Rapid insulin taking many hours to act

I am a newly diagnosed type 1 as of September '18. I am 52 and this diabetes management has been anything but. I originally responded well to rapid insulin, but the last couple of weeks my Novolog (and now Humalog) will not work at all to cover my meals, only to drop me 6 or 7 hours later like a rocket. So, I tried many times experimenting with fasting in the morning and my bs will be anywhere from 90-130 in the am and will be fine until I eat a meal at noon. I bolus correctly for my carbs (which are very low), and wait 15 minutes and an hour later I’m climbing. By the time the 2 hour post meal mark hits, I have gained sometimes 100 points or more for just 20 carbs that I had bolused for at a ratio of 1-10. The scary part for me is when it catches up after a dinner and I crash at 2 or 3 am. My bolus doses are usually very low because of my low carb diet- usually only two to four units before a meal.

At low bolus doses for low carbs, do I need more insulin just for it to work? Why did my ratio seem to work before, when I was eating more rapid carbs, and now it doesn’t that I’m on a low carb diet? My injection technique is the same, and I rotate sites. I’ve tried waiting as much as a half hour before eating. I had been using Novolog, but changed insurance and am having the same result with the Humalog they cover.

Can I ask how recently you were diagnosed and is it possible that you are in what is know as a honeymoon period. During this time a persons beta cells may still be working some, possibly sporadically, this honeymoon can last for a while in some LADA diabetics and be short lived in others.

Insulin production does not always shut off like a faucet. You could be seeing a further slowing of your insulin production. In LADA it will eventually reach zero or near zero.

In one aspect diabetes is like the weather, the only thing constant is change. We must continually adapt.

Some suggestion you can try. A fifteen minute pre-bolus might not be long enough, try experimenting with longer times.

2 to 3 am crashes are not that unusal, a lot of people will have a snack at bed time, something with some protein that will stay with you. Also timing of basal injections can make a difference

Bolus rates are not necessarily the same all day long.

I’m sure others will have more and better suggestions than I.


Did this start with going low carb or were you already having problems? Do you have a CGM? It would be easier for you to spot patterns with one and the alarms will take away most of that middle of the night worry.

What I would do is take the amount of insulin that I think is correct for the meal and then wait for it to start dropping me then eat what I dosed for. Watch your BG very carefully if you do this since that sudden drop when the insulin kicks in is dangerous if you aren’t paying attention.

Are you dosing for the protein in your meals? Many people need to calculate for protein as well as carbs. It can be anywhere from half to the entire bolus dose gram for gram.

If all else fails you may want to consider trying Afrezza. It is such a short duration insulin that you will be unlikely to go low using it and it also kicks in within a few minutes.

Welcome to TuDiabetes! You have found a place with a wealth of information about diabetes. I hope you find it as useful as I have over the years.

Let me start by saying that diabetes is a moving target. As much as we depend on math formulas to help us dose insulin, things change from day to day and even meal to meal. Expecting predictability is not reasonable. You may use a certain dose size for a certain meal and get good results for weeks but then you don’t. You need to roll with this new reality and adjust. The sooner you adjust, the better you will feel.

Recognizing and responding appropriately to this inherent variability will lead to conducting your own personal diabetes experiments. This is a fundamental skill that will reward you mightily if you use it to learn about your unique metabolism.

This to me looks like symptoms of a basal insulin out of whack than it is a fast-acting insulin meal dosing issue. Rapid acting insulin has a limited duration, usually less than 5 or 6 hours. Dropping rapidly 6 or 7 hours later indicates to me that your basal insulin needs to be adjusted. Problems with meal insulin will occur during the time from when you dose and up to 5 or 6 hours later.

The first step in setting up any insulin program is to get your basal insulin coverage dialed in. You need to do this before you can successfully adjust your meal-time doses. You don’t mention taking a long-acting basal insulin. Do you also take Lantus or Levemir, or Tresiba once or twice per day? Here’s a good reference to Gary Scheiner, type 1 diabetic, author, and diabetes educator, that teaches how to adjust your basal insulin.

If your meal insulin leaves you high 3-5 hours after your meal then you insulin to carb ratio (I:C) needs to be made more aggressive - you need more insulin. If you currently use an I:C of say 1:10 and it leads to going higher 3-5 hours post-meal, then you could experiment with 1:9 or even 1:8. Write things down as you experiment so that later analysis is easier.

Many of us who use a low carb way of eating often learn that we need to dose for fat and protein as well as carbs. If the body does not have enough carbs to convert to glucose, it will look to protein and fat to provide energy. I count 50% of my protein grams and 10% of my fat gram as “carb equivalents.” I add these carb equivalents to the actual carb grams that I eat and then calculate my meal insulin dose based on actual carbs + carb equivalents.

This might appear overly complicated now, but I can assure you that using it for a while will help to make it second nature.

Out of all the variables you must contend with to treat your diabetes, the one that is the most under your control is your diabetes knowledge. Invest in that knowledge base and it will reward you ten-fold. I recommend reading Gary Scheiner’s Think Like a Pancreas and John Walsh’s Using Insulin to start.

