FIASP not working

After 30+ years with T1D Humalog was taking up to 2 hours to work, so I switched to a combo of FIASP and Humalog. The FIASP worked great, started working within minutes. Then, after about a month, it stopped working totally. It was like injecting water. I am (unhappily) back on Humalog (injecting about an hour before meal, a real pain and not always manageable). I am hoping the FIASP will start working again after a while of being off it - if it does, I plan to use it only in situations where my BG has already gone high or I can’t plan a meal in advance. Hoping this way it will keep working for me (if it starts working again!). Has anyone else had this experience with FIASP? Any solutions?

Hi @BarryS Barry welcome to TypeOneNation. Solutions? Just maybe a really obvious one- how faithful have you been in rotating your injection sites? If I had to guess all the way from ‘Jersey… I’d say scar tissue. It’s possible you have some intermittent insulin resistance… or maybe not so intermittent if it’s all the time now, what does your endo have to say? Cheers good luck.

Hi Joe

Thanks. And yes, I always rotate the injection sites (good idea though!).

For the last 6 months I have also kept a record of where I inject (legs, stomach, etc.) each time so I could compare how quickly the insulin hits. Used to be that injecting in my stomach was generally faster than my legs, but that is no longer the case.

My endo hasn’t said anything except to recommend I go back on the Humalog, which I had already done. He also concluded general (intermittent) insulin resistance as a result of 30+ years of being T1D.

I am in the process of getting my first pump (a Tandem) which was going to use the FIASP, but now … Hopefully the Humalog will work out - I have yet to get the pump or training on it, but hopefully in a month or so it will all be done.

Thanks again for your response


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@BarryS A final thought, well, for now… Have someone you trust shoot you someplace brand new, like the back of your arm. Just poking around for ideas. Pardon the puns.

Hi Barry @BarryS, U know what you are saying when you think that Humalog isn’t kicking-in quickly enough after using it for a while; I began using Humalog the month it was approved bu US FDA - April 1996. I test-drove FIASP for a while and found it too erratic for my body, so beak to Humalog - I also used Novolog for about 10 years.

Even after using Humalog for so long I thought it didn’t kick-in quickly until I began using a CGM - watching the CGM I see it begins working within 10 minutes. Perhaps when you start on your Tandem pump and get your basal rates properly set, you will see the Humalog work better because of the necessary amount of basal working in you.

Hi Dennis
I‘ve been using the Freestyle Libre for about 6 months now, and it has been a great tool. It made me a bit OCD, moving from 5 or 6 finder pricks a day to checking it every 15 to 30 minutes (whenever i think about it).

It has made a huge difference in my BG. But it also confirmed how erratic my Humalog is, sometimes starting in 15-20 minutes, other times taking over 2 hours until the rise in BG even slows.

But i am getting a handle on it all, , A1C is better since i started with the freestyle. and then there will be the pump.

so all in all, despite the FIASP problem, things are working a bit better.

thanks for your response,


Yes Barry @BarryS the CGM was for me an eye-opener. I began using a Dexcom G5 218 months ago and just a couple of days ago upgraded to the G6 which operates Basal IQ on my pump. Prior to the CGM I had been doing 8 finger-sticks per day for many years. The CGM has helped me safely increase my HbA1c while decreasing my wide glucose swings and bring my Time-In-Range [TIR] to around <80% from 70%.

here is an excerpt from a paper recently published by The ADA about CGM use that included a reference to FIASP very similar to what I experienced and monitored with my CGM. Novolog is “usual insulin aspart”, FIASP is “faster acting insulin aspart” ; FIASP is Novolog with an additive.
… The double-masked, randomized, crossover study enrolled 20 young adult participants who previously used pump therapy. Participants received each insulin formulation from a closed-loop dosing algorithm based on CGM values for a 27-h inpatient stay. Time in range (70–180 mg/dL) did not differ between treatment with faster aspart (53%) versus standard aspart (58%). However, glycemic increments after meals were slightly greater with faster insulin aspart under these conditions. These observations illustrate how CGM can provide a way to effectively measure experimental glycemic outcomes and suggest that insulin delivery algorithms in closed-loop devices will need to be refined in order to realize any potential advantages of rapidly absorbed insulins …”; [Dovc et al.].

