Few studies have examined the impact of alcohol on metacognition for witnessed events. We used a 2x2 balanced placebo design, where mock-witnesses expected and drank alcohol, did not expect but drank alcohol, did not expect nor drank alcohol, or expected but did not drink alcohol. Participants watched a mock-crime in a bar-lab, followed by free recall and a cued-recall test with or without the option to reply ‘don’t know’ (DK). Intoxicated mock-witnesses’ free recall was less complete but not less accurate. During cued-recall, alcohol led to lower accuracy, and reverse placebo participants gave more erroneous and fewer correct responses. Permitting and clarifying DK responses was associated with fewer errors and more correct responses for sober individuals; and intoxicated witnesses were less likely to opt out of erroneous responding to unanswerable questions. Our findings highlight the practical and theoretical importance of examining pharmacological effects of alcohol and expectancies in real-life settings
