A question about efficiency of Humalog 25 days after opening a pen

I am type 2 but on MDI using Lantus SoloStar pens and Humalog Kwikpen JR pens. I put this in type 1 and LADA because you people are probably most experienced with insulin.

I never let my pens get hot. I live in south central Texas and we get hot here. I am beginning to notice a trend, where my BG doesn’t respond as fast or well when bolusing Humalog when the pen has been opened for 25+ days.

At first I thought it was because of higher insulin resistance, but I am pretty sure now that the Humalog is not as effective as it ages. I know some use insulin well beyond the 28 day window, so do you think I am right, and should slightly increase the bolus dose as I near 28 days? Thanks.

Welcome to another one of the unknown variables with diabetes. When I switched to a pump 17 years ago, Humalog users were routinely switched to Novolog because it was considered to be more stable in pumps. But tons of people use Humalog successfully. But I think I have kept that bias for no particularly good reason. I occasionally use Humalog instead of Novolog for no good reason except to change it up. I spend my winters in Arizona and did begin to think that Humalog didn’t last in my reservoirs as long as Novolog. (I use my reservoirs for 5-6 days.) But it was never a scientific analysis. I have to admit that Novolog probably degrades also because when I insert a new cartridge with fresh insulin my numbers are lower that first day. So it is probably worth a try for you to up your bolus amounts at the end of a pen. At the same time I use each Novolog vial until it is empty and that is about 6+ weeks. And I have used Lantus pens for two months. So who knows???!!!

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Lantus pens only last 10 days for me as I take 25 unit total in a day. I don’t use a lot of Humalog, generally 6u max 8u per day. So the pens are about half at 28 days.

My doctor originally prescribed Novolog (iirc) at first, but the insurance wouldn’t cover it. It’s always something, isn’t it?

For every person who thinks Novolog is better, you’ll find another person who thinks Humalog is better. Just go with what your insurance will cover.


If the pens are unexpired and at room temp it would be unusual for them to lose efficacy after just 28 days. But if that’s what you are experiencing, your bg doesn’t lie. It might also be kind of a sliding scale as the insulin ages.
You could extend the pen life with between-use refrigeration, or toss them after a month even if they’re not fully used, as sad as that is – depends maybe on your insurance benefit situation.

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It’s not a big deal, as I just do a slight increase of Humalog when I notice BG rising higher than usual after a meal. It still works but not as well.

I am fairly new to bolusing, only 9 months. I had to learn through by small increments how many units to carbs works.

My old NP that was a type 1 said she had a couple of patients that swore they noticed a difference by the third day of the insulin in their pod… I don’t know which insulin. I have also heard people think Fiasp is more sensitive to temps.

But I have heard of people leaving Humalog pens out for long lengths of time and it still working. In fact some people purposely used old insulin just to see if it still worked. In my case I kept forgetting to bring the frio pack for my back up Humalog pen left in the closed car when I snorkel for 3 hours and never noticed a difference. So now I don’t worry about it. The car gets decently warm although our outside temps never go above 85.

But my pens are probably never out of the refrigerator for more than 2-3 weeks? Most insulin is probably sturdier than you think. But you also have to keep in mind we can vary person to person in our response to things. MDMD


I have not experienced that at all. I use humalog from a vial, not a pen. My daily bolus/correction average is currently 12.0 units a day (I just checked Tidepool). My basal is Tresiba. My Humalog vials hold 1000 units. I always use a bottle until it is fully empty. I do not refrigerate after opening, keeping it always at room temperature. So after about 83 days I open a new bottle of Humalog and do not see any difference in insulin activity.

As a T1 diabetic for 47 years there are of course days where insulin sensitivity varies, some days requiring more or less for the same foods and activities. But if I continue to use the same vial I will see these short term variations in sensitivity return to where it was. I suspect that by changing to a new pen when you see one of these variations that you may be convincing yourself that your insulin has lost potency when it really hasn’t. But that is of course just my opinion based on my experience.


All the Lilly insulins say “Discard 28 days after first use.” Not clear why. They say they have a 3 ml vial for those who don’t need more than 3 ml = 300 units in 28 days, but those are not sold everywhere. I use my 10 ml vial until it’s empty, which is usually about 40 days, but I keep it in the fridge or in my Diabetica® icepack except when I take it out to give myself a shot, so not clear why it does not degenerate in an unopened vial in the fridge for up to 35 months, but an opened vial degenerates in just 28 days.
( I haven’t noticed any big difference after 40 days, and none of my endocrinologists warned me to always discard 28 days after 1st use.)

Great paper in PLOS Journal.
"Insulin’s shelf-life at 25°C=77°F (isothermal studies [15],) has been estimated at 199.1 days [16], and comparisons between isothermal and non-isothermal experiments have been published. "
So don’t keep your insulin at room temperature for more than 199 days.


I use Humalog junior only because there are times that 1/2 unit is appropriate. I was told not to use more than 28 days. Unfortunately, on some months, I find I have to throw what’s left away.

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