How to Inject a GLP-1: The Step-by-Step Technique Guide for Pens, Vials, and Compounded Syringes

Most GLP-1 patients never get a real hands-on injection lesson. You get the pen, a quick clinic demonstration if you're lucky, a one-page leaflet, and a link to the manufacturer's YouTube video. This is the written reference for every common GLP-1 delivery format: pre-filled single-use pens, multi-dose pens, multi-dose vials with regular syringes, and compounded vials with U-100 insulin syringes. Click-by-click, site-by-site, and the troubleshooting list for what to do when something goes wrong.

The three things that are the same for every GLP-1 injection

Regardless of which device you use, three rules apply universally to all subcutaneous GLP-1 injections^[5][6]:

1. Subcutaneous, not intramuscular. GLP-1s are designed to be absorbed from the fat layer just under the skin, not from muscle. Hitting muscle changes the absorption profile and can hurt more.
2. Rotate sites. Repeatedly injecting the same spot causes lipohypertrophy — fatty lumps under the skin that look normal but absorb the drug erratically (often 25-50% less than fresh tissue).
3. Clean technique, but not sterile theater. Wash your hands. Wipe the skin with alcohol and let it dry (alcohol on wet skin stings). Use a fresh needle every time. You do not need gloves or a mask.

Where to inject (the FDA-approved sites)

The Wegovy^[1], Ozempic^[2], Zepbound^[3], and Mounjaro^[4] labels all approve the same three injection sites:

• Abdomen — anywhere on the front of the abdomen, at least 2 inches (5 cm) away from the navel. This is the most popular site because there's typically the most subcutaneous fat and the easiest visualization.
• Front of the thigh — the upper outer quadrant of the front of the thigh. Avoid the inner thigh.
• Upper arm — the back of the upper arm, in the fatty area between the shoulder and elbow. This is the one site most patients can't comfortably reach themselves and may need help with.

See our where-to-inject anatomy guide for site diagrams and the rotation pattern that minimizes lipohypertrophy.

Pre-filled single-use pens (Wegovy and Zepbound)

Wegovy and Zepbound ship as single-use auto-injector pens. Each pen contains exactly one weekly dose. You twist off the cap, press the pen against the skin, and a spring delivers the full dose. There is no dial, no air bubble check, and no partial dose. The trade-off for the simplicity is that each dose costs more to manufacture, which is part of why brand-name Wegovy and Zepbound are expensive.

Step-by-step from the FDA labels^[1][3]:

1. Take the pen out of the refrigerator 15-30 minutes before injecting. Cold injections sting more.
2. Inspect the pen window. The liquid should be clear and colorless. If it's cloudy, discolored, or has particles, do not use the pen — call the pharmacy.
3. Wash your hands.
4. Choose your injection site (abdomen, thigh, or upper arm) and clean with alcohol. Let the alcohol dry completely.
5. Pull off the pen cap. Do not put the cap back on — for Wegovy and Zepbound, removing the cap arms the device.
6. Press the pen flat against the skin. You should feel firm contact, not just a touch.
7. Press and hold the injection button. You will hear a first click as the needle enters and the dose starts. Hold the pen firmly against the skin and wait for the second click and for the yellow indicator to stop moving — this is the drug being delivered.
8. The Wegovy label specifies hold for 5-10 seconds after the click stops to make sure the full dose is delivered. The Zepbound label specifies hold for 10 seconds. Lifting the pen too early is the most common cause of partial doses.
9. Lift the pen straight off the skin.
10. Dispose of the entire pen in an FDA-cleared sharps container. Do not recap.

