Should a peptide vial be under vacuum when it arrives?

Often, but not always, and the absence of one doesn't mean the vial is bad. Freeze-dried products are stoppered at the end of the drying cycle. The FDA's Lyophilization of Parenterals guide notes the vacuum may be released and the headspace backfilled with an inert gas like nitrogen before the stopper seats. So a vial can arrive under partial vacuum or close to neutral. Both are normal. Headspace pressure also drifts up over weeks as the stopper releases trace moisture, per work in the Journal of Pharmaceutical Sciences, so an older vial reads closer to neutral. A held vacuum tells you the seal hasn't leaked. The real red flags are a puffed or bulging stopper, or a cracked or unseated cap. These are research-use-only materials, not approved for human consumption. We don't give reconstitution or dosing guidance; ask a licensed provider.