T1D- Sudden & Dramatic decrease in Insulin Sensitivity

So, I’ve had this really sudden and dramatic decrease in my insulin sensitivity, and I can’t explain it or get it under control. Looking for help with both. I use Smart MDI (CGM + InPen), Tresiba, and now Humalog.

About 1 week ago, I switched to Humalog from Novolog due to insurance. The previous week and prior, my numbers were totally normal, all good. That morning after breakfast, I was high. Found it strange since I ate things I knew the carb count for, but whatever, it’s the betes, ■■■■ happens. But, as the day goes on, I can’t get my BG down despite how insulin I take. I took nearly 3x the amount I should for boluses/corrections and still couldn’t get it under 200. And basically ever since then, I’ve been increasing my basal/bolus/correction dosages, with no success. I thought after increasing my basal by 66% the last two days (mind you Tresiba changes take 2-3 days to make a difference in BG), and increasing my bolus 3x, and I got a solid 3 hrs in range that MAYBE just maybe, I had figured it out. NOPE.

Just before bed last night, I was 115, drank an exactly measured 1 cup of milk and bolused triple my normal amount for it. I rose to a whopping 355 before I woke up and caught it. Even if I hadn’t bolused for that milk, I shouldn’t have rose to 355.

Luckily, I know my correction ratio at that time is good because I dropped to a steady 85. However, then dawn phenomenon hit and I rose back up. At 85, I’d normally raise to a 145, but today it rose to 205, suggesting it was more than just dawn phenomenon.

I haven’t changed diet, no change in weight, no exercise change (I am pretty active in general tho), no hormones at play, no dehydration or lack of sleep or whatever else you can typically think of. I literally can’t find a single change in my life that could cause this.

Now, I will preface this with that I am someone who is constantly changing my doses… usually in very small amounts, but I’m always adjusting every 2-3 weeks. My endo isn’t quite sure why but thinks it might be a form of brittle diabetes. Anyone with that experience the same thing?

I’m honestly soo emotionally drained and tired of all of this. I haven’t been below 200 for more than a handful of hours this past week. I am putting in the work to analyze every aspect of my life and BGs, and increasing dosages as I should, but it is literally not making a single difference and I just feel like a complete failure at the moment. Just looking for any ideas/answers or honestly even just someone else who has dealt with this.

When that has happened to me I check all my infusion sites and then change the insulin vial. It has been very hot lately maybe the insulin was damaged. Also maybe humolog is thicker than .novolog. My rule of thumb is if stays over 200 after I correct 2 times or so and get only minimal improvement over 3 hrs and I analyze the usual suspects then I change the vial. I never used Inpen so I do not know how it works. I usually keep the old vial in fridge until I am sure it not the cause. It is frustrating. I know. Keep us posted. I have been on both Humolog and Novolog and I do not remember any great difference in the dosing.

1 Like

My vote would be: bad insulin. It’s rare, I know, but it happens.
I’m on a pump.
Once I’ve ruled out illness, stress, reacting to over treating a low, eating something I shouldn’t have (hello, potato chips) and a bad infusion site, what else is left?


I also got the forced instance switch a few weeks ago. My pharmacy called me, as a courtesy they said, to let me know that insurance denied my Novolog, I had to switch to the generic Admelog, and that my doctor had already signed off on the change. I was so angry, since I already have a known bad reaction to Humalog on my record. I guess they got confused by the different name (even though it’s her by the same exact company from the same exact production lines/supply as Humalog), or didn’t check my file. I went ahead and tried it, since I figured out some inflammation triggers since the last time I did. Maybe it wasn’t actually the insulin… But it was awful! I went from high 90’s% TIR to barely 40%. Like you, I was taking 3x the amount of insulin, but it was like bolusing water. I was still seeing insanely high numbers after even looking at a carb, followed by insane lows at the 8-9 hour mark. Rapid acting insulin isn’t supposed to last that long in the system! The good numbers only happened when transitioning from the high phase to the low phase.

The good news is that you don’t HAVE to take that insulin, it’s just what your insurance prefers because they get it cheaper. Call your doctor ASAP to report “failed therapy”. It’s all the reason insurance needs to grant a prior authorization for your preferred med. If it’s not working for you, it’s not working for you. If you can’t meet treatment goals with that insulin, then they particular therapy has failed. I tried the Admelog for 4 days (odd number for a pumper, but I went through my first cartridge of insulin in just over a day), called the Doctor to tell them “hell no”, and 2 days later I had a new, shiny prescription for Novolog.

I have a theory about Humalog I’ve been considering writing up, but go back and forth because I don’t see much talk about food sensitivities here. It could possibly explain your delayed reaction, too. Have you tested yourself for a food sensitivity to nightshades? Tomatoes, peppers, potatoes, etc… I’m not asking if you get sick when you eat them, but very specifically if you’ve ever eliminated them from your diet, and then challenged reintroducing them, such as trying AIP (AutoImmune Paleo/Protocol).

1 Like

If you aren’t changing the pen needles every time you use Tresiba, it could be that you aren’t getting insulin. I wasn’t changing the needles after almost every injection, and didn’t realize that I wasn’t getting enough insulin. With both Novolog and Tresiba changing the needles is mandatory.


The molecule structure of Novolog and Humalog are different. Its possible you have antibodies for humalog which are also now impacting the Tresiba.

Its a total guess but you may want to have an anti-insulin antibody test done. Tresiba/Humalog/Novolog are all analogs. You may want to try human insulin while you are figuring this out. I would get a box of afrezza and see what it does.


