Novolog vs Fiasp

In the beginning, I was completely sold on Fiasp; however, I am no longer sure that I will keep using it in my pump. Now that I’ve been using Fiasp in my pump for nearly two months, it’s about time I share my thoughts. Previously, I used Fiasp via pen injections for mealtime boluses, in addition to Novolog in my pump (used as basal).

To break everything down:

Pros of Fiasp

  • Works within minutes after injection
  • No need to pre-bolus (if already in range) and can even bolus AFTER meal
  • Increased flexibility, due to above
  • Corrects high BGs extremely fast

Cons of Fiasp

  • Active insulin time only 2 hours
  • Need more insulin overall due to above
  • Burning, redness, and lumps under skin after use in pump
    • Note: I even experienced more burning, redness, and lumps with the Fiasp pen than I did with Novolog pens in the past.
  • Must change pump site every two days due to above vs 3 days with Novolog

Do the pros of Fiasp really outweigh the cons? 

I’m beginning to think the only disadvantage of using Novolog/Novorapid is that a pre-bolus is nearly always necessary. But I won’t need to change my site every two days and I will not experience burning, soreness, and lumps from pump sites.

And actually, one of the biggest surprises for me, is that I need nearly one third more insulin while using Fiasp than Novolog. Why? My carbohydrate and correction ratios have remained the same. However, the fact that Fiasp is only active in my body for two hours, I typically need to bolus another dose about one hour after meal in order to combat a late BG spike. This is not needed with Novolog as the active insulin time is 3 hours.

I will not give up Fiasp completely, but I may give it up in my pump. Using Fiasp via pens/injections is a great option for high carb, or unusual meals. And as someone who typically eats low carb, Fiasp is just not that advantageous compared to Novolog.

HOWEVER, these are MY experiences. What you experience with Fiasp may be completely different. Do not be afraid to try it and see how it works for you!

Leave your questions and comments below! I’d love to hear your input and/or experiences.


P.S. See other Fiasp posts here.



  1. Im having problems with what I think is teflon catheters after 20 years. I know about scar tissue so I changed sites and still seem to go bad and thinking sometimes sugar extreme highs because its not an even exchange. Thanks for posting going crazy figuring it out.Love to hear if anyone experiencing the same.


  2. I’ve been using Fiasp in my pump on and off now for about 9 weeks. My reactions are results are spot on with yours. I thought I was losing my mind! My basal needs have increased nearly 30% and I keep finding myself having to correct a few hours after some meals. So glad to know it’s not just me. Happy I tried it but not the best option for my body.


  3. Interestingly I find I use much less Fiasp compared to Novorapid and I’m still shocked at how much more potent it seems. I wouldn’t switch back, for me, Fiasp is much better.


    1. Yerachmiel, Can you clarify for me: You found NO change in the speed of the insulin but “reducing the time from infusion from45 minutes to 25 is an improvement”. How did you reduce the time drom 45 to 25 if the Fiasp doesn’t work quicker for you?
      T1 37 years
      about to start Fiasp, possible only for bolus.


  4. Boy would I love to discuss this with you. I have found NO change in the speed of the insulin but find it helps a little bit with the insulin allergy issue. Of course only having two weeks on doesn’t give me enough time to really know (using 50/50 as this was recommended way to use it). Not sure why it doesn’t work for me, but guess reducing the time from infusion from 45 minutes to 25 IS an improvement (and having insulin work at same strength day to day also a great blessing)

    I’m 56 years t1 (36 on pump) so length of each does lead to the allergy (and to running out of decent sites to infuse and use CGMS in)


    1. It’s quite fascinating that we all react to insulin so differently. Hopefully it will prove to be a nice new insulin for you!
      What do you experience as symptoms when you say insulin allergy?


      1. I have a 670G pump that self corrects BG so cannot sensibly use Fiasp pen. I used Fiasp in the pump for a few weeks but had the unpleasant skin reactions described by Leah. Fiasp is clearly not made for multiple doses at the same site. It helped to even out the BG so I would use Fiasp if not for the reaction.
        Thank you for the information site


      1. Just fast response – sometimes, not all times, big drops after eating, also big rises after eating – just too inconsistent so have gone back to Novarapid/log outside EU and plan on a bit of manual mix and matching


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