Reduced effectiveness of insulin

Hi y’all,
I am really enjoying this forum. Too bad I didn’t start reading this years ago :-). I’ve had T1DM for 40 plus years. I just started an insulin pump about 2 years ago… I waited until I had access to the hybrid closed loop systems before I started a pump because I preferred using insulin pens. But now it’s no going back for me because the closed loop system provides all sorts of great benefits.

One thing I’ve noticed in the past few months is that sometimes I have loaded my cartridge with insulin that appears to have reduced effectiveness. That caused me to have to change the amount of bolusing… which for a while made me frustrated and a bit confused of why I was getting different kinds of readings. Most likely some bottles of insulin reduced effectiveness because I love international travel and exploration… and some of the bottles probably were exposed to too much normal temperature (versus cooler refrigerator temperatures), longer than they should have been. With the pump and CGM became very aware of this situation and finally figured out the cause of why I would be suddenly getting different kinds of readings and different insulin needs than before. Have any of you had situations where you determined it was actually the insulin effectiveness that was declining, versus your management and body causing readings that were different than usual?

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I’ve had insulin degrade after exposure to heat/sitting too long in a cartridge (like more than 6-7 days). I usually adjust my basal rates and only realize it was insulin degradation not my body needing more insulin when I switch to a new vial and have to drop my basals back to where they were.

Hi Erin @PDX2022, we are happy that you enjoy this T1D Community Forum and with your years of diabetes wisdom - and with your experience traveling with diabetes - I suspect that your suggestions and tips have added value. I joined the original TypeOneNation forum while still working in the early 2000s after living with diabetes for 45 years and then rejoined 10 years ago when the Forum affiliated with JDRF.

Based on my experience I can suspect that a few reasons might be affecting or causing your apparent need to change bolus ratios - and possibly basal rates.

Insulin deterioration: Travel and exposure as you suggest; heat or possibly freezing if packed in luggage in an airplane belly. Florida heat doesn’t appear to affect my insulin and I never refrigerate a vial once opened.
Your Body: I’ve lived with diabetes about a quarter century longer than you have and now find that my insulin needs can change more often than I’d like. What I have found, is that as I age [octogenarian] is that my insulin requirement has gone quite low, 19 upd, even though I eat 230 - 250 grams of carb daily. I do adjust my pump with the smallest decrements/increments.
Length of Time Insulin in Cartridge: Insulin in cartridge beyond 7 days should be discarded - printed info sheet packaged with insulin. Something about insulin interaction with plastic and crystallization, I believe. This kind of puts the kybosh to pretravel preparation.

The CGM is the best tool yet for effective diabetes management, yet it has limitations and when used with an iAIDs, is to not always take the number automatically loaded into the pump calculator. Rather, follow the instruction in the April 2017 FDA letter that approved the Dexcom G6 for insulin dosing - the first device ever with dosing approval; use the number posted, with arrow(s) after viewing three previous reading dots. Keep in mind that the calculated dose is only an estimate/recommendation. I sometimes change the dose volume knowing what my activities have been or will be and consider MY experience with foods I’m eating.

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Thanks for your reply. The day I switched to a cartridge using different vial of new/fresh insulin, I started having way too much hypoglycemia [i.e., low blood sugar problems all day long, which is never fun.] So I think it’s important for all of us to keep in mind yet another possible factor in the multi-variable T1DM management framework – the idea of checking for degraded insulin/ less effective insulin. I certainly was not so aware of it until I started using the pump with CGM.

Hi Dennis,
Thanks for your tips and wisdom! I have read numerous of your postings. One thing that you said is something that I definitely look further into: “Insulin in cartridge beyond 7 days should be discarded - printed info sheet packaged with insulin. Something about insulin interaction with plastic and crystallization…” I was using a tip that I picked up from someone else to fill several cartridges to have on hand for quick changeover, especially when traveling [i.e., when you don’t want to pull out a needle in public to fill up the cartridge :slight_smile: :-)]. Lise just mentioned that she had a cartridge go bad. Anybody else want to add a comment about this?

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Hi @PDX2022 welcome to the party. I use an older pump system so my insulin never stays in a cartridge more than 2-4 days. I see greater variability from ongoing reaction between my body and the infusion set. Over time, for me , it seems the absorption at my infusion set site can vary. I prefer being a little close to muscle (not too close because it’ll hurt). If I’m just close enough to muscle I see great absorption, based on my CGM, if I’m in a bad spot, I see less and this can account for +/- 15% of my total daily insulin use. I travel internationally as well just got back to NJ from Singapore. I don’t typically see heat degradation as an issue. Cheers safe travels! :shamrock:

Clarification (my fault for not being clear earlier)- the cartridge itself didn’t go bad, it was still functioning perfectly when I replaced it. The issue was that I prefilled it and then inserted it into my pump several days later. I use my cartridges until they’re empty so the insulin was in the cartridge for like a week and a half total and started to degrade. Thats what you get trying to cheat the system for sake of saving money, time, and awkwardness of filling cartridges in public. Don’t know if that changes the meaning of your question or not :slight_smile:

Hi Lise,
Thanks for the additional information/clarification. Maybe I wasn’t clear in my reply :slight_smile: :-). I’ve read several of your posts and you do an impressive job in your communication! Based on your articulate postings, I was curious whether you plan to pursue a career in the healthcare field :-). Thanks again!

