I’m talking about prescribed vials which are meant to only be used for a month and not the diy vials which have enough for a whole year. I know that the preservative they use can’t really go beyond a month. And that if the preservative fails you might be injecting a pathogen directly into your body which is not optimal.
most preservatives in vials can last roughly 4-5 years in optimal conditions (away from sunlight and kept cool) though this will most likely be impacted by using the vial, youd run out of medication before the preservatives went rancid