Multi-dose pens (Ozempic and Mounjaro)

Ozempic comes in a multi-dose pen that delivers 4 doses (0.25 mg starter pen) or 4 weekly doses (0.5 mg, 1 mg, or 2 mg maintenance pen). Mounjaro comes as four single-use pens per carton, similar to Zepbound. The Ozempic multi-dose technique is the one that requires the most patient skill^[2]:

1. Wash hands and inspect the pen as above.
2. Attach a new needle. Twist on a fresh needle (typically a NovoFine 32G 4mm or similar), pull off the outer cap, and set the inner cap aside.
3. Flow check (every new pen, every new needle). Turn the dose selector to the flow check symbol (Ozempic shows two vertical dots). Hold the pen with the needle pointing up. Press the dose button. A drop of liquid should appear at the tip of the needle. If no drop appears after 6 attempts, change the needle. If still no drop, do not use the pen — call the manufacturer.
4. Turn the dose selector to your prescribed dose. The dial shows your dose number; turning the dial advances a fixed mechanical stop.
5. Choose and clean your injection site.
6. Insert the needle straight in (90° to the skin) at full depth. With a 4 mm needle there is no need to pinch the skin in most adults.
7. Press and hold the dose button until the dose counter returns to 0. Then continue holding the needle in place for at least 6 seconds (Ozempic label specifies 6 seconds — you can count slowly to 10 to be safe). This is critical because the drug needs time to spread into the tissue rather than back-flow up the needle track.
8. Pull the needle straight out.
9. Replace the inner needle cap (use the table-edge or one-handed scoop technique — never the two-hand recap-from-the-fingertip method which causes most needle stick injuries), unscrew the needle, and dispose in a sharps container.
10. Replace the pen cap and store the pen back in the refrigerator (or at room temperature for the labeled duration if you're traveling — see our storage and shelf life guide).

Multi-dose vials with a regular syringe

If your prescription is dispensed as a multi-dose vial (less common for brand-name GLP-1s but common for compounded semaglutide and tirzepatide), you draw up each dose yourself. The technique is the same as drawing up insulin from a vial:

1. Wash hands and inspect the vial. Liquid should be clear and colorless.
2. Wipe the rubber stopper of the vial with alcohol and let it dry.
3. Draw air into the syringe equal to your dose volume. Inject the air into the vial (vial up, syringe needle through the stopper). This equalizes pressure.
4. Invert the vial and draw your dose into the syringe. Tap out air bubbles by flicking the syringe with the needle pointing up, then push them back into the vial.
5. Pull the needle out of the vial. Re-verify the dose volume against your prescription.
6. Inject as described in the “injecting” section below.
7. Recap the vial, return to the refrigerator, and dispose of the syringe in a sharps container.

Compounded vials with a U-100 insulin syringe

Compounded semaglutide and tirzepatide are typically dispensed as multi-dose vials with U-100 insulin syringes. The wrinkle is that the syringe is graduated in insulin units, not milliliters or milligrams, so you need to know your concentration to convert your prescribed milligrams to syringe units. Use our GLP-1 unit converter for the math at any concentration.

Once you know how many units to draw, the technique is the same as drawing from a regular vial except that the insulin syringe is much smaller (typically 0.3 mL or 0.5 mL total volume) and the needle is much shorter (5/16 inch or 8 mm). At these short needle lengths, a 90° straight-in injection at full depth is correct for almost every adult and pinching the skin is unnecessary.

The injection itself (any device)

1. Hold the device like a dart or a pen — whichever feels more stable to you.
2. For a 4-8 mm needle, insert straight in at 90° to the skin. For a longer needle (12 mm or more), pinch a fold of skin and inject at 45° into the fold to avoid hitting muscle.
3. Push the needle in completely in one smooth motion. Do not stab.
4. Press the plunger down slowly and steadily. Faster is more painful and increases backflow.
5. When the plunger is fully down, count to at least 10 before withdrawing the needle. This is the single most important step for getting the full dose into the tissue and not back out the needle track.
6. Pull the needle straight out. Do not rub the site (rubbing spreads the drug into a wider area and can affect absorption).
7. A small drop of blood is normal and means a tiny capillary was nicked. Press gently with a clean tissue for 30 seconds.

Common mistakes (and how to avoid them)

• Lifting the pen or needle too early. The single biggest cause of partial doses. Always count to 10.
• Injecting cold drug straight from the fridge. More painful and can sting for hours. Let the pen or vial warm to room temperature for 15-30 minutes first.
• Injecting through clothing. The label says don't. Cloth fibers can be carried into the tissue and you can't see whether the needle entered correctly.
• Injecting in the same spot repeatedly. Lipohypertrophy is the result; absorption becomes erratic and weight loss can plateau for non-pharmacologic reasons. Rotate sites every injection.
• Reusing needles. Needles are designed for single use. Reusing dulls the bevel, increases pain, and increases infection risk.
• Skipping the alcohol-dry step. Wet alcohol on the skin stings when the needle goes in. Wait 10-15 seconds for it to dry.
• Recapping needles two-handed. The most common needle stick injury in patients is from recapping with both hands. Use the one-handed scoop or the table-edge technique, or just drop the uncapped needle straight into the sharps container.

