The Outlook article 'Research without prejudice' (Nature 525, S12–S13; 2015) incorrectly stated that the approval of the US National Institute on Drug Abuse (NIDA) is required for US cannabis trials. In fact, NIDA provides cannabis for every project that has completed the government-mandated approval process. The article also implied that NIDA was holding up the start of a trial led by Sue Sisley, but the delay is caused by other circumstances.