If a meeting becomes stressful, does it help, or make things worse, if team members drink lots of coffee? A study by Lindsay St. Claire and colleagues that set out to answer this question has uncovered an unexpected sex difference. For two men collaborating or negotiating under stressful circumstances, caffeine consumption was bad news, undermining their performance and confidence. By contrast, for pairs of women, drinking caffeine often had a beneficial effect on these same factors. The researchers can’t be sure, but they think the differential effect of caffeine on men and women may have to do with the fact that women tend to respond to stress in a collaborative, mutually protective style (known as ‘tend and befriend’) whereas men usually exhibit a fight or flight response.