Several people mentioned in the spoiler thread and here the possibility that Luffy would end up, for whatever reason, taking the drugs. The whole "shave life off" thing is just too familar when it comes to him, isn't it? But in thinking about it, I don't think Oda will go on that direction, and I have a couple of reasons.
First, and perhaps foremost, is that, depending on how it's handled, it seems like it would undermine the whole purpose of the t/s power-up thing. The reason, we were told, that Luffy did all the things he did that were so dangerous, from involuntarily being stuffed with 100 shadows to Gear 2nd to taking healing hormones, was to allow him to fight on in defense of those who are precious to him–and we and he were in the process of being convinced of the absolute necessity of him powering up in some permanent way. Well, he (and we) were convinced, and said powering up has occurred. It seems as if it would be rather lame to have him resort to drugs to powerup on his first time of trotting out his new power, but maybe that's just me.
My other point is probably obvious, but bears stating because it comes up regardless, and has to do with the usual use of something like this in these sorts of stories--to have the hero face his dark side by means of some tempatation that is "a bad thing for a good end", with the hero coming out wiser but ultimately victorious over said temptation. OP isn't that sort of story and Luffy is so not that sort of emo character, so again, not happening.
One last possibility in favor of it happening, though, is a villain may somehow trick or force the drugs into Luffy for their own nefarious purpose--perhaps in this way bringing about the destruction of FI, somehow, at Luffy's hands. Oda would find a way to make such a dark scenario fit into OPs world, I'm sure. Things are definitely darker, now...
@Bulletproof--Of course! What better brand for pirates than "criminal?" LOL