[MonikaT]

If the bottle is unopened, most supplements are good for at least two years from date of manufacture. If the bottle has an expiration date, then go by that to assess potency. In most cases, all that happens over time is a loss of potency, but there are things that can become potentially toxic such as aspirin and ibuprofen. I don't know if PM can become toxic, but if the color seems off or it smells different than it used to, I'd be inclined to toss it. Otherwise, at worst it might be a little weaker than it was when purchased, and that might actually be a good thing when starting over after a long break since it will make the ramp-up process a little easier.