It will probably last far longer than the average person's ability to stave off the urge to use it.
Sarcastic remarks aside, i'm guessing it's pretty stable as long as it's completely dry and stored under the conditions you listed. It will last over a year i'm sure.
Hahaha assume the said user has somehow mastered the art of holding off. I think I might be there..
I’m wondering if it has the ability to survive 5-10yrs or more. I’ve had morphine sit on the shelf for years no problem. I’m sure someone has stumbled upon an old vial of heroin from back in the day and “tried it out” lol, just gotta find em.