Can Insulin Go Bad? Here’s What Happened to One Patient
From: JR
I opened a new bottle of Humalog about four days back. My blood sugar has never been this high. Checked the Humulin and there were things sticking to the inside. Then I took a new one out of frigde. My blood sugar was 222. I took 10 units, checked my sugar 20 mins later. It was 320. I checked both new bottles and they have particles sticking to the inside.
Reply from John: Signs Your Insulin May Be Bad
Hi JR,
Thanks for reaching out. Based on what you described, it’s very likely that both your Humalog and NPH insulin bottles have gone bad.
How to Tell If Insulin Has Gone Bad
Any time you see visible particles or discoloration in an insulin vial or pen, it’s best to discard it and get a new one. The particles often come from coagulated insulin, which can stick to the sides of the bottle or float in the fluid. These are sometimes difficult to spot unless you’re in good lighting or know what to look for. Learn more about how to tell if your insulin has expired or gone bad.
What Could Have Caused the Insulin to Go Bad?
- Improper Storage Temperature: Your fridge or your pharmacy’s fridge may be set too cold. Insulin should be stored above 36°F (2°C). If it gets too cold—even briefly—it can break down and become ineffective. Refer to proper insulin storage guidelines from the American Diabetes Association.
- Contamination During Mixing: While less common, contamination from mixing NPH and Humalog could cause discoloration or changes in appearance. But this usually doesn’t result in particles forming.
A Personal Story: Even Pharmacists Miss It
Years ago, I went through 10 bottles of Humalog and kept having unexplained high blood sugar. With the right lighting, I could see tiny particles in each bottle, even though the pharmacist couldn’t. I eventually found that the fridge at the pharmacy was too cold. Once I switched to another pharmacy, the issue resolved immediately. You can view Humalog storage instructions from Eli Lilly here.
Bottom Line: Watch for These Red Flags
- Insulin looks cloudy or discolored (when it’s not supposed to be)
- Particles floating or stuck to the sides of the bottle
- Unexpected high blood sugar despite proper dosing
- Insulin feels cold or frozen after storage
If any of these occur, replace the insulin. Check your refrigerator temperature (aim for 36–46°F), and don’t let insulin freeze or overheat in cars or storage bags. The FDA also provides advice on insulin safety and use.
Please let us know how your issue was resolved!
– John