Using Fiasp

I have never used Fiasp and my endo will not give me a script for it. She thinks it will give me some very bad hypos. I told friends in another D group about this, and a friend sent me a private message. Her son uses a Tandem pump, and the Fiasp is not working properly in the pump. Apparently Tandem recommends that Fiasp should not be used in their pumps. She has returned to Novolog, and now she has several unused vials of Fiasp. She wants to send them to me.
I am glad I will get the chance to try Fiasp, but I know I will need to change things a bit. I am tired of having post meal highs, sometimes higher than 180. I know the Fiasp acts faster, and may not last more than 3 hours. That sounds ok to me, but there may be some things I need to know that will keep me from having trouble initially.

Any suggestions or info frome Fiasp users will be much appreciated!!


We tried it, for my son it worked the same as Humalog. Same time to action, same profile. Stung a bit when injecting. For others they have shown it works faster. I suspect you won’t need to change much, but hope it works better for you.


Fiasp does not work the same for everybody.
Really the only way to know is to try it.

Tandem can not recommend Fiasp for their pump because the FDA label for the pump was only approved for Humalog and Novolog.

Fiasp actually works fine in the Tandem X2 pump. We have been using Fiasp in the X2 for about a year and a half now.

Tandem knows we use Fiasp in the X2. We are fully supported but Tandem can not suggest or recommend that we do this. Our Endo prescribed the Fiasp off-label for this purpose as she (the Endo) was very interested to see how it worked for us.


Like Chris’s son, I was underwhelmed by Fiasp. I hoped it would be a somewhat faster insulin that might speed up corrections for high blood sugar. But I couldn’t find any discernible difference between it and the Humalog I typically use. I tried it at least 30 times, and at least 10 times I recorded and graphed the BG results (this was before I had a CGM so I graphed it manually with Excel).

Fiasp insulin is the exact same insulin analogue as Novolog, with some vitamin B3 added which is supposed to speed up its action. If it IS faster, then it wasn’t different enough that I could tell the difference. But it is certainly worth trying to see if it works better for you. Based on what I saw I would try a one to one replacement and closely watch your BG just in case there is some difference for you. Hope it works for you!


@Thomas, thanks for this reply. I am going to forward a part of your message to the lady whose son is using it. I don’t know why it is not working well in her son’s Tandem pump. Maybe the pump is not an X2. Maybe she did not give it enough time and made a quick decision.
If she does send the Fiasp to me (5 vials), I will use it very carefully during a few weeks I have nothing scheduled, just staying at home.


When we first started using the Fiasp the difference in speed of onset was amazing. It was night and day compared to Novolog.

Obviously this has a big difference from one person to another in whether they see the speed benefit and also whether they get any of the unwanted effects such as stinging, burning or welts. We had the speed gain and no side effects.

Over the course of a number of months the speed of onset has decreased (I phrased poorly but I mean still fast but not as fast as it was initially) as compared to when we first started using the Fiasp but (for us) it still is substantially faster then the Novolog which we were using immediately prior to the Fiasp as well as the Humalog which we were using prior to the Novolog


Thanks @Thomas, you have been very helpful. The Fiasp is being sent to me in a plastic box with bubble wrap. I live in southern New York state, and the temps at night are freezing. I hope the insulin will not freeze. The sender lives in CT, so the distance is not that great.

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Same for me.

Could that possibly be a placebo effect? Maybe you got used to it and the difference was no longer amazing? Because if you are using different sites, trying enough different sites so that the location is not a factor (you have tried all the major body areas that you generally use), and you have a large enough sample size of attempts to examine, you would not expect it to slow down, right?

On the other hand, over a length of time a person’s GLUT4 expression can change, you may see a difference in the facilitated diffusion of glucose across the red blood cells membrane, a person’s insulin sensitivity can change, and so forth. And those things can affect the speed, but those changes generally happen slowly.

So this was over months, right? If that is the case, there could be other factors that made the Fiasp appear to slow down. There might be things affecting the speed besides the brand of insulin itself. Those might be good to investigate.

Somewhat related to the subject of insulin absorption and sensitivity, I highly recommend alpha lipoic acid supplements…


Hi Richard

My experience is almost identical to Thomas’. Yes, at first there was a bit more of a sting as compared to novolog, but I’ve gotten used to this and don’t notice it. I only do notice it when I have a large bolus.

Regarding how quickly it kicks in for me. When I first started using it (I think about a year and a half ago? Maybe a bit longer than that), it kicked in around 5-7 minutes (confirmed via finger checks). I have those experiments written down somewhere… Novolog at that time took about 30-40 minutes to kick in for me. I had been using Novolog for about 16 years. Now, agreeing with @Thomas, I feel like Fiasp takes a bit longer than that initial 5-7 minutes kick in time. For me, it’s more around 7-12 minutes now, confirmed with finger sticks. But like @Eric said there could be other factors at play in this regards.

