How long can T be open without being used?

[avjaro16]

I'm getting my prescription 4/25 and my friend is giving me a vial of T he never used because he switched from cypionate to enanthate. We use the same endo and pharmacy and I actually watched him purchase this vial so I know that it is not dangerous. The idea is I'll always have a spare vial of T, should I need it. The vial should last 3 months and expires 8/31 so I would have to use it up first. The problem is I won't see him until 5/10 and I'd rather not wait an extra 2 weeks to do my first shot. So my question is: If I use the vial I purchase for my first shot then wipe it clean, close it tight, and store it well, and then use the vial my friend gives me for the next 3 months, will it still be safe to use the first vial again after 3 months?

[Felix]

I don't know how effective it would be or if there would be degradation from air or whatever. Idk about contamination either. The vials I use don't open, but instead have a self-sealing rubber cap that the needle goes into.

Anyway regardless of what is officially the proper thing to do I wouldn't let that stuff go unused. It's not cheap and I can't imagine it doing much good in the sewer system or municipal waste stream if you were to dispose of it anyhow.