The science behind this research appears to be as mixed up as the selection of drugs they are reporting on. If poly-drug users appear to be impaired in some way then you can only say, "one or more of these drugs involved may be responsible for this measured symptom and we don't know which", you can't say, "all drugs result in this measured symptom". The facial expressions research sounds like a recent experiment in which negative facial expressions are less likely to be interpreted as such whilst the subject is under the influence of MDMA. This effect was only noted while the subject was under the influence. I wonder if this news report is sourcing and getting its facts right. Or is this a soup made of several reports all mixed together?