Rapid insulin effective time length

I wasn’t sure how to phrase this question in the title, so with a bit more detail here, hopefully it makes sense!

Dose the size of the insulin dose affect the length it is active?

For example, if I were to eat a large, carb heavy lunch and injected say 10 units of NovoRapid, would that last as long in my body as the 5 units I injected for my carb light lunch the previous day?

Common sense tells me that the larger something is, the longer it takes to disappear - think of a glass of water vs a bucket of water. If you were to steadily pour a glass of water it would be gone quicker than it would take to steadily pour the water out of the bucket.

But if they have the same active length, then the higher dose would be used much quicker during the first hour or so.

I’m tying myself in knots just trying to explain it! :rofl: Hopefully it makes sense though


Yes, generally the larger the dose the longer it will last - but it’s also affected by a million other variables like how fast it is absorbed at the injection site, what percentage of the insulin is destroyed/inactivated by your immune system upon injection, your exercise/activity level, stress level, etc, etc… Basically it’s always different!


you are making perfect sense, and this is a great topic. very curious to hear other’s experiences and answers as we all know YDMV.

Yes. There are two effects that I am aware of. One is that if you double the insulin dose, there will about double the amount that becomes active in your bloodstream after, say, 20 minutes. So the insulin will “start working sooner” in the sense that there will be more active insulin than digested glucose in your blood if you didn’t wolf down the entire meal within those 20 minutes. The second effect is that a very large dose of insulin in one spot sub-Q does seem to take longer to be fully absorbed, so it will seem that the insulin is actively working for a longer amount of time. Some folks call this a “long tail” of insulin activity because (with a generous imagination) the graph of insulin in the blood looks something like a mouse facing left, with a long tail on the right.


So, in my example of 5u on one day and 10u on another, would it make sense to split that 10u dose into say 2x 5u or 2x3u and 1x 4u, done at the same time, but in different locations? (Assume for a moment we’re not doing split doses for a high fat/protein meal)

Presumably the carbs would last longer too? I work on the assumption that my body can absorb or process around 30-40g of carbs per hour, so that 10u injection would cover about 150g of carbs for me and that would/should take 4-4.5 hours to digest/process. Would I be wiser to split that dose (maybe 50/50 or 60/40) to make sure I still had insulin definitely on board to process the longer carb duration?

Yes, to aid in absorption, this is what Dr. Bernstein says in his book,

Edited to add the section is " THE LAW OF INSULIN DOSE ABSORPTION"

As a rule, I recommend that a single insulin injection never exceed 7 units.

Following the above section is the section on " THE LAW OF INSULIN TIMING" which might be of interest to you.

I wouldn’t do that myself. I’d suggest to consider that strategy only if there is a specific problem you’re having and you want to see if splitting up the dose will help solve it. For instance, I’ve heard that Omnipod sites tend to leak or fail for some people when they use the pod to take a large bolus, so instead they use a syringe for that to help preserve the pod site. In earlier years on MDI I’ve taken as many as 33u in a single injection as the first part of a split bolus when I was a big fan of big pizzas, and the large dose all at once in one spot didn’t seem to cause any trouble.

I’m one of those people - in one sense.

My bolus range was 2 to 4 units and my highest basal rate is 0.9 u/hr and the back of my pod was always wet and bloody. I don’t think these are too large of a dose.

It’s me. My skin is very sensitive and I’ve come to learn, the surrounding tissue beneath the skin is too. I’ve come to believe that it can’t handle the the plastic canual as well as it should. I’ve been bolusing with a syringe for over a year now and use the pod only for basal.

We are all different and what works for one may not work for another. I love my pod, but as I’m moving toward Looping, I’m also strongly considering a different pump, with a canula that can go in deeper and at an angle suitable for my needs. I don’t know what that is, yet - but I do know I don’t have a choice with OmniPods, the canula is the canula and it can’t be changed.


You’ll need to experiment to find out what works for you. I have no trouble bolusing (with pen) up to 10 U or so. After that it sits there as a lump and I usually go high. But even then, to be on the safe side, I’ll split it in half and jab myself twice, if not three times. Because of Omnipod tunneling, I can’t bolus more than 4 or 5 U at a time with the pod, though extending a large bolus over a couple of hours doesn’t give me any absorption or leaking problems.


I like to even extend 5 units over 20 or 30 minutes. And this is with the Tandem X2 that already delivers the bolus fairly slow.

5 units 15% up front extended over 30 minutes would be typical for us.

Obviously there is a huge range from individual to individual as to what is considered a large bolus.


As far as injection sizes, I did split my Lantus dose into two injections during my third trimester of pregnancy #2. I was up to 40 units of Lantus a day based on prego hormones. I was seeing sizeable leakage so I split it into two 20 unit injections.

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