4F-MPH [4-Fluoromethylphenidate]
4F-MPH is one of my friends. It's a very forgiving substance, even when snorting "slightly" too much, it doesn't rip you apart. It is able to make you addicted, especially if you try to be as productive as one can be, and maybe have got one or two ADHD tendencies.
Even tho it's very similar, more potency doesn't mean more concentration, 4F-MPH can be quite euphoric in higher doses, and thus dispels the effect it typically has on focus a bit.