Diabetes, Meds

Fiasp Insulin: Why It's Different & How It Works

fiasp insulin - fiasp insulin review - what is fiasp insulin - rapid acting insulin - fast acting insulin

Meet Fiasp: the latest addition to mealtime (fast-acting) insulins. 

While Fiasp insulin is still in the “aspart” category like Novolog, Apidra, and Humalog, it’s a different insulin -- and it may not be ideal for everyone.

Manufactured by Novo Nordisk, Fiasp starts working in your body within four minutes. While we often think faster is better, One Drop's certified diabetes educators caution that for certain meals and for certain people with diabetes, it may be too fast.

Why is Fiasp faster?

It’s actually surprisingly simple: they added niacinamide (vitamin B3) to Novolog insulin. The vitamin B3 “helps to increase the speed of the initial insulin absorption," explains Novo Nordisk.

This means it makes its appearance in your bloodstream within approximately 2.5 minutes.

It also contains a “naturally occurring amino acid -- L-Arginine -- for increased stability,” which means it should work more steadily in your system after it peaks.

Comparing Fiasp to today's fast-acting insulin options

Take a look at all five of the fast-acting insulin options currently available to get a  better understanding of this unique timing feature. (Check-out OneDrop’s Guide to Insulin, too!)





Fiasp (aspart)

2-15 minutes

30-60 minutes

4 hours

Novolog (aspart)

15 minutes

45 minutes

3 to 5 hours

Humalog (lispro)

15 minutes

60 minutes

3 to 5 hours

Apidra (glulisine)

15 minutes

60 minutes

2 to 4 hours

Afrezza (inhaled)

4-15 minutes

35-45 minutes

1.5 to 3 hours

Fiasp was designed to more closely mimic the natural physiology of human insulin produced by a person without diabetes to prevent those pesky post-meal blood sugar spikes. By getting into your system faster, it helps to absorb the glucose from your digested meal more quickly.

While most fast-acting insulins would need to be dosed 20 minutes before eating to prevent that post-meal spike, Fiasp could be dosed up to 20 minutes after eating and still reduce that post-meal spike.

It's been described by expert CDEs as working “50 percent harder” during those first 30 to 60 minutes that it’s in your system, compared to Novolog, Humalog, and Apidra.

However, compared to Afrezza, it’s actually a bit slower. But Afrezza is an inhaled insulin -- not easily covered by insurance -- and thus, sort of in a category of its own.

Using Fiasp in insulin pumps vs. injections

Fiasp can absolutely be used in an insulin pump in place of Novolog, Apidra, or Humalog. But you should make this transition with careful guidance from your diabetes healthcare team, because it's not an equal exchange.

Remember, Fiasp is much faster, which means you may need less of it. And the timing of your doses will be different than Novolog, Apidra, or Humalog.

Most likely, you’ll find with your diabetes healthcare team that Fiasp requires a reduction in your basal insulin settings, and a reduction in your total daily insulin needs overall.

Fiasp may or may not be a better insulin for you

One Drop CDE and diabetes coach, Rachel Head, says Fiasp can be a great option for many, but it also may not necessarily be the best option for everyone or every type of meal.

“It works really fast,” explains Head. But for some types of meals, it’s too fast. "From a dietary perspective, if a person is eating a low-carb diet, Fiasp probably isn’t going to be a great choice for your mealtime insulin because the type of meals you’re eating will be digested more slowly.”

While the diabetes world often talks about wanting a faster insulin to prevent those post-meal spikes, you need to approach dosing your Fiasp insulin very carefully if you’ve been dosing Novolog, Humalog or Apidra for decades. 

If you think about the way you currently dose insulin for something like pizza, which is high-carb but digested very slowly due to the high-fat content, Fiasp could actually lead to some very rough bouts of hypoglycemia because it’s going to start working so soon.

On the other hand, it could lead to high blood sugars during the few hours after eating because Fiasp insulin is out of your bloodstream far sooner than other insulins. 

While anyone could take Fiasp as their primary meal-time insulin, just keep in mind that because it works faster, it could also result in more low blood sugars if you don’t consider what you’re eating and when you’re dosing your insulin.

According to Rachel Head, CDE, Fiasp could be especially beneficial for...

 People who eat low-fat, high-carb diets

For people who eat higher-carb but lower-fat meals, Fiasp could be a great option. Keep in mind that for high-carb carbohydrates the digestion could be delayed enough that you’d have to split your insulin dose to prevent crashing low before the rest of those carbs have been digested fully. A high-carb meal mixed with a lot of protein and fat would definitely require a split in your insulin dose.

For some children

Fiasp can also be helpful in dosing insulin in young children. Typically, you'd wait to give a young child their insulin dose for a meal because you can't be sure just how much lunch or dinner they'll actually eat.

By using Fiasp, you can dose insulin halfway through their meal, or even after a child is done eating and significantly lower that post-meal spike. *However, Fiasp had not been studied in children at the time this article was published, which means getting insurance coverage may be tricky.

During pregnancy

In the last few months of pregnancy with diabetes, women will find they usually need to dose their insulin 30 to 40 minutes before eating because of the impact of rising pregnancy hormones. Those hormones lead to tremendous insulin resistance!

Using Fiasp could reduce this lengthy, tedious and tricky pre-bolus time, ensuring that the mother-to-be could eat her meals with far less stress and lower post-meal blood sugar spikes. However, Fiasp may work a little too quickly for earlier stages of pregnancy during which hypoglycemia is more frequent -- during weeks 8 to week 20. (For women with gestational diabetes, check-out One Drop's Gestational Package!)

