I draw with 18g 1in and inject with 23g 1 1/2in. Some guys use 25g without a problem. It all depends on how much you are injecting. I inject a small amount of T so a 25g would be fine at my dose (according to my doc) if I had not bought a case of 100 23g needles and syringes. It does give me some flexibly if I choose to up my dose in the future.