Priming an insulin pen takes about 10 seconds and involves dialing 2 units, pointing the pen upward, and pressing the injection button until you see a drop of insulin at the needle tip. You need to do this before every injection, not just when you start a new pen. Skipping this step can mean air bubbles displace insulin inside the pen, leading to an inaccurate dose.
Why Priming Matters
Small air bubbles naturally collect inside an insulin pen cartridge over time, especially with temperature changes or when you attach a new needle. These bubbles take up space where insulin should be. If you inject without clearing them, you could get less insulin than your dial shows, because the air pushes through instead of medication. For someone relying on precise dosing to manage blood sugar, even a small shortfall can throw off glucose control for hours.
Priming also confirms that the needle is properly attached and that insulin can flow through it. A clogged or poorly seated needle won’t produce a visible drop, which tells you something needs to be fixed before you inject.
Step-by-Step Priming Process
These steps apply to virtually all disposable and reusable insulin pens, regardless of brand. The process is the same whether you’re using a rapid-acting or long-acting insulin.
- Attach a new needle. Remove the outer cap from the pen, screw on a fresh pen needle, and pull off both the outer and inner needle caps. Never reuse a needle from a previous injection, as this increases the chance of clogs and air entering the cartridge.
- Dial to 2 units. Turn the dosage knob until the display reads 2. This is the standard priming dose recommended across pen brands.
- Point the pen straight up. Hold it with the needle facing the ceiling. Tap the cartridge gently a few times with your finger. This encourages any air bubbles to rise to the top, closer to the needle, where they can be expelled.
- Press the injection button. Push the button (or plunger) all the way in with your thumb while keeping the pen pointed up. You should see at least one drop of insulin appear at the needle tip.
- Check for the drop. A visible bead of insulin at the tip of the needle is your confirmation that the pen is working correctly and air has been cleared. If you don’t see a drop, repeat the process: dial 2 units again, point up, and press. A brand-new cartridge may need several rounds of priming before insulin appears.
Once you see that drop, you’re ready to dial your actual prescribed dose and inject normally.
What to Do If No Drop Appears
If you’ve primed three or four times and still don’t see insulin at the needle tip, start by removing the needle and attaching a new one. The needle itself may be blocked. Try priming again with the fresh needle.
If a new needle doesn’t solve it, check the cartridge. Hold the pen up to the light and look at the insulin window. If the cartridge is empty or nearly empty, that’s your answer. Some pens make it hard to tell how much is left, so rotating the pen slowly while looking at the window can help. If there’s insulin visible but it still won’t prime, the pen’s internal mechanism may be damaged. Replace the pen entirely rather than injecting with one you can’t confirm is working.
Common Mistakes That Affect Priming
The most frequent error is forgetting to point the pen upward. Air rises, so if you hold the pen sideways or pointed down, bubbles stay trapped in the middle of the cartridge instead of moving toward the needle where they can be expelled. You’ll see insulin come out and assume the pen is primed, but air remains inside and will affect a later dose.
Another common mistake is skipping the prime when you’re in a hurry or injecting in public. It’s tempting to assume the pen is fine because it worked last time, but air enters the cartridge every time you remove and attach a needle. Even small temperature shifts between injections can cause dissolved gases to form new bubbles. Priming every single time is the only way to ensure dose accuracy.
Some people also prime with more than 2 units, thinking extra priming is safer. While it won’t hurt anything mechanically, it does waste insulin. Over the life of a pen, those extra units add up and can mean your cartridge runs out sooner than expected. Two units is sufficient to clear the needle and confirm flow.
Priming a New Pen vs. a Pen in Use
When you start a brand-new pen or insert a fresh cartridge into a reusable pen, expect to prime more than once. New cartridges often have a larger air pocket at the top, and the insulin needs to fill the needle mechanism for the first time. Three to five rounds of 2-unit primes is normal before you see that first drop.
For a pen you’re already using (same cartridge, new needle for today’s injection), one prime of 2 units is usually enough. If a drop appears on the first try, you’re good to go. The cartridge already has insulin seated in the mechanism, so you’re mainly clearing the new needle and any small air bubble that entered when you attached it.