New member, but been on these boards roughly 6 years and have always been able to research and get the information on any questions without having to post. I have the Nutropin 10 pens and my question is after the pen is open how long is that individual pen good for. The information that came with the prescription says to discard after 28 days. My concern is I have already opened the pen and was not planning to start for a few weeks, so is the 28 days a precautionary or set in stone? Will I still be able to use it after that time and if so how much of the potency will be ruined?