The ability to correctly identify affective information and to share emotions (empathy) is essential for human social interactions. Little is known about how psychostimulants such as the recreational drug 3,4‑methylenedioxymethamphetamine (MDMA, ecstasy) or the widely used medication methylphenidate (MPH, Ritalin) influence emotion recognition, empathy, and associated social behavior in humans. MDMA produces subjective feelings of openness and closeness to others and is therefore reported to have so-called “empathogenic” effects. However, it is unknown whether MDMA indeed improves affective perception (e.g. recognition of facial emotional expressions) and enhances empathy. MPH is used in the treatment of attention deficit/hyperactivity disorder (ADHD). MPH is a psychostimulant and acts as norepinephrine and dopamine uptake transporter inhibitor. Beside its use as a treatment for ADHD, MPH is also abused as a party drug and it is increasingly used as a performance enhancer, for example by college and university students. Little is known about the potential acute social cognitive effects of MPH. In the present project, we will therefore evaluate the effects of MDMA and MPH on social cognition and prosocial behavior using validated instruments and in collaboration with psychologists. The project includes 1. the analysis of already generated data from clinical studies conducted during my PhD thesis, and 2. the conduct of a new clinical study that I will initiate together with my successor Dr. med. Yasmin Schmid. This new study is funded by the SNF-SCORE grant of PD Dr. Matthias Liechti and has been approved by the local ethic committee and the Swissmedic, and has now been initiated. The study will include 30 subjects (15 male, 15 female) and use a placebo-controlled, crossover design with three experimental conditions: MDMA (75 mg), MPH (40 mg), and placebo. Cognitive empathy (recognizing emotions in others) and emotional empathy (sharing of experiences of emotions perceived in others) will be assessed using the Multifaceted Empathy Test (MET) and the Movie for Assessment of Social Cognition (MASC). Cognitive empathy will also be determined by the facial emotion recognition task (FERT). We will also assess the effects on prosocial behavior using a moral judgment task as well as a Social Value Orientation (SVO) test. All these psychological computer-based tests have previously been used in similar research settings by our collaborating psychologists and have been adjusted for the needs of the present study. Blood samples will be collected to determine the plasma levels of “social hormones” such as oxytocin, pre-pro-vasopressin, cortisol, and sex hormones. Preliminary data published by our group indicate that MDMA improves the recognition of facial emotions, but only for positive emotions (i.e. recognition of happy and not or angry faces). Our primary hypothesis is that MDMA will therefore have emotional-valence specific effects on emotion recognition but not enhance cognitive empathy overall in the present more comprehensive study. In addition, we hypothesize that MDMA will enhance emotional empathy and prosocial behavior. In contrast, we hypothesize that MPH will not produce such empathic effects but, as shown for amphetamine, MPH may increase accuracy of emotion recognition. Such an effect of MPH would be clinically relevant as it may contribute to the therapeutic effects of MPH in children with ADHD who exhibit impairments in emotion recognition. Because MDMA mainly enhances serotonergic neurotransmission and MPH mostly stimulates the dopamine system, the present study will also provide insight into the role of these neurotransmitters in social cognition and prosocial behavior. Thus, MDMA and MPH can also be seen as experimental pharmacological tools to study the processing of emotional information in this study. The proposed work is a collaboration of our psychopharmacology team with psychologists experienced this field: Prof. B. Quednow (Zurich), Dr. G. Domes (Freiburg i.B.), Dr. M. Crockett and Dr. C. Eisenegger (Cambridge, UK).