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Oh wow!! I hope to go to Singapore for conference in September. Maybe you can give me some tips for that country. I don’t know the rules for this discussion board about contacting people outside of it. What do you think-- can we talk?

And thanks for your tips about infusion sites affecting blood sugar variability. Yet another variable to think about! :slight_smile:

hi @PDX2022 Erin, sure we can talk, ill reach out on DM

Hello All,

I have a related question. I am traveling to Europe this summer. Last time I went was right after I was diagnosed, about five years ago (the diagnosis actually prompted me to start living life more!). I used a Frio pack, which works by evaporation. I use pens, no GCM, and no pump. I just prefer that. Anyway, the Frio pack cannot be closed up in a purse or bag (because of the evaporation thing), which makes it a little tricky. Not only do I have to keep checking and adjusting the contents of my purse, but I have to leave it open, which doesn’t seem super smart when traveling. Has any used any other system that might be better?


When my family travels in Europe I close my bag but put the frio pack at the top/in the front pocket so that it’s only the fabric of the bag covering it and it works just fine. If you’re using a water tight or super heavy fabric (leather, insulation, etc) the frio pack won’t work.
If you’re in Europe, you can look for a decathalon- they’re like a REI but with lower quality and lower prices. They have lots of bags that are meant for hiking/walking around the city and are decent quality, I’ve used my stuff for multiple years. Their mini basic backpacks are like €5-10, the perfect size for my supplies/extra snacks/water bottle and are the perfect weight for keeping the frio packs inside on the top of everything else. You can find those stores in almost every large/capital city in western and southern European countries, if that helps.

Thanks Erin! You’re right- I’d love to be a nurse, maybe even a diabetes educator if everything works out. I was totally uninterested in the human body before I was diagnosed- now I find it fascinating.

Thanks for your reply - I will keep that in mind!


It’s good to hear that you are interested in the possibility of working as a healthcare professional. I’ve read numerous of your postings and I’ve been very impressed at your knowledge and your compassion. You do look young :-), so you probably have many choices ahead of you as far as which way to go. If you start becoming more interested in the workings of the mind, there are professions such as being a health psychologist or rehabilitation psychologist that straddle both physical and mental health. I think having T1DM can help people become good scientists if they choose that direction as a profession, because they’re constantly thinking about multiple factors [variables] and cause and effect. Thanks for all your input! Best wishes, Erin

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Hi Dennis,
I was wondering whether you or your doctors have figured out why you need less insulin as you age. Just curious. Thanks for the comments/ideas. Erin

I just learned a new term called “insulin fibrillation,” which may be one reason why Tslim gives a limit on the number of days insulin should be in their cartridges. Here’s an article in case you want to read about that term.

Erin, there doesn’t appear to be a “logical” reason for reduced insulin needs. A doctor said that it could be related to more physical activity now that I’m retired, although when I retired July 4, 2010 when I reached age 70 my insulin needs increased even though I began bike riding 20 - 30 miles three days weekly and tutoring math at a local college. My insulin needs began decreasing in my late 70s & 80s after I stopped the biking because of some loss of balance; now I just walk 5+ miles 6 days each week.

It is not Tandem that places the 7-dal limit. It is Food & Drug and the manufacturers of analog insulin. The warning is printed on the info-sheet packaged with insulin - at the very end after about a million words.

Insulin does not have to be refrigerated after starting use and is effective for 30 days at regular temps up to 85 degress. In fact injecting cold insulin reduces it’s effectiveness. I will submit that what you think is “bad” insulin is just your normal body and every human body. I can eat the exact same thing and start at the exact same glucose level and use the exact same amount of insulin and one day that works and one day is does not. It is not the insulin, it is your body being itself. Ask any endocrinologist. there are at least 20 things that affect your digestion and for me, emotion is THE thing that will negatively affect my insulin effectiveness. If I have to be around certain people I do not like, I can eat a regular meal and take the correct amount of insulin and my glucose will be over 300. It is not the insulin, it is just being a human.

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Hi Erin,

Glad you found us! Yes, I have had insulin go bad/turn/degrade. It doesn’t happen often, but it does occur.

As for traveling with insulin, I use a cooler with ice packs when possible. I also use Frio pouches when I am not sure if refrigeration will be available. These pouches cool by evaporation, so all that is needed is some cool water, which can be found most places! I recommended them to my mother, also T1D, when she took a trip to Europe. They work great!

I’ve also gotten creative in the past, before I had my Frio pouch. As most hotels have ice available, I would fill the ice bucket and put my ice pack (blue ice/gel pack) in the bucket overnight to at least partially refreeze it. Or, I would bring zip locked bags with me and fill them with ice!

One thing I found is that insulin should not be placed directly against the ice/ice pack, as it can get too cold as well as too warm (when left out). So, I always put a barrier between the ice and my insulin. I have a medical bag now that offers a separate pocket for the ice, but in the past, I used a baby bottle bag that was designed to hold two bottles with a divider. I would put my blue ice in one side and my insulin on the other! Now, of course, blue ice has been replaced by gels for travel.

Hope this helps!

Pam K.
T1D 58.11 years and counting!

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