@Doug, I can assure that that advice the CDC give to only use a vial 1 time is stupid. ALL testosterone no matter what ester is made with Benzyl alcohol which is used as a bacteriostatic preservative. You will be fine.My prescription is 0.5 ml per week. So I am supposed to draw 1 injection and throw away the remainder of the 1.0 ml vial. I have noticed that the full prescription period assumes I use the entire vial so 5 vials are supposed to last 10 weeks instead of only 5. I believe their computer program just divides the total 5 ml (5 x 1 ml) by 0.5/week and comes up with 10 weeks.