Fiasp not working :(

Hi all,

I just started using Fiasp last week (on a pump) and have had crazy high readings ever since. I’ve tried changing set / site etc but nothing seems to work, I am definitely not finding the quicker absorption others have talked about.

Has anyone else had a reaction like this to Fiasp? Do I just need to increase basals and carb ratios or should i just give up and switch back to Novo?


Have you tried manual injection to remove the pump / infusion site from the equation?

Hi Tim,

No I haven’t, I just started on the pump in April so I’m a bit reluctant to go back to injections?

Not to go back to injections, but I am inclined to agree to try an injection to eliminate any trouble from the pump. We’ve been on Fiasp for a while now and love it. We find it quicker to absorb (unless it’s at a very insulin resistant time of day) and lasts 3 hours with a nice, slow decrease.

You don’t have to go back to injections, just try giving a couple of corrections with a syringe (or pen) to see if there’s any difference in the way they work compared to when infused with the pump.

Ah ok, thanks all - I’ll try an injection later today to see how it goes.

Are you waking up high? If so, that could mean that your pump basal rates may need adjusting. When pump basal rates are too low, you’ll end up high upon waking and even higher after eating. A solid customized basal rate is essential to keeping blood glucose in line.

Thanks Terry, I have had a couple of mornings waking up high or waking up in the night and needing to correct. I did a fast yesterday which showed my basal rates were working well during the day but as it was a Sunday I was probably more active than I usually would be on a working day. I need to do a fast to check them overnight and maybe need to increase overall.

My understanding is that Fiasp is not approved for pump use in the US (although it is in Europe). I don’t know that is because problems were found or there was just a lack of evidence that it was safe and effective.

It’s the same situation in Canada, but I think they are just being extra cautious. My endo, who is a type 1, told me he uses it in his pump and that the research has shown it is more effective when pumped than when injected. Having said that, I found it was not as good of a basal insulin when used in a pump due to what I assume is the shorter effective duration of action. I know it is supposed to have the same duration as NovoRapid/log, but it didn’t work that way in practice for me. I found I was much more susceptible to spikes from waking up, post-exercise, high fat/slow digesting meals, etc.

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I would agree with that. We found it lasts 3 hours, but kicks in faster than novorapid. After 2 hours, we can’t expect much action from it at all. I would agree that with things like pizza, pasta etc, a second bolus is required because it just doesn’t work long enough to take care of it.
However, I love the profile of it, how it kicks in fast, then drops slowly. We don’t see the double arrow down we often saw with novorapid. Also, can correct sooner if we know the dose isn’t going to do the job.


The internet has practically ground to a halt because of the extraordinary amount of traffic on Diabetes-related websites, Facebook groups etc., from people having problems using Fiasp in a pump. Reported problems vary but include:

Worked well for a couple of weeks, then ISF plummeted so TDD went up
Worked well for a while, then started getting major site inflammation/irritation problems
Worked well for a while and but needed a lot more basal
Worked well for a while but then had to use more insulin per gram carbs

There have been some suggestions that Novo really cut corners in their testing programme by using very few pumpers. Most test subjects were on MDI. Although the problems reported seem varied, they can all be explained by problems at the infusion site.

This might be one case where the extreme caution of the FDA is actually justified

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I am inclined to agree, I have now been on it for a week (4 set changes) and the first 5 days I ran very high but the last 3 seem to be much more stable… just a good sets? My last 2 sets have definitely been a bit sore though and have changed them after only 36/48hrs.

Not sure how much longer it’s worth persevering, i have definitely had some meals where i have seen faster absorption but not sure the unpredictability is worth it?!

I didn’t find it any faster and I also got welts at the pump site. It didn’t bother me when using pens, but I prefer to pump so I’m back to Apidra.

Thanks, Jenni, I’m the same, I’ve done a couple of injections just to see how it worked and was all good - but I’d also rather be on the pump so considering going back to Novo.

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Except for the site irritation, it seems to me these other problems have in common not finding the right adjustment with pumps. Needing more basal and needing more insulin per gram carb are possibly both responses to the same problem if the user and/or their physician don’t fully understand how Fiasp is working. In my own case, I was given Fiasp as a straight swap for Humalog, the only difference being that it would start working faster. Well, I discovered there’s way more to it than that, but my endo and CDE weren’t aware of that, and after a month of crazy numbers and tearing my hair out trying to figure out what really needed adjusting, I just gave up. (Plus I had site irritations, reason enough to stop.) The more I read of people’s experience with Fiasp, the more I’m left thinking maybe Fiasp isn’t the problem, it’s that the people prescribing it don’t yet understand how it works with pumps.

I am sure that this is true in some cases - people have not made the various adjustments to basal, ISF etc. However it doesn’t explain the first part of the statements in my list “worked well for a while…” For this fairly substantial group Fiasp worked pretty well for a couple or three weeks (maybe some adjustments needed but still pretty well). Then they started to see the problems I listed. Several of the reports (on Facebook) are from developers running hybrid loops (OpenAPS or Loop. These people are super expert and additionally have the looping data to back up their observations that their response to Fiasp changed after two or three weeks of use, and changed for the worse.

In my case, after a couple of great weeks (in which I DID have to change my pump basal and ISF settings), I started to develop serious red bumps about half inch across at the infusion site, eventually within a few hours of inserting the set. This is inflammation and clearly Fiasp IS the problem.

Do you know if any of the issues as you mention are being reported via the FDA’s Adverse Event Reporting System (FAERS) ?
“bad side effect” Is listed as an option in the Reporting System. IMHO, any side effects which you personally find significant enough to cause you discontinue using a product should be reported.

The original product descriptions reports, which I read when Fiasp was approved in Europe stated that a few users experienced temporary site irritation (I can’t remember the exact wording but that was the gist of it), but that this usually abated after a while. IIRC correctly from some of the comments posted elsewhere, most of the participants in the trials were using MDI, there were relatively few pumpers. If this is the case then they may well have missed some of these side effects.

I have tried to acclimate myself to Fiasp by using a mix of Fiasp and Humalog and was able to move from 1:4 to 1:1. However at 1:1 I still experienced frequent irritation at the site on day 2.

I understand that Fiasp is insulin aspart or Novolog with the addition of vitamin B3 and l-argenine. I experienced these pump bumps many years ago when using Novolog for a year or more. At their worst they were raised red welts about one and one half inches in diameter. I’ve read of other people who develop this infusion site inflammation. I don’t think it is unique to Fiasp.