One of the most common mistakes I see are people getting "units" (i.e. marks on an insulin syringe) confused with IU's. For example, you may mix 5 mg's of HGH with 3 ml of water to make 1.666 mg/ml hgh solution. Let's say you want to take 2 IU's (0.66 mg's). You'd draw the insuling syringe back to 40 units to get 2 IU's of HGH.
Bottom line, IU's of a drug and "units" on an insulin syringe are two different things unless you are specifically taking about a standard insulin preperation.
P.S. mg's isn't a measurement of WEIGHT -- weight is a force. The mg's measurement describes mass ;-)