I wouldn't use it until you call Eli Lilly unless it was only out less than an hour. I would say it depends on the room temperature also, if it was really hot, about 70 degrees or below the 38 degrees then I wouldn't use it. When I was using Forteo my doctor called the physician line and he was told that the pens could withstand 70 degree room temperatures for up to 14 hours per month max. He said this time included the amount of time it takes to give yourself the injections for the month. I never believed this and followed the instructions on the packaging. You can probably be issued a replacement pen free, Eli Lilly was pretty accommodating with me.