Definitely store for at least 5 years if unopened and in a cool, dark place. My doctor gives me a 10ml/200mg/cc test cypionate every month, even though I'm only prescribed 150mg/week. According to my pharmacy, once you puncture the rubber stopper, it's only good for 4 weeks. Then you're supposed to toss out the rest of the oil and start a fresh vial. That's just so the pharmacy can sell more, but I'm sure most have used opened vials for many, many weeks. I have used 30ml bottles for months, never a problem. But will a properly stored vial lose potency after 5 years? Personally, I don't think so. And if it does, I think it would be only a few milligrams at most.