The entire paper can be found at :

That is what Afrezza is for! And I got Medicaid to approve it. Definitely takes work to get through insurance. Also has a few ways to get discounted without insurance. Warning. It is much more time sensitive and much less dose specific. Good luck.

Hi Dennis
I use a Freestyle Libre and i check it pretty frequently after an injection, though I know there is a time lag between actual BG and the Freestyle reading. Last night, e.g., after Humalog, waited an hour to eat, kept going up (to 15.2 mmol) for another 2.5 hours, and then dropped like a stone within 15 minutes, had to have sugar to prevent low BG. Other times, as you say, it starts to work within 10-15 minutes or so. Doesn’t seem to correlate with where I inject or anything else I can think of.

Hope the pump will make this easier. After 30+ years with T1D, i thought i would be better at doing this.



Hi Barry,
Sounds like you’re being very thorough in tracking your injection sites and blood glucose levels, but have you been tracking what you eat as well? Yesterday my blood sugar was high when I checked it for breakfast and then I ate more protein than I usually do for breakfast but I didn’t adjust for it, I just took the amount of insulin I usually would for the amount of carbs. Instead of dropping slowly throughout the morning like my BG normally would it rose for a few hours and then dropped a little, so by lunch it was about the same level as it had been at breakfast. I don’t think that happened because my insulin wasn’t working, I think it was because I didn’t take the right amount. So I’m wondering if something similar could be happening with you. I switched from Lantus to Tressiba about 9 months ago and increasing my Tressiba dose helped level out swings like that, but variations in my diet still have a huge effect on my day.

P.S. I also use a Freestyle Libre and I’m also trying to transition to a pump. I think having more flexibility and being able to make small adjustments will help.

I try to keep track of what I eat, though that doesn’t always work (particularly if eating out or at a friend’s, though having the Libre has helped a lot. The Humalog time to onset is still pretty variable, but I have found after being off FIASP for a a few weeks, it now seems to work again. But I am using it sparingly, only when I have high BG that Humalog has not handled for whatever reason (other health problems mess things up too) and that seems to work so far - but not certain about that yet. Still not sure how all this will work out with my pump (about a month away it now seems) but I hope it will make life a bit easier & that I’ll have better BG control.

Thanks Dennis
I’ll be switching from the Freestyle Libre to the Dexcom 6 when I get the Tandem pump.

Before the Freestyle my TIR was about 55% with 6-7 finger sticks/day . Now it is about 70% but I am still working on it. I am also trying to follow my Endo’s advice that “at my age” (>65) I should worry less about high’s and worry more about low’s (presumably I should have less time for long-term complications to set in, but more concern about heart attacks). I am having trouble switching to this attitude after >30 years, when all the emphasis used to be on lowering A1C, controlling complications, etc., particularly because I hope to be around for the long term, But I do get it, lows become more dangerous with age.

As for the FIASP, I am finding that after a few weeks off it entirely, it works if I use i sparingly - only when my BG goes high and Humalog will take too long.I find that if i take it more than once per day, the FIASP starts to lose effectiveness - it is not an issue of how fast it works, it just stops working.

For now it seems to be under control, next month a pump and everything changes


Thanks for your input. Yes, I am pretty careful with my carbs. I have been a T1D for over 30 years and am careful about all the basics. No signs of retinopathy, a little bit of neuropathy in my feet. However, my BG became much less stable after back surgery about 1.5 years ago. Hence the need for a pump, though I suspect I would have been better off with one years ago.

Good luck with your pump - I will get trained on mine this month and hope life will become simpler and BG control

will get better.