1.59
  13. Semaglutide (Ozempic), US prescribing information. (link not shown: non-primary host)
  14. U.S. Food and Drug Administration. "FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products" (26 July 2024). https://www.fda.gov/drugs/human-drug-compounding/fda-alerts-health-care-providers-compounders-and-patients-dosing-errors-associated-compounded