How fast before your insulin kicks in?

I have been a type 1 diabetic for 23 years and strangely enough I still don't have any idea how long it takes for my fast acting insulin to kick in. I tested today at lunch and I was at a high of 21.2 mmol/L. I believe that I had breakfast without taking my insulin. After something being like second nature it's funny how you can forget if you actually took it or not. Anyways, I went for a 7.5km run and it took me 41 min. I thought that my blood sugar would be relatively lower but to my surprise it has only gone down to 19.0 mmol/L. This is what made me wonder how long does it take for insulin to kick in? Should I take more? I take Novorapid; 1 unit for each 10g of carbs ingested as well as Lantus before I go to bed. I've looked it up online but of course like everything else the answers vary from one side of the spectrum to the other.
I'm hoping that maybe one of you well educated diabetics or diabetes worker can help me out.



It's supposed to start working in 10 or 15 minutes, but I remember my endo telling me if you work out when too high, you end up higher. It's something to do with stress placed on the body during exercise. For me, once I'm that high from missing a bolus, it takes a lot longer to come down regardless of exercise. It usually results in over correcting and hypos later unfortunately. Hope it's different for you.


Here is a chart with some of the various insulins on that compares the kick in time, peaks and duration. I use Apidra and it takes 20 minutes to kick in for me. Just because someone else has a 20 minute wait doesn't mean that will be the case for you.

Thanks Charlene. You are the second person to tell me about the highs related to exercise. I've never been told that by any of my doctors despite having been in competitive sports for the last 15 years! Urgh! I really need to get myself a new diabetes doctor.
Thanks again for your input.

I think that MegaMinxX hinted at this. The insulin may have started working by just stopping your BG from going higher. And then it took longer to actually start bringing down your BG. Actually your question is a good question and not easily measured as the other posters mentioned many of the factors that can affect the insulin lowering your BG.

I find it takes much less insulin to stop me from going higher than it does to bring me down once I’m high. So if I forgot my breakfast bolus, it might take me two or three times the amount of insulin to bring it down than if I’d just taken the proper meal bolus.

No one said it was easy to figure out Type 1…

As with everything in D, YDMV, your diabetes may vary. How insulin acts in me most likely will not be the same with you, but for me I just switched from humalog to apidra. While my CDE said they are equivalent in action and activity, I have found that humalog acts like a bull dozer, in 15 minutes it is already lowering my blood sugar, and if I am not high enough to begin with, or I do not eat enough carbs to cover the bolus, I will invariably end up with a hypo and it continues to act for close to 5 hours. In contrast, apidra acts more like a slow train, it takes longer to start working probably close to 1/2 hour, and does not cause the huge swings in my blood sugar. It also clears out of my system a lot faster, so within 2.5 hours it is gone. So if I totally mess up the carb calculation I can always correct a bit sooner with apidra. You said you have your I:C ratio at 1:10 but is that the same for every meal ? And also do you have an ISF or correction factor for the times your blood sugar is that high ?

Ok, I'm confused. You talk about running, but you don't mention correcting. Did you take insulin to correct your high?

With a blood sugar that high (378) it's important to take correction insulin according to your ISF. I also have heard it is not appropriate to exercise when you are extremely high, though I couldn't explain the science.

Your insulin may kick in faster or slower at different times of day, too. So the idea is to test it out in yourself. Sometime when your blood sugar is up to 9.9, give yourself one unit of Novorapid, then test at 15 min., then at 20, then at 30. Find out. When it starts lowering your sugar will be the best time to eat. The problem is that if you do this in the morning, you may find that at supper it's different, so choose your tests!

Apidra starts working for me in about 15-20 minutes & lasts about 4.5 hours. Correcting highs takes longer because it seems that insulin resistance kicks in with high BG, or we're on an upward swing & not really correcting enough.

Adrenaline during strenuous exercise can cause highs, usually followed by lows later.


There's a risk of DKA when exercising with high BG due to dehydration & pushing BG even higher from the effects of adrenaline.

Thanks for the science, Gerri. Me, when I'm high I just take insulin! I still don't understand if the OP was attempting to correct that high without using insulin!

You know my philosophy about running:)

Novolog seems to start in 20 minutes or so for me but doesn't really get cooking for like 1.5-2 hours. I wouldn't worry about pushing your BG up exercising unless you are running really hard, like sprinting. I suspect it would have started to come down later. If I run high, I'll do a correction bolus and go run and don't worry about it too much.

When was the last time you were 378, AR?

Hi Stephanie,

my insulin kicks in real fast...I bolus right before I eat - UNLESS I am dealing with a high bg, then it takes longer to 'kick in'. I don't know why that is but when that happens, I wait till the correction occurs before I do anything else - including eating, exercise, etc.

I don't think you need a new diabetes doctor by the way. We are all so different, the best ones know that you have to learn what works for YOU. Sorry you had high bg like that, I bet my purse that it was a skip of insulin for your bfast and hope you are okay now.

Spring break maybe? I don't usually run up that hight but had a weird scene in LA, like the extreme end of a pump, 5 days or something and ran the pump out so I couldn't eat anything at the Entourage cafe...

I'd still run it down though. Exercise always seems to fast track correction boluses for me. I've read the "don't exercise when you're high" stuff but don't buy it. Get it down.

Hi Zoe,
I did take a correction before going for the run and that is why I was wondering how fast it takes to start acting. Sorry if my OP wasn't clear on that and thanks for your reply.

Thank you everyone for your knowledge and advice. I definitely need to sit down with my endo and figure some stuff out. For example I don't know what my ISF is and wasn't even aware that such a factor existed. I am not a perfect diabetic by any means and I really want to take control of this disease so thanks again for all your help.

Thank you MegaMinxX, your post was very helpful to me. I don't know what my ISF is but it is absolutely something that I will look into now. I've been having trouble with keeping my BG at an acceptable level and I really need to find what works best for me. Thanks again :)