I am reading it, and, except in one instance, it is refering to Disease and Toxins. "no ill effects" would seem to be referring to the effects of a toxin. It seems to be a case of poor wording, more then saying that "The Drug does not cause you to crash, or suffer addiction rolls." I know, personally, I would not allow someone to take it be able to get the good stuff but not the bad. I think this falls into a RAW vs RAI argument, and, generally, would err towards an interpretation that is logical.
I do not think the Drug Sam is going to be immune to the drugs coursing through his/her body. Also, you know...arguing about rules minutiae is not very punk of you people!

Edit:
Looking through the rules in the 2nd Printing of Arsenal, you have to go through a Toxin Resistance Test if you are taking the Natural Immunity, with Drugs assumed to be Power 6, and you have to manage to not reduce their power below your body for them to take effect.