MDMA users display a cognitive bias towards interpreting ambiguous information in an aggressive way a few days after taking the drug. Self-rated mid-week low mood and mid-week aggression do not persist 7 days after use of the drug. This pattern of results is consistent both with the acute and residual effects of MDMA on central 5-HT and with the notion that 5-HT plays a role in modulating human aggression.

The findings highlight the importance of controlling for other drug use (particularly cannabis) when investigating persistent effects of MDMA in humans.

The lowering of serotonin for a period following MDMA use could account for the increases in both self-rated and objective measures of aggression previously found in ecstasy users several days after taking the drug. There is some evidence of gender differences in the acute, sub-acute and long-term effects of MDMA use, and given that gender differences have been found in aggression, it is possible that men may experience more aggression mid-week than women. The aim of this study was to attempt to replicate findings showing increased bias towards aggressive material in ecstasy users several days after using the drug. In addition, to investigate possible gender differences in mid-week aggression. A total of 46 participants were tested: 19 ecstasy users and 27 controls were compared on the night of drug use and 4 days later. On day 4, a task designed to tap cognitive bias toward material with aggressive content was administered. Participants were required to process sentences that could be interpreted as either aggressive or neutral and subsequently remember them in a recognition test. This data set was then combined with the data from Curran et al.'s (2004) study that employed exactly the same procedure. Thus, the data from 107 participants was analysed to investigate gender differences. Ecstasy users recognized more aggressive sentences than controls and tended to react slower to neutral sentences than controls. Ecstasy users also rated themselves as being more aggressive and depressed than controls on day 4. No gender differences were found on any measure of aggression in the combined data set. Both male and female ecstasy users show a bias toward interpretation of ambiguous material in an aggressive manner when compared to controls 4 days after ecstasy use.

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Opiate users in maintenance treatment show a heightened ability to recognize facial expressions of disgust. We suggest that this may reflect increased exposure to other people's expressions of disgust and/or priming by the physical and social environments encountered by opiate-dependent individuals. Further, opiate maintained individuals' global slowness in processing emotional expressions may reflect the sedative effects of methadone.