I have used Fiasp in both a medtronic pump 670g and tandem x2 and have had no issues. I have heard that Fiasp is not as stable within pumping cartridge and tubing as compared to novolog/humalog, but that has not been my experience. The medtronic 670g cartridge holds 300u and I would replace the cartridge probably every 4-6 days for an idea of how long Fiasp was stable in my pumping supplies and my case.

I don’t think that Fiasp is a miracle insulin, but it helps me a lot with timing of boluses matching my meals since my schedule can be pretty hectic and prebolusing can thus be hard to time out.

I did not have to change much about diabetes management in regards to ratios and sensitivities, but the consideration I would suggest you make is the timing of pre-bolusing may change for you when you start using Fiasp. Like I said above, because Fiasp kicked in for me quicker than novolog, I can prebolus closer to a meal than I could with novolog. (Though I do still need to prebolus with Fiasp).


I started my X2 on Novolog, did ok.
When I switched over to Fiasp, I saw a big difference in reaction time and the tail.
The results were good, but diminish over time.
I switched back to Novolog for monetary reasons, and HATED IT!
I stayed on it for a couple months, and couldn’t wait to get back to Fiasp.
Fiasp is not a miracle cure.
But for ME, it works darn well!
Also, I noticed in the X2, I cannot use Fiasp more than 3 to 3.5 days without getting occlusions.
I also have to run a 9mm cannula on the 90 infusion sets.
Anything shallower than that, be it shorter cannula or angled, will cause me a lot of issues like occlusions or poor absorbtion.


I forgot about that part. We find that the Fiasp becomes totally ineffective (like it turns to water) if the site is left in 3-1/2 days or longer. We try very hard to never leave the site in longer than three days primarily due to the Endo telling us it is a very very bad long term problem to leave infusion sites in longer than three days.


Yeah. Good summary.


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Agreed! I change my sites every 2-3 days but my cartridges whenever I’m out of insulin, so not on the same schedule of the site if that makes sense

Edit: I change my cartridge whenever I get less than 30u left


Here is where those things get tricky, and you know this from your studies in medicine. There are always a lot of factors with BG. Maybe in a certain instance your BG would have dropped quicker anyway. Maybe it was on it’s way down, or you had not eaten as much in a previous meal, or all kinds of things.

If you had been on NovoLog, you would not have thought a thing about it. It would just be BG variability.

But when you started on Fiasp, maybe you are attributing those things to the insulin because it is new. And you think it works better.

As you know, those types of things are why they do placebos with studies.

That’s why this is a tough one to truly evaluate either way, other than by impartial long-term use and assessment.

Imagine how hard it is to do a true isoglycaemic clamp study, or a hyperglycemic clamp study, or hyperinsulinemic-euglycemic clamp study with subcutaneous insulin delivery!! Almost impossible, right?!

No. This is not a minor thing that needs a stop watch.

I understand this did not work for you so you may not be understanding the difference but it is not a minor thing.

If you read reports from various people the one thing that is consistent and significantly different as compared to Humalog and Novolog is that Fiasp really has a range of impact on people.


I considered that and it certainly can be done. But the extra scheduling seemed to push it over the edge of logistical scheduling complexity in terms of how it ended up being evaluated inside my head.


So we just do the site and cartridge together at the same time. With the rare exception of when a midnight cartridge hits zero and we really don’t want to do a site change so swap out the cartridge then get the site in the morning.


I am not knocking the insulin. Certainly it is worthwhile for anyone to try.

A big part of the problem is from the people marketing Fiasp and saying that now you can take your insulin up to 20 minutes after you eat. Misunderstandings can happen with that.

I can take any insulin 20 minutes after I eat, if I am dropping or did an increased basal prior to the meal. If I am low enough, I can eat without taking any insulin.

But marketing it like that can give people unrealistic expectations.

Truly, the only way to know for sure is for people to try it for themselves.

Gary Scheiner gives a review of it here:


Sure, but if we apply that mindset to literally any of the variables that we try to pin down, then we will always be reeling with doubt as to any true conclusions we’re drawing. ON AVERAGE, I see my bgs drop quicker when I hold all other variables the same (to the best of my abilities). Therefore, for me, I can comfortably say, the one factor changed, being Fiasp, could be playing a role in that quicker drop. With more and more data agreeing with this, I’m ok saying Fiasp for me does indeed drop me quicker than Novolog. Just for me, because there is variability in Fiasp’s timing. Sure that might not be the only thing that’s going on, just as all the rest of our variables act! It’s a guessing game, but I am comfortable with my data on this (whether you think it could be placebo or mechanistically different).

Ya, I don’t think that’s true for Fiasp and I try to be clear with that when I do provide my opinions on Fiasp.

I do think it can be an incredibly powerful tool for some patients but clearly doesn’t equal perfect control


I never knew this was a weird thing until recently when I switched over to tandem and had to get trained. My trainer could not wrap her mind around it :rofl: For me, the planning out of how much insulin goes into the cartridge based on my upcoming days is too much thinking :woman_shrugging:


Just to be clear - I am not doubting that it is faster for anyone really. Just the amount of the speed. Absolutely, there can be a difference.

But I think the “over-promise, under-deliver” thing happened with them.

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