Abstract Background Problem use of illicit drugs (i.e. drug abuse or dependence) is associated with considerable health and social harms, highlighting the need for early intervention and engagement with health services. Family members, friends and colleagues play an important role in supporting and assisting individuals with problem drug use to seek professional help, however there are conflicting views about how and when such support should be offered. This paper reports on the development of mental health first aid guidelines for problem drug use in adults, to help inform community members on how to assist someone developing problem drug use or experiencing a drug-related crisis. Methods A systematic review of the scientific and lay literature was conducted to develop a 228-item survey containing potential first-aid strategies to help someone developing a drug problem or experiencing a drug-related crisis. Three panels of experts (29 consumers, 31 carers and 27 clinicians) were recruited from Australia, Canada, New Zealand, the United Kingdom, and the United States. Panel members independently rated the items over three rounds, with strategies reaching consensus on importance written into the guidelines. Results The overall response rate across three rounds was 80% (86% consumers, 81% carers, 74% clinicians). 140 first aid strategies were endorsed as essential or important by 80% or more of panel members. The endorsed strategies provide information and advice on what is problem drug use and its consequences, how to approach a person about their problem drug use, tips for effective communication, what to do if the person is unwilling to change their drug use, what to do if the person does (or does not) want professional help, what are drug-affected states and how to deal with them, how to deal with adverse reactions leading to a medical emergency, and what to do if the person is aggressive. Conclusions The guidelines provide a consensus-based resource for community members who want to help someone with a drug problem. It is hoped that the guidelines will lead to better support and understanding for those with problem drug use and facilitate engagement with professional help.