The modern pen needles are indeed way skinnier than the syringe needles you and I were using half a century ago. Even the big old needles would plug up if re-used, possibly hastened by the less pure composition of the insulin back then.

They do indeed plug up sometimes if being re-used and even more so if allowed to sit a whole day between uses.

“plugged needle” can also happen with a brand new needle and is something I can usually sense while depressing the pen button. But for sure the quality of the tactile/audible feedback from the pen button varies A LOT. The Humalog pens offer very little positive feedback, the Tresiba pens are much better.


I thnnk you should try pulling the insulin with a syringe to make sure you are getting the right dose. With a syringe you can visually see how much you are getting.

When I was using pens this happened a few times where the pens under delivered.

I suggest you try that and see if your sugars return to normal.
If it works, then look into what is wrong with the pens. A slight bend in the needle can cause this or even if you don’t inject at a perfect 90 degrees.

I think the insulin resistance is not likely to com on all of a sudden unless you started on steroids or other med.

Good luck


Thanks for the ideas, typ1! I wish those things could be it, but I can confirm they’re not.

Can’t be infusion site problems- I’m smart MDI.

Started a new cartridge right away, even though this was a brand new cartridge, new box, it was always in the fridge or a Frio pouch, and I didn’t receive a temperature warning from my InPen at any point.
And yes, there shouldn’t be a difference between novolog and humalog, and I don’t expect there to be, but it has been known to happen to people where they just don’t react to one brand. But again, don’t expect that to be the case since my 4am correction worked perfect. Which also means there shouldn’t be a problem with the InPen.

And finally, yes, I have been using the increased dosages of nearly 3x my normal rate (continues to increase each day) and still correcting if I don’t see change within a calculated time period- luckily the InPen can essentially tell you when you likely don’t have enough IOB to counteract your high BG.

So yeah, puzzling to say the least.

Oh, and to top it off, I have a cortisone injection scheduled for my hip tomorrow, which I likely have to cancel because my BGs will be dangerously high then and I don’t need an ER visit or hospital stay. FML :woman_facepalming:t3:


My insurance did that several years ago, and Humalog did not work well for me. I learned that I could use the $99Insulin discount card, and get 3 vials of Novolog for $99. (cash pay, not using insurance.)

1 Like

Thanks for the idea. If it is an issue with Humalog, I’ll have my endo write a letter of medical necessity. Hopefully not the case though!

You’ve presented a convincing set of arguments that it is Humalog. Now you might be wrong but it is much more likely that you are right.

The first step is to go back to your doc and say you are having an “adverse reaction” to Humalog. Sometimes words count. The massive increase in ISF and the lack of response to Humalog, which is sold as rapid acting, indicates, either, that Humalog is falsely sold or that you are having an adverse reaction. There may be other explanations but the first thing to do is to eliminate the obvious; only after that can a doctor state that whatever remains, however ridiculous, must be true.

There have been other reports of issues swapping from Humalog to Novalog. Common sense (well, maybe I should say my common sense) says that the two variants on insulin, which differ in two “bases” (one measure for how different hormones are), really do behave differently in different humans.

You presented your evidence here; you changed the insulin, nothing else. Your testimony is compelling. You do tight control (below 200) you are constantly aware of your BG.

The first, and only next, step is to switch back to Novolog. It is a no-brainer. Your doc needs to file it as an adverse reaction.

Years ago my insurance switched me to Novolog from Humalog. All I had to do was try it for a few days and while it worked it wasn’t quite as fast as Humalog on me. My doctor just submitted paperwork and I was okayed to get Humalog but at a higher price because it wasn’t on the formulary anymore, $180 for 3 months versus $100. After a few years Humalog was added back and it went back down.

They are different chemical make ups, so it very definitely can cause a different reaction. I tried Novolog again recently and it is still slower on me and just the addition of an ingredient for Fiasp, by the second dose, it literally was like injecting water.

So yea, one brand from another can definitely make a difference!

Not sure if anyone has mentioned this already, but it could be a different health issue. One time my high BG made me think I should test for Covid, which I had. I felt fine, but the only reason I tested was because of high BG.

Not saying it’s Covid for you, but almost any illness or infection or anything like that can cause spikes.


That’s exactly what I’ve been thinking recently. I know it’s not Covid, but I am wondering if I have an infection or something else… that’s the only type of stuff I could see causing this besides the change in insulin-which is so far proving to not be the case since I switched back to novolog yesterday and while it’s made a slight difference, it is only slight.

Thanks for the suggestion!

1 Like

Our insulin use gives us insight that others do not have. Let us know if you get anything confirmed @svlasak!

I have used a syringe to extract insulin from a pen many times, and it’s actually rather difficult. I have to frequently exercise all my bubble-removal techniques.

I do it the other way around; I load the pen and put the needle into the pen end; then depress the pen plunger. I also then know exactly how many units I put into the syringe and then into the pump.

Understood, but I think my use case is different. Most of the time when I’m using a syringe to extract insulin from a pen, it’s because the pen is “empty” I’m scavenging the last 8-15 units past where the plunger will push.

That said, when I’ve used done as you describe to fill a syringe from a pen, I might dial in 20 units on the pen but do not get all 20 units on the syringe (maybe just 18 or 19) unless I “help” by pulling backwards on the syringe plunger to get it to match at 20. But pulling back on the plunger too much would likely introduce new bubbles. I know at least part of this mismatch is the dead space in the needle and at the head of the syringe plunger (but that totals to less than a unit maybe?)

Haha I do that too and in order to get that last 0.1 cc I start with a few ccs of air in the syringe and inject into the pen cartridge. Even though I’m fortunate enough that I don’t have to pay for my insulin I hate wasting even a little bit.