# Effect of preservatives on insulin effectivity and site issues **URL:** \ **Category:** Tips, Tech & Gear\ **Tags:** insulin\ **Created:** [May 1, 2026, 11:12pm UTC](https://forum.fudiabetes.org/t/effect-of-preservatives-on-insulin-effectivity-and-site-issues/16019 "2026-05-01T23:12:23Z")\ **Posts on this page:** 1\ **Showing post:** 3
**Author:** ![jbowler](https://avatars.discourse-cdn.com/v4/letter/j/e274bd/32.png) [@jbowler](https://forum.fudiabetes.org/u/jbowler)\ **Post date:** [May 2, 2026, 1:25am UTC](https://forum.fudiabetes.org/t/effect-of-preservatives-on-insulin-effectivity-and-site-issues/16019/3 "2026-05-02T01:25:19Z")
I found @CarlosLuis 's early 2025 response particularly interesting: > [@Effectiveness of NovoLog vs Humalog in a pump](https://forum.fudiabetes.org/t/effectiveness-of-novolog-vs-humalog-in-a-pump/10978/22): > > Tandem says to change sites every 2 days with Humalog, 3 days with Novolog. It’s something to do with the reaction to the preservatives and the plastics. I find that Humalog is less effective day 3 as my suppies are on a 3 day schedule regardless of the insulin provided by the evil Pharmacy Benefits Managers of the day. See the remainder of the thread for the link to Tandem’s observation. Maybe it’s canula (plastic) dependent but clearly by that argument it would also be preservative dependent. Site reactions maybe the same, but what about the adhesive interaction? I don’t see Tandem blaming either the plastic (their canula) or the preservative in that link; neither word occurs in the PDF (the closest leading substrings are “representative” and “replacement”). Cannula gets 39 matches but mostly the ones of interest are about the cannula breaking or becoming completely detached, “dislodged”; the others are instructions. --- _[View the full topic](https://forum.fudiabetes.org/t/effect-of-preservatives-on-insulin-effectivity-and-site-issues/16019)._