What a normal injection site reaction looks like

• Normal: a small red dot at the injection site that fades within a few hours, occasional pinpoint bruising, or a slightly warm spot that resolves overnight.
• Mild reaction (still normal): a 1-2 cm area of redness or itching at the site that resolves within 1-2 days. More common with the first few doses.
• Concerning: spreading redness larger than a quarter, pain that worsens after 24 hours, warmth that spreads, pus, fever, or red streaks moving away from the site. These can indicate cellulitis or an abscess and warrant a call to your prescriber within 24 hours.
• Lipohypertrophy: a soft, fatty lump under the skin where you inject repeatedly. Not painful, not inflamed, but the drug doesn't absorb properly through it. Stop injecting in that spot and rotate to a fresh area.

Troubleshooting checklist

• The needle bent or broke off. If you can see the needle, remove it with clean tweezers. If you can't see it, leave it alone, mark the spot with a pen, and go to urgent care or your primary care office for imaging and removal. Do not dig.
• I think I only got a partial dose. For single-use pens (Wegovy, Zepbound), do NOT take a second dose to make up. Continue with your normal weekly schedule on the next scheduled day. For multi-dose pens (Ozempic), check the dose counter — if it stopped before reaching 0, the manufacturer's recommendation is to call them before re-dosing. Do not just inject again unless your prescriber tells you to.
• I missed my weekly dose. For weekly injectable GLP-1s, the FDA labels say if it's within 5 days of the missed dose, take it as soon as you remember and continue your normal weekly schedule. If it's more than 5 days, skip the missed dose and take your next scheduled dose. Do not double up.
• I left the pen out of the refrigerator overnight. The Wegovy and Zepbound labels allow up to 28 days at temperatures up to 86°F (30°C) for an unopened pen, and Ozempic allows up to 56 days for the in-use pen. Within those windows, the pen is safe to use. See our storage guide for the full out-of-fridge tolerance for each drug.
• I accidentally injected into muscle. Most common if you're lean or used a long needle in the arm. Absorption may be a bit faster but you don't need to do anything. Rotate to a fattier site next time and consider a shorter needle.

What to bring to your prescriber visit if you're struggling

• The actual pen or vial (or a photo)
• A list of which sites you've been using
• Photos of any concerning skin reactions or lumps
• A note of how long you're holding the needle in place after pressing the button
• Your weight loss (or lack of it) timeline — sometimes a plateau is a technique problem rather than a drug problem

Bottom line

• Subcutaneous, not intramuscular. Rotate sites every injection. Use a fresh needle every time.
• Hold the device against the skin for the FDA-labeled dwell time after the click or after the plunger reaches 0 (5-10 seconds for Wegovy, 10 seconds for Zepbound, 6 seconds for Ozempic). This is the single most important technique step.
• Let the pen warm up out of the fridge before injecting, and let alcohol dry completely before the needle goes in.
• Compounded vials with insulin syringes — convert mg to units with the right concentration math. Use our unit converter tool.
• Spreading redness, pus, fever, or red streaks = call your prescriber. Normal pinpoint redness and bruising = no action needed.

Related research and tools

• Where to inject: site anatomy guide — site diagrams and the rotation pattern
• GLP-1 unit converter — mg to insulin syringe units math for compounded vials
• Compounded vial reconstitution guide — for lyophilized compounded vials that arrive as powder
• Storage and shelf life — fridge and out-of-fridge windows for every drug
• Wegovy pen vs compounded vial — practical differences
• GLP-1 drug interaction checker — search any medication for its interaction with your GLP-1

Important disclaimer. This article is educational and does not replace the demonstration and instructions you should receive from your prescriber or pharmacist. Always follow the actual product insert that ships with your medication, and contact your prescribing clinician with any questions specific to your situation.