Negative acute psychological effects experienced during or immediately after ecstasy use are reported in a sample of 98 ecstasy users residing in Northern Ireland (69% male, average age = 25, range 17-45, 50% living in Belfast area). Participants were recruited via direct contact, snowball sampling, advertisements in local publications and contacts with relevant organizations (such as student unions, health centers); recruiting was not done at clubs themselves. Qualitative data from the same sample has appeared in a previously published paper by the same authors (McElrath and McEvoy 2001). In the current publication, participants reported that their the acute effects of ecstasy they experienced were influenced by mood or expectation (set), beliefs about the "brand" of ecstasy used and observing the experiences of friends. Many ecstasy users initially did not use alcohol with ecstasy, but began combining the two drugs after they grew familiar with the effects of ecstasy. Some ecstasy users eschewed specific drug combinations because of the resulting negative effects (e.g. ecstasy and magic mushrooms producing panic attacks in one participant). The authors did not attempt to quantify any of the responses or to correlate them with actual reporting of negative effects. However, the information gathered suggests that the subjective effects of ecstasy can be influenced by set and setting and that ecstasy users combine ecstasy with ethanol and other drugs after growing familiar with its effects. The authors indicated that "most" participants reported having at least one negative acute effect, but that these effects did not discourage further use. Study findings confirm that drug contents, set and setting might play a role in mediating negative acute effects, but the paper does not provide any basis for determining which effect (if any) has the most impact or whether any one factor is related to a specific negative effect.