Insulin seeming to do nothing
Usually the site, the insulin, the kit or an illness rather than the dose. A checklist to run in order, and why repeating doses and waiting is the wrong move.
When insulin seems to be doing nothing, the instinct is to conclude something is wrong with you. Usually something much more boring is wrong with the delivery: the site, the insulin itself, the kit, or an illness working against it. This is a checklist rather than a mystery, and running it in order saves a lot of frustration.
- The site is the most common culprit. An overused or lumpy area absorbs slowly and unpredictably however good the dose was.
- The insulin itself can be the problem: heat, freezing or age all damage it, and damaged insulin looks exactly like a dosing failure.
- The kit: a bent cannula, a leak, an air bubble or a pump that has stopped means insulin never arrived at all.
- Illness and infection raise your needs sharply, so the usual amounts genuinely stop being enough for a while.
- If glucose stays high and will not come down, check for ketones rather than repeating doses and waiting.
- Watch for the other direction afterwards: once a blocked site or a stopped pump is fixed, insulin that has been stacking up can all work at once, and a hypo (a low below 4 mmol/L where you feel shaky, sweaty or confused and need fast sugar) can follow hours later.
Four things to rule out before blaming the dose
Start with the site, because it is both the most likely and the easiest to change. Skin that has been used a lot builds up firm patches under the surface, and insulin delivered into one of those absorbs slowly and erratically. The area can look completely normal and still behave badly, so it is worth feeling for lumps rather than looking for them. Moving to fresh skin is a change you can make yourself and often resolves the whole thing.
Then the insulin. It is a protein and it is fragile: left in a hot car, frozen at the back of a fridge, or simply in use for longer than it should be, it loses potency. Cloudiness or clumps in something that should be clear is a giveaway, but plenty of damaged insulin looks perfectly fine. If everything else checks out, trying a fresh vial or pen is a reasonable next step.
Then the kit, which matters most on a pump. A cannula can bend on insertion and deliver into almost nothing, a set can leak so that the insulin ends up on your skin rather than under it, and a pump can stop or fail to resume after being suspended. If you inject, an air bubble or a needle that has come out early does the same job.
Then illness. An infection or a virus raises insulin needs substantially, and it can start before you feel obviously unwell. If your usual amounts have stopped working across the board rather than at one site or one meal, something systemic is often behind it.
Why repeating doses and waiting is the wrong response
The dangerous version of this is a pump or site failure, because insulin has effectively stopped rather than merely been weak. On a pump there is no long-acting insulin behind it, so the gap becomes a real absence quickly, and glucose plus ketones climb together. That is the road to DKA, and it can happen in hours.
Which is why the response to “insulin is doing nothing” should never be to give more through the same route and wait to see. If the route is the problem, more insulin down the same route does nothing at all except waste the time in which the situation gets worse. Changing the site or the set, and checking ketones, comes first.
Ketones are the thing that separates a frustrating afternoon from an urgent one. A high that will not come down with ketones present is a different situation from the same number without them, and your team will have given you a plan for it. That plan is worth knowing before you need it rather than looking for at the time.
What it looks like when nothing is broken
Sometimes the delivery is fine and your needs have genuinely changed. That looks different from a failure: it is gradual rather than sudden, it applies across meals and days rather than at one site, and it usually has a reason behind it, such as growth, a change in activity, weight change, a new medication, or a stretch of stress.
The clue is the shape. A site or kit problem tends to appear abruptly and resolve abruptly when you change it. A genuine change in needs drifts over days or weeks and does not care which site you use. Noticing which of those you are looking at is most of what turns an appointment from vague to useful.
Either way the adjustment belongs with your team. What is yours is the observation: what you tried, in what order, and what happened, which is a far better thing to bring than a fortnight of unexplained highs.
What makes this more likely
Pumps concentrate the risk into one site at a time, which is why a set problem shows up faster and harder than an injection problem does. Heat is the most underestimated factor: a summer car, a windowsill, a poolside bag. And a vial in use for weeks past its in-use life is a genuinely common and entirely invisible cause of insulin that has quietly stopped doing much.
Which one is it?
Examples, not instructions or doses.
Highs all day that nothing touches, then you change the site and within hours everything behaves. That was absorption, and the doses were fine all along.
Everything worked until the insulin spent a day in the car. A fresh pen behaves normally, which is the answer and also a reminder about where it travels.
Nothing broke, but over a few weeks the usual amounts do a bit less across every meal and every site. That shape is a change in needs, not a failure, and it is a conversation for your team.
When it's urgent
Insulin that is not getting in leads to high glucose and ketones, and that can become DKA within hours, especially on a pump where there is no long-acting insulin behind it. If your glucose is high and not coming down, check for ketones rather than repeating doses and waiting, and follow the plan your team gave you. If you are being sick and cannot keep fluids down, have stomach pain, are breathing fast or deeply, or feel very unwell, contact your diabetes team or call NHS 111. If you are drowsy, confused or breathing very fast, call 999.