Yes. After 30 days, you can clearly see that there is still some liquid left in the pen for additional doses. If you use it on day 31 or 32, I wouldn't be concerned. I know there are some people who keep the pen refrigerated the whole time so that they can milk every last dose out of it, but apart from the preservative, it's not clear to me that the active medication itself doesn't start to degrade after 30 days. I just stuck to a 30-day schedule for simplicity.