Novolog slow to take effect

I recently took a break from novolog as I was given a box of humalog to trial which I did. Yesterday my humalog ran out so I switched back to novo but for some reason im finding it’s taking an awfully long time to take effect.

Yesterday night I injected about 10 units for dinner. My sugar didn’t decline until about 1.5 h later . I must also say I had some soup to drink during the 20 minute prebolus period so that may have counteracted the decline a bit but wasn’t expecting it to take so long.

This morning I also bolus and my sugar didn’t drop after the 20 min mark. Still standing steady even after 30 mins.

Then I started thinking maybe it’s the site because I changed the site yesterday morning at the same time as the switch but if it was a site issue that doesn’t explain why the insulin did eventually take effect(the full force, I was nosediving).

Any reason this could be?

If you had something fatty with both your meals, it can cause insulin resistance.

It can be a site issue. If it doesn’t absorb well, but it does eventually work that definitely can be a site absorption issue. Usually if there isn’t an apparent reason, but my blood sugars are trending higher, staying higher longer, I will change my site and it has gone away. Insulin, especially higher doses of insulin can cause tunneling and just end up mostly sitting there, maybe absorbing over time.

1 Like

Not a fatty meal but I waited 1.5 hours for my sugar to come down before I started eating so the meal factor is not a contributing factor. The soup I had during prebolus had a bit of carbs but wasn’t fatty either.

I did change the site today to see whether it’s any better. Just found it weird not impacting my sugars after injection. At that point I was contemplating on whether I should do a manual bolus but worried if I did and the previous insulin started to take effect I’ll be in a bad place. It’s a difficult decision.

It could be absorption issues as you say, my sugar was running higher than normal overnight even after I did a few correction boluses during the night and a temp basal increase. It was like water.

What’s the best way to inject. 50% via pump and 50% manual on a different site?

I almost always do a manual injection when I change a site because of it not working well. But it is a guess about how much you need. It’s a judgement call and depends how bad your absorption issue is etc,

Tunneling seems to be an issue for some more than others but is more likely to occur with higher dosing. I get leery at anything over about 3-5 units? If I need over that I either extend part of the dose or give some 15-30 minutes apart. If I am having that high carb of a meal I have found it beneficial to split up my dosing anyways. Some of those carbs just like to hit later on me.

The overnight higher levels is usually a tell that it’s not a great site, unless you’re sick or have an infection. I bet it’s a site issue.


That is about the same rate that Novolog works for me. It will work faster I think when you are walking or the bg is low. I told my endo about this and he asked if I had gastropareses? I have even done a 45 min pre- bolous. I only do that if my bg is pretty high. when having trouble lowering my bg. I wait 1 hr to 2 before I dose some more. Everyone is different.


Oh that’s sucks, such a long wait time, I feel for you! I was previously on novo before humalog and I see my Dexcom reading start to trend down at the 20 min mark so I definitely know 1.5 hours is way too long for me and it just isn’t working.

I changed my site this morning and just bolused for lunch, will see whether it is a site issue. The other variable here is because it’s a new site it may take some more insulin to work - can’t really win! Haha

I have found that I have had several vials of humalog that were bad. I had tried manual injections to take the pump out of the question and after hours no response so I changed vials and bingo. three vials with the same lot number also ended up bad. I sent them back to the manufacture but have not heard anything back.

1 Like

I find novolog to be a tiny bit slower. But not that much difference.
It’s possible that you don’t respond as well to novolog, but I have weird swings from sites not absorbing, or eating more than I thought, or having more fat than I thought I was having.

I think you should eliminate the other variables before pinning it on the insulin.


Just an update, after changing the site this morning, my lunch bolus took effect at the 20 min mark so maybe it was bad site having absorption issues. I’ll keep an eye on this and see how I go tommorow.

I was too low to prebolus for dinner so can’t tell.


Hi… yeah, as far as I know, the timing of both is pretty similar… this sounds more like a site/sensitivity issue.

1 Like

I don’t know, my sugar overnight has been hard to bring down, it maybe due to hormones but coincidentally coincided with my switch back to novolog. Or maybe humalog worked better for me, I can’t quite put my finger on it yet but it just feels humalog is more predictable in what is to happen. Novolog has a bit of volatility

My Novolog activity lifetimes vary from 2 hours to 5 hours. I generally plan for a 5 hour activity period but those two hour periods happen from time to time, and my blood glucose goes quite low. I don’t vary my site much, and I have a repetitious lifestyle. I would love to know why the novolog action periods vary and if there’s anything that would tip off those variations.