This will get easier! Be tenacious and when you start to get better results, you will feel empowered. Stay in touch; we are here to help you. Good luck!


I’ve been relatively low carb since I was diagnosed this past September. I’m fairly lean and haven’t been showing any signs of insulin resistance but I’m wondering; maybe there are 2 separate things going on. All of this craziness started a little over a week ago. Last night I lost 100 points in 3 hours between 2:30 and 4! I had been running high with Toujeo and now also with Levemir so I tried a bolus test this am. I took 2 units of Humalog and didn’t eat or have coffee…I started at 214 and after 1.5 hours I only went down to 202. So…I’m definitely insulin resistant all of a sudden. I’m guessing I have an infection. Why I crash at night (100 too 150 points) is the bigger mystery. I’m taking a split dose of Levemir 7u in the am 7u pm.

@CMiska Your high AM blood glucose could just as likely be a result of dawn phenomenon (or dawn effect). Your body, between 3-6am, releases cortisol, adrenaline, HGH and glucagon. All of which temporarily cause your insulin resistance to spike.

In other words, if that’s what happening, you need to increase your insulin:carb ratio for the waking hours.

If you have a CGM this blood sugar spike is easy to see.

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Thank you Terry4…I will get Using Insulin. I have the other one. I’ve been stalking this forum for months just to learn. When I finally decided to sign up I was hoping you’d be one of the ones to respond! You seem like a wealth of information and I also appreciate the moral support. I will work on my basal right away. Thank you so much


Many of us experience relative insulin resistance in the morning. Our bodies experience a circadian flow of other hormones, like cortisol, and that contributes to relative insulin resistance. It’s one of the reasons that I delay my first meal to mid-day, often after 11:00 a.m.

Here’s my continuous glucose monitor (CGM) trace from yesterday morning. This glucose bump is caused exclusively by morning insulin resistance. The yellow upper limit line = 120 mg/dL (6.7) and the red lower limit line = 65 mg/dL (3.6). I would actually go higher than this but my automated insulin dosing system dynamically increases my basal pump insulin to counteract this rise.


If I weren’t hooked up to my automated system, I would likely take a small amount of fast acting insulin when my feet hit the floor in the morning. You could also consider splitting your Levemir doses to add more to your evening dose to counteract this phenomenon. For example, instead of an am/pm spilt of 7/7, you could adjust that to 6/8. The extra Levemir unit taken at night could help the morning control. You would need to do the experiment to test this.

Be aware that this process can take some time. It could take a week or two to get satisfactory results. Aborted basal tests due to out of range glucose is common. Do not get discouraged. Persist and you will be rewarded!

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Wow what a difference! I can’t believe how good my numbers are today. I had heard about bolusing for protein and fat but I thought that was only if I wasn’t eating carbs at that meal. I would bolus for fat and protein but only eaten without carbs. So, all day I’ve combined the two and I’m amazed at how well that works for me (today lol). And I noticed that even though I spiked after lunch it came back down within 3 hours. So tonight I waited 30 minutes before bolusing dinner and rubbed my injection to speed it up. I’ll see how it goes. Please cross fingers that at least I don’t drop 100 points while sleeping…I don’t have enough to spare with these good numbers! Thank you all again…you’re lifesavers. I feel like myself today :smiley:


Be careful with this conclusion. If you were 214 and rising, the insulin first stops the rising before heading down.


Have you considered Apidra or Fiasp? Both are much faster in and out of the system. I’ve been on Apidra for many years after experiencing what you’re talking about when I was on Humalog.

That’s weird because, typically, it should be out of your system by then. Humalog and/or Novolog have an onset of action of 5-15 minutes with a peak effect 1-2 hours afterwards. The duration of action is 4-6 hours.

Something isn’t right.

FWIW, I routinely get the greatest BG drop 3+ hours after bolusing. This doesn’t mean that the insulin isn’t still having its peak effect earlier, but that I have fewer COB at that point.

I think something isn’t right too. I tried my half-used Novolog pen and the tail is shorter for me, but I still have to bolus 1.5 hours before a meal. I’m suspecting at this point that I have a thyroid problem. I’ve read that that is the way the body slows down the metabolism of insulin. I’ve had a pretty significant drop in heart rate from the mid 80s per minute (my entire life) to the low 60s and even a few upper 50s. I also have been consistently bone chilled for weeks. I have a doc appt on Tues to get blood work done. I’m so newly diagnosed…I’m having enough challenges with balancing all of this. I can’t begin to imagine dealing with more health issues so soon. :disappointed_relieved:

FWIW, I routinely get the greatest BG drop 3+ hours after bolusing. This doesn’t mean that the insulin isn’t still having its peak effect earlier, but that I have fewer COB at that point.



I have a CGM and pump so I can see the onset, peak, and duration. A Humalog bolus effectively lasts 3 hours for me. My biggest drop in BG is between 2 and 3 hours.

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