Well first of all you have to keep in mind that Growth Hormone is misured in IU (international units), insulin is misured in U (units)...two different standards. Now, if you dissolve you're 18UI hgh powder (1 vial) with 1ml of sterile water you will get a solution of 18UI of HGH x 1ml. Then, if you're using insulin needles to inject that solution, you will use the U-100 needles, designed for those insulin brands that contains 100 U for each ml. Using your HGH solution of above with those insulin needles, you will have to aspirate up to the 12U mark to get approx. 2IU of HGH...it's just a matter of math. Hope you get it.