MDMA is a chiral compound and has been almost exclusively administered as a racemate. However, an early uncontrolled report suggests that the (S)-enantiomer is significantly more potent in humans than the (R)-enantiomer[117][118] indicate that the disposition of MDMA is stereoselective, with the S-enantiomer having a shorter elimination half-life and greater excretion than the R-enantiomer. For example, Fallon et al.[117] reported that the area under the blood plasma concentration versus time curve (AUC) was two to four times higher for the (R)-enantiomer than the (S)-enantiomer after a 40 mg oral dose in human volunteers. Likewise, the plasma half-life of (R)-MDMA was significantly longer than that of the (S)-enantiomer (5.8 ± 2.2 hours vs 3.6 ± 0.9 hours). However, because MDMA has dose dependent kinetics, it is likely that these half-lives would be higher at more typical doses (100 mg is sometimes considered a typical dose). Given as the racemate, MDMA has a half-life of around 8 hours.