THE F SHOULD STAND FOR FUNCTIONAL 4F-MPH (4-Fluoromethylphenidate) emerged during the course of 2015 and fits very much into the functional category: a stimulant with little or no recreational edge.
In the wake of a ban on five named phenidates (ethylphenidate, 3,4-dichloromethylphenidate, methylnaphthidate, isopropylphenidate and propylphenidate) we were coming to the end of the research chemical road in this country, with this being one of the last throws of the dice.
I found it to be strong and noticeable even on low doses, with a bit of a jittery edge (albeit less than its sister compound 4F-EPH).
It certainly isn’t one to make a habit of, and with such a low dose threshold it demands particular care and caution.
I used it a handful of times for specific purposes; but that was it.
Refs: The Drug Users Bible [Amazon: https://www.amazon.com/dp/099559368X]