I used the same amount of Humalog until I turned 60. Then it started working much slower and I needed much more. Seems to be a problem with getting older. (Also, my family has a history of Type 2 from before they knew how to treat it, but I got Type 1 in my 30s.) So, after 60, my body still didn’t produce any insulin (C-peptide 0.0) but I had insulin resistance, and my MDI worked very slowly. Now I take metformin to make my injections work. The insulin resistance is gone, but Humalog still works much slower than it did before I turned 60. My endocrinologist says he would love to give me Fiasp or Lyumjev, but they’re not available here. I understand inhaled insulin is even faster (but very expensive) and that is also not available here.
“Getting old is no fun, but it beats the alternative.”

Unless you’re hooked up to a continuous system that measures actual insulin concentrations in the blood, you can’t know the actual duration of insulin action. We can, however, observe glucose levels and draw inferences. But that indirect method can confuse.

If you check the package insert of any formulation of insulin, it will list the duration of insulin action. This duration is a composite of all the subjects tested so that it includes person to person variation. We should trust this number as a good one to use for treatment. It will not be far off from actual.

What does change in each of our bodies is our insulin sensitivity, both the action of external insulin absorbing into the tissue into which it is injected and the overall effect of cellular resistance to absorbing insulin and enabling insulin metabolism.

What I’m trying to say is that it is not the variation of insulin action that you observe but your body’s changing sensitivity to insulin that is responsible.

Diabetes is a dynamic system and insulin sensitivity is not a static (or even slowly changing) factor. Insulin sensitivity is influenced by many factors, including the qualities of the food we eat, our exercise status, how well we sleep, and the amount of chronic stress we may be under.

1 Like

To @Terry4 point… here’s the product packaging data for some rapid-acting insulins.

Here’s the complete post. Know Thy Insulins (

This 2014 article published in the Journal of Diabetes Science and Technology written by John Walsh and colleagues makes a pointed distinction between the terms, “duration of insulin action (DIA)” and “insulin action time (IAT).”

I realize that the original poster asked this question in the context of MDI usage but thought many insulin pump users might find this info useful.

The insulin duration times in your table, @Steve_Mann, look more like IAT times rather than DIA times.

It’s taken me some time to understand his point. He contends that DIA is longer than and completely contains IAT. The reason for this is due to the suppression of basal delivery in the test that measures IAT. The DIA time is measured with the usual basal background insulin. Here are two graphs from the study.

Why does this distinction matter? If we, as pump users, input the shorter IAT instead of DIA into the pumps settings then we take on additional risks of hypos due to insulin stacking.

Sorry for the detour into the weeds but I think many pump users set their pump DIA too short and then compensate with other pump settings. This distorts things and makes troubleshooting confusing.

The developers of the Loop DIY algorithm allow choices of various insulin models. The “Walsh” model enables choosing whatever DIA you fancy and that affects how Loop calculates its insulin delivery. (The Loop graph below shows the Walsh Model at a 6-hour DIA. This model, when chosen, permits any time to be selected.) The “Rapid-Acting – Adults” model fixes the DIA at 6 hours and uses an exponential curve to calculate insulin on board in its algorithm. I use this model.

Here’s an explanation from LoopDocs.

Insulin Model

There are four insulin models to choose from; Walsh, Rapid-Acting Adults, Rapid-Acting Children, and Fiasp. If you want to read the nitty-gritty discussion that went into the development of the Rapid-Acting and Fiasp curves (collectively called “exponential insulin models”), you can see that in GitHub here.

We highly recommend selecting one of the exponential insulin models (in other words, not the Walsh model).

A common new Loop user error is to select Walsh model in order to easily shorten their insulin duration (DIA) to one like they used prior to Looping. This almost invariably leads to insulin stacking. If you would like to read more about why the duration of insulin action is important in Loop vs how you’ve traditionally used it, please click here to read a blog post about the subject. In summary, choosing Walsh curve just to shorten your DIA will lead to insulin stacking and less than desired bolusing recommendations.

You can click on each model and see what each model’s insulin activity curve looks like, active one selected in blue.

The differences between the three exponential models (two Rapid-Acting and Fiasp) models has to do with the timing of the peak insulin activity timing. Not surprising, since Fiasp is marketed as the “faster acting” insulin. Currently all the exponential models are defaulted to an insulin duration of 6 hours, but the peak activity of the curves differs:

  • Rapid-acting adult curve peaks at 75 minutes
  • Rapid-acting child curve peaks at 65 minutes
  • Fiasp peaks curve peaks at 55 minutes

The key takeaway here is that setting a reasonable DIA time in your pump does matter. I can remember when I used an “aggressively short” DIA, like three hours and every once in a while getting hit with an unexpected severe hypo that in retrospect could only be attributed by that seemingly innocent “insulin tail” where I had thought that it was not consequential.

As more of us move into automated insulin dosing systems, we should not fall into the trap of carrying over a too-short DIA that may have appeared to work for us with a non-automated pump.