Common side-effects of Fiasp

Besides hypoglycemia -- which is a potential side-effect of any insulin -- common “adverse reactions” as reported by Novo Nordisk occurring in more than 5 percent of users included:

  • Nasopharyngitis
  • Upper respiratory tract infection
  • Nausea
  • Diarrhea
  • Back pain
  • Skin problems (like eczema), rash, itching

Remember, while this list might sound scary, there’s actually a similar looking list for nearly every type of insulin. For most of us, these side-effects are rare and nonexistent, but they are still important to know. 

The cost of Fiasp

Fiasp was first sold in 2017 at the same price of Novolog, but out-of-pocket costs for Fiasp could be higher compared to Novolog or Humalog.

Out-of-Pocket will cost about $570 for a box of 5 u100 pens. You can look-up your insurance coverage for Fiasp at NovoCare. See if you qualify for NovoCare’s Patient Assistance Program based on your household income. This program is designed for those living below the poverty level

It’s also still very new, so your insurance company may not have it on their list of “covered medications.” This means you’ll need a letter from your doctor stating your unique need for this insulin in order to get “prior authorization” from your insurance plan in order to get Fiasp.

Also beware that if your insurance company currently only covers Humalog (rather than Novolog, made by Novo Nordisk), this means they likely won’t cover Fiasp (also made by Novo Nordisk) easily either unless your doctor sends a letter to your insurance company explaining your unique need for this insulin.

What people are saying about Fiasp

Fiasp is still so new that very few people with type 1 or type 2 diabetes have tried it. We looked around the web and asked on Twitter to see what people had to say about their experience with Fiasp.

“I’ve used it extensively in pens, now in an Omnipod pump. I’ve found that its rapid onset of action has diminished slightly over time, but it’s still worth it over Novorapid for me. It’s rounded off my post meal spikes significantly and allows correction boluses to work quicker.” - @CountCarbula

“I switched to it in the summer from Humalog -- I love how fast it is, but you do have to watch out those lows a bit more.” - @WelfordP

“Yes, been using it for a while. Yes, I had to reduce the dosage a bit. Used Novolog previously. I don’t know what I’m going to eat always so this is perfect for me 2 minutes before eating or up to 20 minutes after eating.” - @DianeBerinato

“Used it for a while last summer but found after a while it became inconsistent -- a lot of unexplained highs. Went back to Humalog happily.” - @maireadyo

“My diabetes educator gave me a sample pen in July. I didn’t see a difference between it and my Humalog. Stayed with Humalog.” - @christifunky

“It was SUPER fast -- even a little too fast? I did reduce my insulin dosage a little. There was no burn for me. Felt like my usual Humalog. It was only a one-pen trial so it was a brief experiment, but I may have chosen to stay with my Humalog even if I'd had a choice!” - @KatherineRubida

“I found no difference with [Novolog], but it did sting during a bolus so went back to [Novolog].” - @james_thurlow

“Fiasp is hell. If you're okay with your current insulin, don't change. And if you do, do it when you have time to check and adjust a lot. I get high blood sugars I’ve never had before. I use about 30% more than Humalog and was still high. And I'm hungrier, and put on weight as a result.” - @Moumone1

“It worked beautifully for about 3 weeks: flat CGM profile and no post-meal spikes. Then it stopped working. I'm now on an almost double TDD. Waiting for my clinic to change back to Humalog.” - @markgdeakin

“I bought pens the last time I was in Canada. I use it for corrections only. It’s much faster than Apidra (which previously was fastest for me) and eons faster than Humalog and out of my system in about 3/4 the time. Since I only bought one box to try, I am only using it for corrections. I might when I get close to the 28 days so I don’t waste it.” - CSBD49

“I use Fiasp in my pump. There's a few ups and downs with it but on the whole, it's fine. Anything over 40 carbs then you need to split the bolus. I bolus just as I sit down to eat. The biggest mistake is people saying it's [Novolog] with added ingredients and then [using] it as they did [Novolog]. Its profile is different so treat it as a completely new insulin. As most people have found, injecting / bolusing the whole [dose] up front tends to cause a [low blood sugar] if there's a carb-load in that meal. Again, different foods need different splits. For me, an ordinary meal split would be 80/20 over two hours. To start with, I found Fiasp very frustrating and had been tempted on many occasions to just bin it, but now I'm used to it, and know what you can and cannot expect from it. I'm quite happy using it. It's absolutely vital that your basal is correct when using Fiasp, getting that spot on is the key factor.” - PumpkinUK

“I am on my 2nd sample Fiasp pen after making the switch from Humalog pens. I have found the insulin dosage to be the same between Fiasp and Humalog, but Fiasp kicks in a little quicker and tails off quicker. Humalog worked well for a long time until a couple of months ago when it wouldn’t kick in for hours and dropped me rapidly around 4 hours. My Express Scripts insurance formulary only covers Humalog, but my endo is going to try to get it approved.” - ChiGuy

“I only know, using for 10 days, that Fiasp, for me, has less ‘oomph’ than Novolog, and I think mixing (even in different shots) will be beneficial. The ratio now depends on initial glucose level and what I’m eating and inexperience. I also haven’t figured out how to do corrections well with Fiasp. Note: my first vial of Fiasp went cloudy and I stopped using it. I called, Novo Nordisk and they rapidly sent a return mailer and wanted it back, which I did. They also arranged for my pharmacy to provide a new vial at no charge.” - MonkMaster

“I have been using my Fiasp pen to bolus before dinner for about a week, and it seems to reduce the post-meal high somewhat, and sometimes causes my blood sugar to go low three hours after eating. Everything is still preliminary, so I will continue testing until my pen runs out.” - Don1942

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Ginger Vieira
Apr 15, 2019

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