Master Mind is 99% 4F-Methylaminorex (4F-MAR) is a stimulant that was first synthesized in 1960 by McNeil Laboratories. It is also known by its street names "U4Euh" ("Euphoria") and "Ice".

4F-Methylaminorex has effects comparable to methamphetaminebut with a longer duration.

The results of animal experiments conducted with this drug suggest that it has an abuse liability similar to cocaine and amphetamine. One study found that, "stimulus properties of racemic cis, racemic trans, and all four individual optical isomers of 4-methylaminorex were examined in rats trained to discriminate 1 mg/kg of S(+)amphetamine sulfate from saline. The S(+)amphetamine stimulus generalized to all of the agents investigated". A second study in which rats trained to discriminate either 0.75 mg/kg S(+)-amphetamine or 1.5 mg/kg  from saline generalized to aminorex as amphetamine stimulus but not to fenfluramine. Rats trained to discriminate 8 mg/kg cocaine from saline generalized 4F-methylaminorex to cocaine-stimulus. The reinforcing effects of cis-4-methylaminorex were determined in two models of intravenous drug self-administration in primates. Vehicle or 4F-methylaminorex doses were substituted for cocaine. One of the two different doses of 4-methylaminorex maintained self-administration behavior above vehicle control levels